Micro-Comm Users Service Guide
For Tower/Pump Station Loops
Using the onecard system
1. Introduction to Radio Telemetry
I. Telemetry frequencies and FCC Guidelines
II. Radio Interference
2. Components in the Micro-Comm System
I. RTU Hardware and descriptions
3. Operation of a tower/pump station loop
I. Loop system with added options
II. Levels of control within a loop system
4. Tools and skills required for service
I.
Hand
tools
II. Preventive maintenance and
calibration procedures
III. Recommended spare parts
IV. Preliminary observations of a working system
5. Troubleshooting and testing basics
I. Voltage measurements
II. Current measurements
III. Checking a fuse
6. Troubleshooting
Procedures
I. Symptoms of common problems
II. Problem solving
Appendix
Glossary of terms
used with a Micro-Comm telemetry system
Post warranty
information
Back to service portal main page
1. Introduction to Radio Telemetry
By definition, radio telemetry is the sending and receiving of digital signals by wireless. The earliest commercial use of telemetry was in the space program during the 1960’s. Important data had to be sent between the space capsule and mission control at a high rate of speed. Because of unreliable analog technology, digital telemetry was clearly the way to do this. By toggling digital tones off and on quickly, telemetry allows data to be moved faster on the same carrier frequency as the older analog systems. This in turn provided a simple, yet reliable method for wireless control and communication.
Today telemetry is found not only in the space program, but in commercial airline navigation, radio controlled toys, paging systems, garage door openers and many other applications. Wireless computer networks use a form of telemetry that utilizes several frequencies so data can be moved even faster.
Micro-Comm Inc. combines telemetry with the ability control pumps, monitor flow rates, generate alarms, position valves, change speed settings, and even gather data required for engineering water system expansions. The information in this manual should give you a better understanding of telemetry and your control system in general. With the growing number of telemetry systems in the United States, your knowledge of it will be invaluable!
Some terms used in this manual are specific to our product. To help with this, you will find unusual words and terms defined in the glossary.
I.
Telemetry Frequencies and FCC Guidelines
The radio signals used are generally VHF and UHF frequencies. In some cases the 900 mHz band or spread spectrum is used. The biggest problem in any radio system is a weak signal path. A path between any two points could be weak for any number of reasons including distance, large hills, foliage, power lines, etc. A good example of this is listening to AM radio when driving under a bridge and it fades out momentarily. Simply, the bridge causes a weak path for the AM receiver. Fortunately, FM frequencies don’t fade under a bridge, but come with a few problems of their own.
As a rule of thumb the lower the FM frequency, the less problems there are with signal path problems. Lower frequencies are generally allowed to have higher radio output (in watts). This higher output can help overcome a bad path problem. High frequencies are more directional, meaning that radio paths need to be line of sight with shorter distances and no obstructions. Because of their wider bandwidths higher frequencies seem to work better with increased data speed rates. As you can see, there are a lot of pros and cons regarding high and low frequencies. However, Micro-Comm has overcome these problems using techniques that will be covered later.
The increasing use of radio signals can make it difficult to license a system. In light of this, Micro-Comm uses narrow bandwidth or splinter frequencies. These are easier to license and are sometimes sandwiched between existing voice frequencies.
All Micro-Comm telemetry systems are licensed through the FCC and UTC. This keeps your system in accordance with all rules and guidelines that are in place for radio transmitters. Most importantly, the frequency used for your system has been specified by the FCC and the equipment is designed for optimum performance using this frequency. Remember the FCC license is granted to the user for the lifetime of the system and may be subject to renewal from time to time.
For more information of signal paths, refer to appendix G.
II. Radio Interference
Rarely there will be a problem with another radio system blocking signals within the telemetry system. Likewise, there are few complaints that the telemetry system is bleeding into the other radio system. In any case, if all of the FCC specifications are followed by both parties, there should not be any conflicts.
Radio transmitters have to be set to the correct output power (in watts) and be centered on the correct frequency and bandwidth that the license stipulates. Likewise, a receiver whose bandwidth is ‘too wide’ will pick up unwanted transmissions too.
Most of the time a radio will get out of tolerance because of age only. It would be a good idea to have the radios checked once per year or as soon as you have received a complaint. Remember, if the FCC gets involved, you want to make sure that your system is within the legal limits before they come to see you.
For more information about having your older radios ‘tuned up’, contact Micro-Comm for scheduling.
2. Components in the Micro-Comm system
I.
RTU Hardware
To make the Micro-Comm telemetry system more user friendly and easier to service, you will find that most of the components are completely interchangeable. This modular design not only simplifies the production of the system, but makes troubleshooting very simple. First, lets identify the components within a standard RTU and their function. (STD) refers to standard RTU equipment (OPT) refers to option. Refer to the Component layout of RTU I/O Subpanel figure for location of these items.
!Remember to always turn off all power and disconnect the battery before replacing components!
I/O Subpanel (STD) - This large circuit board serves as a wiring interface and mounting backplane for the components. All I/O subpanels are the same with the exception of added options and the setting of the address switches (see below).
(1) Onecard (STD) - This is the ‘brains’ of the RTU. Inside is a microprocessor and input/output processing components. There are different types of Onecards, including Marshall, Oneswap, Dataswap, Multicard, Update, Control, Control card II, and others. The same type of onecards are completely interchangeable with each other. Check the onecard labels before changing them. The onecard fuse (6) is an AGC ½ amp and is located directly below the address switch. To change the onecard, use a screwdriver to gently pry loose the two connectors. Then remove the two screws holding the onecard in place.
(2) Line filter (STD) - Also called Line Protection Unit. This device removes damaging electrical spikes from the incoming 120 volt AC power. In the event of a hard lightning strike on the incoming power, the line filter may be destroyed. However,most of the time only fuse is blown. Taking the brunt of the electrical surge, most of the time other components in the RTU are saved by the Line Filter. Power to the line filter is turned on by switch (33), which also turns on power to the RTU. Line filter fuse (32) is an AGC 7 amp. The orange neon lamp (34) indicates that power is on to the line filter. To remove line filter, use a phillips screwdriver to remove clear plastic cover. Then use a standard screwdriver to remove the two screws holding the line filter to the subpanel. Note locations of the colored wires before disconnection.
( 3) Power supply (STD) - Converts 120 volts AC to 13.8 volts DC. For the sake of discussion this is called a 12 volt power supply. The output is set for 13.8 volts for battery charging reasons. It supplies DC power for the radio, onecard, transducer, calibration circuit, entry alarm module, flow meter and any external devices requiring 12 volts DC. The power supply is mounted to the I/O subpanel by three screws. The fuse (4) is an AGC 2 amp type.
(5) Address Switches (STD) - These are used to set the two letter address (identity) for the RTU. No two RTU’s are addressed the same.
(7) Radio Test Jack (STD) - Means of plugging in a debug terminal used for testing and de-bugging purposes. The terminal can also used to view radio communications.
(8) Telemetry Control Lamp (STD) - When the RTU is sending and receiving signals on a regular basis, this lamp will be on.
(9) DC power ON lamp (STD) - This lamp is on to indicate that DC voltage is present on the board.
(10) Offset Resistor Terminals (STD) - If the calibration test voltage cannot be brought down below 5 volts DC, a 10k ohm resistor can installed between these two terminals to bring it down. In most cases the resistor is already installed. To put the resistor into the circuit, remove the wire jumper in place behind the resistor.
(11,12) Calibration Pots (STD) - Each pot goes with the test point below it. After connecting the DC voltmeter, turning the small screw on the calibration pot will adjust the calibration voltage up or down. Calibration procedure is covered in section 6 Problem Solving.
(13,14) Calibration Test Points (STD) - A DC voltmeter is connected here while adjusting the
analogs. The red (A) test point is commonly used to test the tower level
calibration. The blue test point (B) is a spare. The black (C ) point is
common. In pump stations sometimes (A)
and (B) are used for calibration of
discharge and suction pressure respectively.
Voltmeter use is covered in section 4 Tools and Skills Required for Service.
(15) Output relay sockets (STD) - When the RTU has control of pumps, valves or other devices, time delay relays are installed in these sockets. Dry contacts from these relays are wired to the corresponding terminals on the right hand side of the I/O subpanel. Call circuitry wired to these terminals will then allow the devices to be switched on and off by the relays. Relays are used to electrically isolate the RTU from the possible noise caused by the other devices.
(16)
Input indicator lamps (STD) -
When 120 volts AC is applied to the corresponding discreet input terminals on the right hand side of the
board, these lamps will light. They can be used to verify pump run, valve call
or any other type of discreet input. Note the 120 volts AC used must come from
the filtered power in the RTU. Inputs are typically wired through auxiliary
motor starter contacts, limit switches, etc. Output indicator lamps (STD) - When a corresponding output
relay is turned on, one of these lamps will light. This gives visual indication
the relay has closed. If relays are not installed, these lamps will not light.
(17) Battery dropout relay (OPT) - If battery backup is provided for the RTU, this unit must be installed. It provides the battery charging circuit and does the switching required when the AC power goes on and off.
(18) Entry alarm module (OPT) - Door and window switches can be connected in the circuit that uses this module. The entry alarm provides time delays required to enter and exit before the alarm goes off. Its output is normally wired to a discreet input to sound an alarm on the PDU or central. The armed/reset switch on the on the panel door is also wired to the entry alarm module.
(19) Spare socket (STD) - If another relay is required within the RTU, it may be placed here. Wiring for this socket goes to the terminals below it.
(20) Input terminals (STD) -Motor starter auxiliaries, valve position switches, floats, temp alarms, etc are connected here. Power for these is 120 volts AC. This 120 VAC power must be filtered power that comes from an ‘H’ terminal on this board.
(21) Output terminals (STD) - These terminals are connected to the T1-T6 timer relays on the I/O subpanel. They provide a ‘dry contact’ for each relay that is used to switch on motor starters, valve solenoids, etc.
(22) Spare socket terminals (STD) - These terminals provide connection to the spare socket.
(23) Battery fuse (OPT) - Required when battery backup is used. As protection for the battery, its type is an AGC 7 amp.
(24) Battery wire terminals (STD) - Leads from the battery are connected here. This terminal block also provides connections for keyswitch and door switches when the entry alarm is used.
(25) Input expansion connector (STD) - If more inputs are required, an input expansion module can be connected here. The inputs are 120 volts AC like the standard inputs mentioned above.
(26) Span resistor (OPT) - If transducers are connected to the RTU, span resistors are required to set the scaling. Span resistors are usually connected between A+ and A- or B+ and B-. Details on the use of span resistors is covered in appendix A.
(27) Input expansion terminals (STD) - If the input expansion module is used, connections for it are here.
(28) Door lamp terminals (STD) - These are connected to T1-T6 timer relays. When a relay is turned on, power will be supplied to these terminals to turn on a door mounted lamp.
(29) Radio connector socket (STD) - A ribbon cable soldered or plugged into this socket provides a power and communication link for the radio. The other end of the ribbon cable is connected to the radio.
(30) Thumbwheel and LCD jack (STD) - If an LCD display and/or thumbwheels are used, a connector with ribbon cable is plugged in here. Thumbwheels and LCD are usually mounted on the panel door.
(31) Radio Fuse (STD) - Fusing provided to protect the radio only. Type is an MDL 4 amp.
There is a smaller version of the I/O subpanel known as the I/O Card. It measures approximately 6” x 6”. It has the same components as the I/O subpanel except power supply, onecard, line filter, relays and large screw terminal strips are placed elsewhere within the RTU enclosure. By looking at an I/O subpanel, you can easily identify the components on an I/O Card.
Other items within the RTU enclosure:
Lightning arrestor (STD) - This device has an airgap where the center conductor of the coax is very close to the grounded outer shell. In the event of a lightning strike, most of the electrical discharge will arc from the center conductor to ground preventing damage to the radio and other components. It is very important that the lighting arrestor is amply attached to an 8 foot copper clad ground rod driven into the earth.
Radio (STD) - The radio used is an industrial type known for its ruggedness. Internally it has had modifications that include the cable and connector that come out the back. Note that this radio will not work for voice communications.
Patch cord (STD) - A cable used to connect the radio to the lighting arrestor. If the door of the RTU is opened frequently this cable may break down causing radio transmission problems.
The above described
components cover the inside of an
RTU. Outside components include the
following:
Antenna (STD) - Telemetry antennas are directional type with 8 decibels of gain or more. The larger VHF antennas have five elements, where the smaller UHF antennas have seven. The one element mounted in a white insulator is called the driven element as it is the only one electrically connected to the center conductor of the coax.
Ground rod (STD) - Eight feet long, the copper clad ground rod must be driven into the earth completely. It is attached securely to the lightning arrestor with a short length of #10 (or bigger) copper wire.
Transducer (OPT) - Standard with a water tower RTU and is used to measure the level of water in the tower. With between 10 ½ to 30 volts DC applied to it, a transducer will output electrical current based on the amount of pressure applied to it. With no pressure applied, it will output 4 milliamps of current. With the full rated amount of pressure for that transducer applied its output will be 20 milliamps. For example, a 100 psi transducer will output 20 milliamps with 100 psi applied to it. By measuring the pressure at the bottom of the tank, the RTU can determine the level of water in it.
For more information
about transducers, refer to appendix A.
For more information about span resistors, refer to appendix B
3. Operation of a tower/pump station loop
In its simplest form, telemetry can be used to send a water tower level to control a pump station that is miles away. The tower will broadcast its level to the pump station every few minutes. When the level gets to a low set point, the pumps will come on and continue to run until the tower gets to the stop set point. This configuration of tower and booster is called a loop.
The above described loop is very simple. However, a loop can have an array of options including alarm notification and remote monitoring. A Micro-Comm PDU (Portable Data Unit) is a hand held device that listens to the transmitted signals from the tower and booster. This unit will display current tower level, pump run status, active alarms and flow rates. The PDU listens to the system 24 hours a day at the office, in the truck, at home or anywhere in between.
An alternative to the PDU is a phone dialer. This unit placed at the pump station can automatically place a call the operators home or office in the event of an alarm such as pump failure, low and high pressures, station flood and high or low tower levels. A phone dialer is a limited alternative and does incur a monthly phone bill for the pump station.
I.
Loop control with added options
Now that we have an idea of how a simple loop works, lets add some things that are commonly used in a tower-pump station loop. In this system, a single pump station fills two towers. Also included are control valves, pressure backup, chlorine injection, an altitude valve, battery backup, PDU, flood alarm, HOA monitoring, phase loss and flow rate. We will address these things one at a time and discuss their function within the system. The system used for this example is one of several like it actually found in the field.
By adding an RTU in the same box at the pump station, we now have the capability to display both tower levels and use both levels for control if necessary. There are physically two loops in this system, but has the appearance of one loop.
Tower A is several miles from tower B. Tower A has an overflow that is lower than tower B. In this case, the tallest tower, B, is going to be the controlling tower because it will be the first to call on and last to shut off pumps. In essence, tower A just floats on the system using its altitude valve to keep from overflowing. Note that the measuring scale for tower B must be big enough to drop the water in tower A enough to open the altitude valve and turn over the water in it.
Tower “B”
Tower “A”
P
W
S
D
P
W #
S 1
D
#
1
Altitude Valve
Pump Station
Tower
/ pump station ‘loop’.
For example, both of the above tanks are standpipes each 100 feet tall but tower B is at a 10 foot higher elevation. By putting tower B on a 51 foot scale we could drop tower A nearly 40 feet ( a reading of 51 feet at B is full, minus 10 feet elevation difference with a pump start point of 1 foot). This should be more than enough room for the altitude valve at tower A to open and close. Most tanks are engineered to be at the same elevation, however Micro-Comm uses this method to overcome the elevation difference problem.
On a related note, the most common scaling factors used in your Micro-Comm telemetry system to measure tanks are 0-25.5 feet for elevated tanks and 0-51 feet for standpipes. These scales are set to read the top usable range of either type of tank. This scaling simplifies checking the status of water reserve in your system. For example, you have 6 elevated tanks. Knowing that a 25.5 foot reading is full and you see readings of 21.2, 20.5, 23.0, 22.8, 24.1, 22.8, you immediately know that all of the tanks are within 5 feet of being full. This makes checking larger systems very simple.
Now that we understand how the tanks will be filled, lets take a closer look at what is happening at the pump station. When tower B is low enough, a pump will be called on. At the same time the pump is started, power is applied to the pump control valve solenoid. As the valve begins to open, a timer relay tied to the circuit begins to time down. If the timer relay expires before the valve gives an open indication, the valve fail circuit will kick in. This circuit immediately shuts down the pump, avoiding a dead heading situation. Remember that dead heading a pump can lead to serious pump damage or explosion is the water is allowed to get too hot.
Likewise, if the valve had opened within its allowed time, the pump will continue to run until the tank is full. The pump is ‘locked in’ (running) as long as the control valve is open. A pump run condition will also start the chlorine injector. A phase monitor is wired into the pump call circuit. If line voltage drops significantly or one leg of three phase power is lost, the phase monitor will drop the pump call automatically.
Water flowing through the flow meter will register flow to the RTU. The flow meter gets DC power from the RTU and in return provides DC pulses. Raw pulse information is sent to the central or PDU where calculations are done and flow rate and total is displayed.
When the pump RTU gets the signal to turn off the pump, the control valve solenoid is de-energized and the valve will slowly begin to close. The pump will continue to run until the control valve limit switch gives a closed indication. At this point the pump will shut off completing the cycle.
Certain types of alarms are sent to the PDU or central and will not shut down the pumping operation but will require attention as soon as possible. These would include station entry, low tower level, flood alarm, low/high flow rates and chlorine leak . Remember that other types of alarms such as power failure, pump failure, valve failure, phase loss, and low/high line pressure will shut down the pumps and require immediate attention. Micro-Comm provides many alarms such as the rate change alarm that can notify you of a pending problem well before anyone runs out of water.
Non-alarming information is also available the to PDU. This can include monitoring the H-O-A switch position, control valve limit switch position, chlorine dispense rate, turbidity level, chemical feeder status, etc.
II. Levels of control within a loop
system
Radio telemetry works 24 hours a day, while you sleep, shop, go to work and do other things. It is so reliable that when there is a problem it may surprise you. Unfortunately, the biggest foe for telemetry is lightning. With antennas mounted
high and being connected to the power lines, an RTU can take a big lightning hit but still function to some degree. In this section we will cover what happens if the telemetry cannot function due to lightning or power failure.
During normal operation, a pump station receiving its respective tower transmission will turn on its Telemetry Control output (also known as System Normal). This output turns on a light indicating this status and will turn on a relay that is connected to a pressure backup system. The telemetry control output will go off if the pump station does not hear from its respective tower (or central) for a preset amount of time, usually 20 minutes.
The pressure backup system sits ready to go on line. When the telemetry control output goes off, the relay will ‘turn on’ the pressure backup unit. This unit will then call the pumps on and off based on line pressure until telemetry control comes back on. Most pressure backup units work marginal at best, as it is hard to control pumps based off of their own discharge pressure.
4. Tools and
skills required for service
As mentioned before, tools and knowledge required to service Micro-Comm equipment are minimal. With knowledge of basic math and tools you already have, you should be ready to go. In the next two sections we will describe exactly what you’ll need to perform basic service and troubleshooting procedures.
I. Hand tools
A small standard screwdriver (for calibration), large standard screwdriver (for opening RTU enclosure), small phillips (for removing line filter cover) a couple large adjustable wrenches (for transducer disassembly), and wire cutters. Sometimes it is handy to have a 7/16 nutdriver to open the outer RTU enclosure. A long standard screw starter works well when replacing hard to reach screws on the I/O subpanel.
A simple hand calculator and voltmeter are also needed. A less expensive voltmeter will work fine as you will need to be able to read DC millivolts and DC voltages up to 20 volts or so. Also AC voltages at 120 volts or less. All common
voltmeters cover these ranges. If your budget allows, a meter than can read milliamps (current) would be a big plus.
For more information on using a voltmeter, refer to appendix E.
II. Preventative maintenance and
calibration procedures
Generally a visual inspection of the system and calibration of the tower level are the only routine maintenance procedures we recommend. In some cases, there are older Micro-Comm systems up and running that have never had anything done to them. However, as you know, good preventative maintenance can help avoid costly problems down the road.
A good visual inspection of the system would include the following:
Antenna - Is it pointed in the correct direction; are all elements in place; any signs of wind or vandalism damage; are there any unusual bends or kinks in the coax; is the coax connector well covered with tape to keep out moisture?
Transducer - Disconnect it from its supply line and flush it out. A small amount of dirt or debris inside the transducer can keep it from reading pressure correctly. Remember to turn off the RTU when doing this because it will send a zero level reading while the transducer is unhooked from the supply line.
Coax connections - A corroded or loose connection between the radio and antenna can cause problems over time. It is a good idea to inspect the patch cord and antenna coax connectors going into the lightning arrestor to make sure they are clean. Using fine emery cloth, shine up the center pin of each of the connectors before putting them back into the arrestor. They should be snug but not over tightened. Make sure the patch cord connector going into the radio is also clean and tight.
Plug in connectors - Lightly push inward on the onecard ribbon cables where they plug into the I/O subpanel to make sure they are seated. Also make sure the connectors into the onecard are in all the way. Do the same for radio and power supply ribbon connectors.
Terminals - Check for frayed or loose wires on the I/O subpanel terminals. Use screwdriver to make sure they are tight.
Look for dirt and dust inside the RTU. Sometimes small insects find a way to get in where it is warm. If there is a greenish corrosion on screws, fuse holders or any exposed metal this could be a sign of a chlorine or other chemical leak. If this is found, contact Micro-Comm for instructions.
!Remember to turn off AC power to the RTU before touching wires or terminals when doing maintenance! AC power may be present on terminals located on the right hand side of the I/O subpanel. This power may be from another source. Turn off all associated breakers before servicing.
Standard tower calibration procedure
All towers within a Micro-Comm control system are put on a scale used to measure the useable portion of the tank. The most common scales are 0 to 25.5 feet for elevated tanks and 0 to 51 feet for standpipes. This means that either the top 25.5 or 51 feet (useable range) is measured. Pump control within the system uses start/stop setpoints that will call on and off pumps somewhere within this range. Using standard scales makes it very easy to check tank level, as opposed to using a full range scale and having to remember how tall each tank is.
Calibration is recommended once per year or after changing a transducer or onecard. Note-if you are changing a onecard, use the voltmeter to check the calibration voltage before you change the onecard. After installing the new onecard, reset the calibration voltage to the previous reading. This is done if the onecard is being replaced for any other reason besides a level problem.
Calibration test point connections.
Calibration is done to insure that the measured scale will show the tank to be full when it actually is full. If the calibration is off, there is danger of running the tank too low or overflowing it.
To calibrate, put pumps in HAND and wait for the tower to overflow. While it is overflowing, set your voltmeter to read DC volts and plug the meter leads into the calibration test points A and C as shown. Using a small screwdriver, turn the tiny screw directly above the A test point. Turn the screw in the direction required to set the voltage to as close to 5.00 volts DC as possible ( 4.95 to 4.99 is acceptable). Remove meter leads from test points. Procedure complete.
The calibration screw is purposely made small so that it is not accidentally bumped, thus changing the calibration setting.
For calibration of a
tower at that is not full, refer to appendix C.
Calibration of
discharge and suction pressure is covered in appendix D.
If calibration
voltage cannot be brought below 5 volts DC, refer to
appendix F.
III. Recommended spare parts for your
system
As mentioned before, lightning can cause a great deal of damage. Micro-Comm has minimized this problem by doing a single point grounding scheme which is covered elsewhere in this manual. Lightning is very unpredictable and sometimes even a small hit can cause problems. Fortunately, this usually affects only the items listed below. We recommend have one each of these items if your system has less than 10 RTU’s . If you have more than 10, we recommend you have two each.
Onecard - same in all remotes
Radio - same in all remotes
Power supply - same in all remotes
Transducer (one of each psi rating)
You will also need a good supply of fuses. We recommend that you have at least five of each type.
Onecard fuse - AGC ½ amp 250 volt
Radio fuse - MDL 4 amp 250 volt
Power supply fuse - AGC 2 amp 250 volt
Battery fuse - AGC 7 amp 250 volt
Line filter fuse - AGC 7 amp 250 volt (same as battery fuse)
Contact Micro-Comm for price and delivery of the recommended spare parts and fuses.
IV.
Preliminary observations of a working system
If you know what it should be doing, it is a lot easier to figure out what is wrong when its not doing it. First, lets learn what normal operation is all about. While the system is operating correctly, go to each RTU, observe it for a while and make note of these items:
Antenna direction.
What internal RTU
lights are ON.
What internal RTU
lights are OFF.
What internal RTU
lights go ON or OFF with a change (like pump call or run)
Listen to radio (or
tape it with handheld recorder).
Measure span resistor
voltage when tank is full.
Measure span resistor
voltage when tank is low (or empty).
When you are diagnosing a problem, the above information is invaluable. For example, by taping the radio tones you can refer back to the tape for comparison. By measuring the span resistor voltage, you can tell if a transducer is working correctly. This procedure is covered in an upcoming section.
Preliminary observation worksheet
Make copies of this page for each site
(observations made during normal operation-leave this page at site inside RTU)
Site name:_______________________________________
Antenna direction:_________________________________
Input lamps ON: 1___ 2___ 3___ 4___ 5___ 6___
Conditions that cause lamps to come ON:_______________
________________________________________________
________________________________________________
Output lamps ON:1___ 2___3___ 4___ 5___ 6___
Device that comes on when output lamps come ON:_______
________________________________________________
Span resistor voltage (tank full):___________millivolts DC
Span resistor voltage (tank at low end of scale):________millivolts DC
Other notes about this site: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
5. Troubleshooting and testing basics
Before actually diagnosing a problem, lets discuss the basics of measuring voltage/current and checking fuses. To check voltage on the power supply, span resistor and calibration test points, set the meter to read DC volts.
I.
Voltage Measurements
On the power supply there is a small circuit board with ¼” tall posts sticking up. These posts will have a red wire attached to one and a black wire to the other. They are also marked + and - respectively on the circuit board. Put the red meter lead on the post with the red wire (+) and the black meter lead on the post with the black wire attached (-). With power on to the RTU, the meter should read 13.8 volts DC. A reading between 13.5 or 13.9 is acceptable. There is an adjustment pot next to the posts. Using a small screwdriver, slowly turn this pot until the meter reads as close 13.8 volts as possible. If the power supply cannot be adjusted to somewhere between 13.5 and 13.9 volts, it must be replaced.
Even though this power supply puts out DC power, it would be wise to set the meter to read AC volts and check for AC voltage on the DC output posts as described above. If more than 1 volt of AC is measured, then the supply must be replaced. A few millivolts (less than one volt AC) should be acceptable.
A good place to check 120 volts AC going into the power supply is on the fuse located on the power supply. Set meter to read AC volts. Touch one meter lead to one end of the fuse. Touch the other lead to neutral or the lightning arrestor.
Note - a short in the DC circuitry can ‘pull down’ the power supply voltage a little but will not blow the fuse. A short could be caused by a bad onecard, transducer, I/O subpanel or any external 12 DC device connected to the subpanel. After the short has been found and repaired, re-check the power supply to make its output is correct. If it is not, then the shorted part may have damaged the power supply.
Checking voltage on
other parts of the subpanel
Reading the voltage across the span resistor is simple, too. Span resistors will be connected between A+ and A- or B+ and B- terminals on the lower left side of the I/O subpanel. If there is more than one span resistor, be sure you are checking the correct one for the analog in question. With the voltmeter still set to read DC put the red lead on the + side of the resistor and the black lead to the - side. The voltage measured here will be in millivolts. The amount of millivolts will vary from system to system. A good rule of thumb is to measure the voltage across the span resistor when the tank or pressure is low and again when it is full or high. Write down these measurements to refer to later when troubleshooting.
The transducer, span resistor and offset resistor (if applicable) is all wired in a ‘series’ connection. The output of the transducer sets the amount of current that will flow through this series circuit. This set amount of current causes a voltage drop across the span resistor. The onecard measures the voltage across the span resistor, converts it to digital form and sends this value to the pump station or central for display.
If the current is high, the voltage drop across the span resistor will be too high for it to measure. This is called ‘saturation’. A sure sign of saturation is not being able to get the calibration voltage below 5 volts DC.
If saturation occurs, the offset resistor is added to the series circuit. The offset resistor drops some of the extra voltage, thus lowering the amount measured by the onecard. Sometimes an offset resistor is already placed on the offset terminals with a jumper in place behind the resistor. To put the resistor in the circuit, remove the jumper behind it, leaving the resistor in place.
Using calculations
in place of measurements
An alternative to measuring the amount of current a transducer is putting out is to calculate it. Use this equation:
millivolts measured across span resistor divided by resistor value = current
For example, a 2.53 ohm resistor has 10.5 millivolts across
it. .0105 divided by 2.53 = .00415. Remember
that millivolts and milliamps are less that 1
unit. Milli means the first three places to the right of the decimal
point.
Example: 18 milliamps can be shown as
.018 . 15.3 milliamps will be
shown as .0153 .
AC voltage measurements are as simple as DC measurements, except the danger of getting shocked is much greater.
!Always use extra care when making any AC voltage measurements. For voltages greater than 220 volts AC, have a certified electrician do the testing for you. For example, if your body makes contact with 480 volts AC, you make not be able to pull yourself away from it . This of course, could have disastrous results.
To measure AC voltage, set the meter to read AC volts. Unlike DC, it does not matter which meter lead goes to the measuring point and which goes to neutral. Touch one lead to the point to be measured while touching any point marked neutral. White wire is used for neutral in 120 volt AC systems in the United states. Black wire is used for Hot (also sometimes called line or L1). Always use caution not to let the meter lead touch (short) to something else when touching to a Hot point.
When checking AC voltages, ground should be the same as neutral. It is very good practice to put the voltmeter between a grounded point and a neutral connection to see if any voltage is present. Less than 1 volt should be acceptable. If you see more than 1 volt, contact your utility company or Micro-Comm for instructions.
II. Current Measurements
We have talked about the fact that a transducer is a device that with a voltage applied to it, it will output current that changes based on the amount of pressure applied to the transducer. If you are uncertain about using a meter to measure current, See appendix E, How to Use a Voltmeter for more information.
First locate the wires (cable) coming from the transducer in question. With the meter set to measure milliamps, disconnect the red wire from +14 and put the red meter lead on the +14 terminal. Put the black meter lead on the red wire from the transducer. With power ON and pressure on the transducer, the meter will read somewhere between 4 and 20 milliamps of current. Using this measured current, you can calculate how much pressure is on the transducer and shown in appendix A: A closer look at transducers.
III.
Fuse Checking Procedures
Typically fuses are checked by doing a continuity test. A continuity tester (or meter) touched to the ends of the fuse will tell you if it is internally connected. This is pretty reliable, however sometimes a fuse will open internally when it is placed back into the circuit with power applied to it. Also, just putting in the fuse holder can flex it enough to open the internal connection. This can cause a lot of grief after you have checked it out of the circuit thinking that it is good.
There is a good way to check a fuse while it is in the holder and under power. Using a voltmeter, place the black meter lead to ground and touch the red lead to each end of the fuse. The voltage should be the same on both ends of the fuse. There may be a very slight (less than ½ a volt difference) between the readings, which is acceptable.
For example, if the fuse is in a 12 volt circuit, you should see approximately 12 volts on both ends of the fuse with respect to ground. If you see 12 volts on one end and zero on the other, then replace the fuse.
To test fuses using this method, set your voltmeter to read DC volts when testing the radio, battery and onecard fuses. Set the voltmeter to read AC volts (120) when testing the power supply and line filter fuses. Note that the newer line filter fuse (screw in type) cannot be accessed to do this test.
Make DC measurements with the black meter lead on any terminal marked PRG. Make AC measurements with the black lead on any terminal marked NP. Put the red meter lead on the fuse whether it is AC or DC.
If
you have doubts about a fuse, replace it anyway.
6. Troubleshooting
procedures
So far we have covered the components in the system, tools, and other knowledge needed to perform basic troubleshooting within the Micro-Comm system. Now lets get ready for problem solving. The following section shows the most common symptoms to verify the type of problem. The upcoming section shows things to check after the type of problem has been verified.
I. Symptoms of common problems
Loss of Signal
Symptoms of a loss of signal condition:
1. Display at pump station shows only a - (dash) or E
2. Telemetry Control lamp at pump station RTU is OFF
3. Telemetry Control lamp at tower RTU is OFF
4. Displayed tank level does not change
5. PDU shows LOS
Faulty transducer
1. Displayed level is erratic
2. Chart recorder is spiking
3. Pumps are short cycling
4. False low tower level alarm
5. False high tower level alarm
Control valve failure
1. Control valve FAIL alarm
2. Pumps will not shut OFF
3. Stem on control valve will not move up or down
4. Water is constantly leaking out of the drain tube (if applicable).
Pump motor control center failure
1. Pump FAIL alarm
2. Pumps will not start in HAND
3. Pump station phase or power fail alarm
Air trapped in
transducer sense line
1. Erratic tower level
Dirt or debris
trapped in transducer sense line
1. Erratic tower level readings
2. Constant low or high tower level readings
Faulty calibration
pot on RTU main panel
1. Erratic tower or pressure readings
II.
Problem solving
The following section gives you things to check in order until the problem is found. In some cases, the exact cause of a problem cannot be determined until the suspected part is tested at Micro-Comm’s in-house facility. In this case, you can put an identical part into the RTU from another operating RTU, which is covered in this section. The questionable part then is sent back for testing.
Loss of
Signal at a single remote site
1. Make sure antenna is in place, pointing the correct direction. Inspect the coax and make sure it is not damaged, twisted, unconnected, or loose from its mounting (tape).
2. Use continuity meter to make sure the center conductor is not shorted to the outer conductor (shield). Another test is to check continuity from the center conductor to the driven element (the one mounted through the white insulator) on the antenna. The easiest way to do this is clip lead the driven element to another element on the antenna. Then check for continuity between the center conductor and the shield at the radio end. Do all coax continuity tests through the end closest to the radio, that way you will find shorts or opens in the patch cord and lightning arrestor as well.
3. Test incoming 120 VAC power. The light in the line filter should be ON. Test this voltage on the DC power supply fuse (which is the 120 VAC input to power supply) with reference to ground (lightning arrestor or neutral terminal). Anything measured within 10% of 120 VAC is acceptable. This will show that incoming power is getting to the DC power supply.
4. Check output of DC power supply. The small board on the power supply has two ¼ inch tall posts with red and black wires connected. It may also have + and – on the board as well. Use DC voltmeter on these posts to verify the supply is putting out about 13.8 VDC. The 13V lamp on the subpanel should be on.
5. Make sure all coax connectors within the panel are clean and tight. Check all other plug in and screw terminals as well.
6. Listen to the radio and watch the transmit light on the radio for a few minutes. The lamp should come on (or change colors) briefly when the radio transmits. The radio should be silent while it is transmitting. If the radio does appear to transmit, then replace the onecard. The onecard may be transmitting erroneous data. Another way to verify the radio is transmitting a signal, is to program a hand held scanner to the frequency printed on the side of the radio. When the transmit light comes ON, you should hear what is being transmitted through the radio
7. If the radio does not appear to transmit, then change the onecard as it may not be keying up the radio. If this does not fix the loss of signal, try changing out the radio.
8. Coax connection at the
antenna may be poor. The center pin of the coax connector that goes into the
antenna connector may be mis-aligned. If this has happened, the female
receptacle in the antenna connector may be broken. This can be found by
unscrewing the coax connector from the antenna and looking inside the antenna
connector. If the split brass tube inside the connector is spread out or if one
of the tulips is broken, then the antenna must be replaced.
Note that the patch cord and lightning arrestor may not show bad while you are testing the coax connections. For example, the patch cord may be shorted only when it flexes as the RTU door is closed. If there is any doubt about the patch cord or lightning arrestor, replace both.
Quick checklist for Loss of Signal diagnosis:
1. antenna is missing
2. antenna is turned the wrong way
3. antenna is missing elements
4. antenna coax is cut or shorted
5. antenna coax has loose or dirty connector
6. moisture in antenna coax
7. corroded coax connector (at radio, patch cord, lightning arrestor and antenna)
8. blown radio fuse
9. blown onecard fuse
10. blown power supply fuse
11. blown line filter fuse
12. tripped breaker
13. line filter is turned off
14. patch cord is loose at the lightning arrestor
15. radio is turned off
16. faulty lightning arrestor (open or shorted)
17. faulty patch cord (open or shorted)
18. faulty power supply
19. faulty onecard
20. faulty radio
21. faulty ribbon cable connection to radio, onecard or power supply
22. faulty I/O subpanel
If in doubt, do the following:
1. Replace the onecard with one from a working site.
2. Replace the radio with one from a working site.
3. Replace the patch cord with one from a working site.
4. Replace the lightning arrestor with one from a working site.
Random loss of signals at
more than one site (pulser)
For the telemetry system to operate properly, each RTU radio must be able to transmit its signal and be heard by its associated site every few minutes. There have been provisions made so that in the event that one or two successive transmissions are missed, the system will still continue to operate normally.
If a transmitter within the Micro-Comm system transmits at random, the signals may block out other signals for more than two successive transmissions. In other words, two radios may be transmitting at the same time which will cause other radios not to receive properly (causing a loss of signal condition). A sign that two radios are transmitting at the same time is that the telemetry tones will sound skewed or otherwise unusual.
Also, because each RTU transmits at a slightly different moment in time, the loss of signals can appear to move around the system.
The RTU that is transmitting at random is called a pulser and the most likely cause is a faulty onecard. Finding which site is the pulser can be difficult, but following these steps should make it easier:
1. Go to each site in the system. Increase radio volume and listen for the telemetry tones. If you hear tones that sound skewed or off pitch, go to the next site.
2. Continue going to each site and listening to the radio. The one site where you DO NOT hear the skewed tones is probably where the problem lies. Change the onecard at that site and the problem should be solved.
Also note that you may see the radio transmit light come on more often or be on longer. This can be an indication that you have found the pulser site.
Pump control problems
Control problems within a pump station can stem from one of two causes:
1 - The automatic telemetry control is not functioning properly.
2 - The motor control panel is not functioning properly.
The key to
troubleshooting a pump station problem is to determine which one of the two
above mentioned possibilities is the culprit. If the pumps will start in HAND but not in AUTO, then possibly there is
a problem with the telemetry control panel. Check these things:
1. See if tower or pump station is in loss if
signal. A tower loss of signal will show as an E or - (dash) on the pump
station display. If the pump station is in loss of signal, the telemetry
control lamp will be OFF. See the Loss of
Signal Troubleshooting section for more information.
2. Check to see if the time delay relay for the pump call is coming ON. Be sure to watch it long enough to see it time out and close its contacts. When it times out and the contacts close, the call lamp should come ON and the pumps should start. If the relay does not come ON, replace it. If the relay and the call lamp do come ON, but the pump does not start, then the problem possibly lies within the motor control panel. Have a certified electrician take a look at the motor control panel.
3. If the time delay relay has been replaced and still will not come on, check all fuses, DC power supply and incoming AC power to the telemetry panel.
4. If all fuses and power supplies test ok, change the onecard and onecard ribbon cables.
5. Replace the
I/O subpanel. This may require assistance from Micro-Comm personnel.
If the pump will not start in HAND, check these things:
HAND is supposed to start the pumps immediately with no conditions. When a pump won’t start in HAND, that indicates a problem within the motor control panel. This could be a tripped breaker, blown fuse, burned wiring, tripped overload, tripped phase monitor, burned motor winding, high discharge or low suction condition.
! Always have a certified electrician perform testing and repairs within a motor control or any high voltage panel.
Electrical wiring within a pump station can be very confusing. For example, the high discharge cutoff switch may be located in the telemetry panel not the motor control center. Most of the time these devices mounted in the telemetry panel will have accompanying lights to give you visual status. When in doubt, call Micro-Comm service for instructions.
Chart recorder malfunction
Chart recorder problems stem from one of two causes:
1. Electrical signal going into the recorder is incorrect
2. Chart recorder unit has internal problem
Most Honeywell chart recorders supplied by Micro-Comm use a 0-5 volt DC input signal. This signal is directly proportional to the displayed scale. For example, if you are using 0-25 scale chart paper, then 0-5 volts input is equal to 0-25 feet charted. In rare cases, some recorders use another type of input signal such as 4-20 mA or a pulse. If your recorder has one of these types of input, contact Micro-Comm for assistance.
Chart recorder
spiking
Typically, if the recorder is erratic (spiking up or down) then the input signal source is the problem. This indicates that the chart recorder is functioning normally and the problem may lie with the device (transducer, etc.) that is being charted. Refer to Transducer Troubleshooting section for more information.
Chart not turning,
pen frozen or pen not moving to correct position
If the chart sheet is not turning, or stops at random, verify that the recorder unit is not losing 120 volts AC power at random. If the power normal, try replacing the chart motor and main controller board.
If the pen does not go to the correct position, use
voltmeter to check the incoming 0-5 volt DC signal. Remember that 0-5 volts =
0-full scale. For example, if you measure 2.5 volts on the input, the pen
should be halfway up the chart. Likewise, zero volts will put the pen at the
bottom and 5 volts will put it at the top of the chart. By checking this voltage and comparing it to the position of the pen
you can determine if the problem lies in the recorder or the signal.
If you determine a signal problem, try changing the onecard at the RTU where the recorder is connected. If this does not work, go directly to the source of the level being charted (transducer, etc.). Remember, the source may be from another RTU at another location. Refer to Transducer Troubleshooting for more information.
If the signal appears to be correct, change the chart recorder pen motor and main controller board.
Transducer Troubleshooting
As previously mentioned, a faulty transducer can show in a variety of different ways. Erratic displayed levels, erratic chart recorder readings, zero readings, pumps not coming on or shutting off are to name a few. Before determining that a transducer is broken lets cover a few other things:
1. Is air trapped in the transducer connecting line? The compression of air can cause erratic readings. Remedy by bleeding off the air.
2. Is dirt or debris caught in the connect line or inside the transducer itself? Water does not constantly flow into the transducer. Over time, sediment will settle in the lowest parts of the connect line. Likewise sediment can collect inside the transducer itself hampering movement of the pressure diaphragm. Flushing the line and transducer will help. Also mount the transducer so the connection line is down. This will help keep sediment from building up on the diaphragm.
3. Are electrical connections to the transducer clean and tight? A loose or corroded wire can cause erratic readings that may be temperature related. In other words, the connection may be good when it is warm but go bad when is cools off (night). Tighten electrical connections both at the transducer and the RTU.
NOTE-In some cases water has gotten into the transducer cable. The cable will ‘wick’ the water towards the ends. Unfortunately, the transducer is at one of the ends. Water inside the electrical part of the transducer will short it out.
If you have done
the above steps and the level is still incorrect or erratic
Troubleshooting hints and summary
When troubleshooting, it is a good idea to check everything in the RTU-even if it is not related to this specific problem. The reason being that you might uncover a future problem or a problem you have not yet discovered. For example, if you have a loss of signal or a faulty transducer, always do the following while at the RTU:
Check antenna condition and direction
Check fuses for the onecard, radio, line filter, battery and DC power supply.
Measure incoming power
Measure DC power supply voltage
Test and monitor calibration voltage
Check coax connections-make sure they are clean and tight
Sometimes lightning damage is not so obvious. Look along the bottom back of the RTU enclosure just below the I/O subpanel circuit board for black streaks of carbon. Metal traces on the back of the board can melt, falling down to the bottom. If you see this, lightning may have damaged the backside of the board and it will probably have to be replaced.
The Line Protection Unit (also called line filter) may look smoky inside after a lightning hit. Although it may still function, it should be replaced.
RTU’s are subjected
to a lot. Extreme heat, cold, lightning and corrosive environments. Coax connections, plug in terminals and
calibration pots may become internally corroded over time. This can result in
loss of signals and erratic level readings. Sometimes just changing a part will
loosen or scrape the corrosion enough to make a good connection. Now, you
have just changed a part thinking the one that came out is bad when in fact its
not! This is why we at Micro-Comm get a lot of parts in for repair that are not
broken. We highly recommend that the suspected part be put back in place to see
if the original problem can be duplicated. If the part is indeed faulty, sent
it in for repair.
Refer to section 2-II Preventative maintenance calibration procedures for more information.
Other things to think about
Most of the time there is an explanation why an RTU is not working correctly. Good examples are lightning, freezing temperatures, high winds, vandalism or someone damaging the RTU by accident. Some things can change over a period years which can cause problems, too. Some things to consider:
1. Do the telemetry tones sound crisp and clean?
If they sound skewed or the volume seems to be low, then the radios may need to be sent to Micro-Comm for a checkup. Like your car, a radio may need to be aligned (tuned up) after several years of operation.
2. Are loss of signals less frequent in the Fall and Winter?
As discussed earlier,
if a radio signal path is weak, leaves on the trees during the Spring and
Summer can cause loss of signals. If you have this problem contact Micro-Comm
for an evaluation if the radio path.
3. Have loss of signals been more frequent since new construction near the RTU?
A large structure
built directly in front of the RTU antenna could be the problem. In very rare
cases, other antennas placed on the tank (cellular phone, police department,
etc.) can cause interference. This is usually easy to pinpoint because the
telemetry will interfere with them, too.
4. Has
any unauthorized person had access to the RTU or to other electrical panels
that are connected to the RTU?
As mentioned above, sometimes someone working near the RTU will accidentally turn off the power, create an electrical short or otherwise might damage to the RTU. Always check to see if anyone else was working on or around the RTU. For example, someone working on the motor control center might accidentally short together wires that come into the RTU.
5. If your RTU does not have battery backup, the utility company supplying power may be having intermittent problems that are causing the RTU to go into loss of signal at random.
It is not uncommon for an RTU to be on the end of a dirt road on its own electrical service. With no other customers on that service and the power goes off occasionally, it can be difficult to prove it. However, most utility companies are good about working with you to find the problem.
Good advice: Some
problems come and go. They are hard to find when the RTU appears to be working
correctly when you are there. Keep this in mind:
Even if you don’t suspect another part of the RTU, check it anyway. Make it a point to always
check incoming AC voltage, DC power supply voltage, span resistor voltage and all fuses when
diagnosing any problem. You might
find something unusual that is causing the problem or be able to prevent
another one down the road. Also, if problems happen during a particular time of
day or with a weather change, make notes of time and condition.
Appendix
Appendix A: A closer
look at transducers
Transducers are sized based on their maximum rated pressure . For example, for a tank 120 feet tall, a 60 psi transducer would work best. Say the transducer was five feet under ground, 125 vertical feet of water is 54.1 psi on the transducer (125 divided by 2.31). Transducers can be broken if they are over pressurized.
Likewise, it is overkill to put a 300 psi transducer on a suction line that will never go over 50 psi. Keeping the transducer closely matched to the actual measured range also helps to enhance resolution.
Standard transducer sizes are 15 psi, 60 psi, 100 psi and 300 psi.
To determine how much pressure is on a transducer based on how much current it is putting out:
The calculation is shown as:
Measured current subtract 4 = X
X divided by 16 = Y (percentage)
Y multiplied by transducer size = psi on the transducer
For example we are using a 100 psi transducer. Its measured current output is 9 milliamps. Take current output and subtract 4. This will give us 5. Take this number and divide it by 16. This will give us a percentage of .3125. Multiply .3125 times the full scale of the transducer which is 100. This gives you the pressure that is on the transducer which is 31.25 psi.
To calculate vertical feet of water on the transducer, simply multiply psi times 2.31.
Using the above calculation works well to determine how much water is in a tank. When doing this, remember that the transducer is usually located below the bottom of the tank. Remember to subtract how deep the transducer is in the ground from the calculated reading. For example:
The tank is 120 feet tall. The transducer is in the ground 6 feet below the bottom of the tank. Your calculations showed 95 vertical feet of water. 95 subtract 6 equals 89 feet. With 89 feet of water in a 120 foot tank, it is 31 feet from being full.
Appendix B: More about span resistors
A span resistor sets the usable range (or scale) in feet used for this particular tank. For example, an elevated tank might be on a 0 to 25 foot scale, thus measuring the usable top 25 feet of the tank. In short, the span resistor provides a small ‘window’ (0 to 25 feet) of the usable range of the transducer.
Current from the transducer passes through the span resistor causing a voltage drop across the resistor. The onecard measures this voltage, transforms it to digital form and sends it to the central or pump station for processing.
The calibration adjustment in the RTU simply provides offset voltage in the circuit to move the span resistor window up and down the tank. When an RTU is calibrated to 5 volts DC while the tank is overflowing, the top of the 25.5 foot window is even with the top of the tank.
Span resistors a high precision type and are usually have very low resistance ratings (2.53 ohm, 5.06 ohm, etc.).
Appendix C: Calibration of a tank that is not full
The output of a transducer can be used to figure how much vertical water is above it (refer to Appendix A for calculations). However, there are other ways to figure how much water is in the tank. Sometimes an accurate pressure gauge can be used. Simply multiply its reading times 2.31, taking into account any elevation differences. Another way to do it is have a brave soul climb the tank and check the level with a tape measure. Regardless of how you determine the level in the tank, we can now calibrate the tank level using the following calculations.
Tank scale minus how far from full = x (feet)
x divided by tank scale = Y (percentage)
Y multiplied by 5 = voltage setting
For example the tank is on a 0 to 51 foot scale. Say the tank is 10 feet from being full. 51 subtract 10 is 41. 41 divided by 51 is .8 . Multiply .8 times 5 and you get 4.00. 4.00 volts is where you need to set the calibration test voltage.
The RTU will send back a reading of 41 feet.
Again, you can use simple algebra in this equation: 0 to 5 volts calibration voltage is equal to 0 to Full Scale!
Appendix D: Calibration of discharge and suction pressures
This is done much like calibration of a tank when it is not full. Lets go through the calculations:
gauge pressure divided by transmitted scale = X (percentage)
X multiplied by 5 = calibration voltage setting
For example the transmitted scale is 0 to 255 psi. The gauge reads 73 psi. 73 divided by 255 equals .286 . .286 multiplied by 5 equals 1.43 volts. Set the calibration voltage to 1.43 and the RTU will transmit 73 psi.
Appendix E - How to Use a Voltmeter
To measure AC voltage, set the meter dial to the next higher range than what you want to measure. For example, if you want measure a 120 Volt AC line and the meter has settings of 100 VAC, 200 VAC, 400 VAC, then set the meter to the 200 VAC range. Note that most modern voltmeters have an auto ranging function where you change it to the AC setting, and the meter automatically sets the range. When measuring AC it does not matter which meter lead is connected where. Most AC measurements are made with one lead on a HOT connection and the other lead to a NEUTRAL connection. The meter display will show the voltage. Always use extra care when making AC voltage measurements!
To measure DC voltage, use the same setting procedure as above, only with the DC settings on the meter dial. Note that the black meter lead needs to go to the (-) connection, and the red lead to the (+) connection.
DC voltages less than 1 volt are measured in milliamps. Set the meter dial accordingly. Then display may read with numbers to the right of the decimal point .021, which would be 21 millivolts. Millivolts go up to .999 making the next step be 1 volt even.
Fortunately, most newer meters will display a whole value like 21 and say the word millivolts next to the number, thus making it easier to read.
To measure current, set the meter to read in AMPS or if it has a setting, to MILLIAMPS. Disconnect the (+) wire to the device in question. Put the red meter lead to the point where the wire was previously connected. Put the black meter lead on the wire. The display will show you how much current the device has going through it. !USE THIS PROCEDURE FOR TRANSDUCER CURRENT MEASUREMENTS ONLY. DO NOT ATTEMPT TO MEASURE CURRENT ON A HIGH VOLTAGE AC DEVICE. REFER TO QUALIFIED PERSONNEL FOR HIGH VOLTAGE/CURRENT MEASUREMENTS.
Appendix F - What to do if calibration voltage stays
higher than 5 volts
If the calibration voltage cannot be adjusted below 5 volts by turning the calibration adjustment more than 20 turns either direction, then an offset resistor will need to be installed. Offset resistors are usually only needed when a different size of transducer has been installed. Note that a different size of transducer will require a different span resistor. Contact Micro-Comm before going to a different size (15 psi,60 psi, 100 psi or 300 psi) transducer.
To install an offset resistor, locate the offset resistor terminals on the I/O subpanel ( they are next to the calibration test points). In most cases there is a resistor already installed in the terminals. Also installed in the terminals is a piece of jumper wire behind the resistor. Use a screwdriver to loosen the terminal screws, then remove the jumper wire leaving the resistor in place. If a resistor is not already in place, you can install a ¼ watt, 10kohm resistor which is readily available at electronic shops. If the 10kohm (10 thousand ohms) doesn’t do the trick try something closer to a 5kohm or go up to a 15 kohm. If you have a resistor that has a value within a couple of thousands of ohms of what you want, it probably will work. It is ok to experiment with values.
Appendix G - More about signal paths
The strength of a path signal path is measured in decibels (also called db). How many units of decibels is also called pad. The more units of pad, the less problems there will be with loss of signals. A good path will have more that 36 db of pad. A marginal path may have only 20 db of pad. Anything less than 20 db is considered poor. Also, the higher the radio frequency, the more pad required. This means a VHF radio might work fine with a 20 db path, where a UHF radio might have difficulty with the same path.
A path with more than 36 db of pad will probably not have any problems due to ice on the antenna. A path with less than 20 db will probably have loss of signal problems with the same amount of ice. Things that weaken a radio signal path include foliage, buildings, distance, ice and antenna damage. Weather and sunspots (solar activity) may affect signal paths that are already weak.
Glossary of terms used with a
Micro-Comm telemetry system
AC (voltage) - AC stands for alternating current. Alternating current changes from a positive voltage to a negative voltage (polarity) many times a second. AC was developed so that power could be sent long distances without major line losses. AC voltage is associated with a frequency (measured in hertz) that it changes polarity. The standard for this frequency in the United States is 60 hertz. In other words, AC power changes polarity 60 times a second. Hertz is also called cycles.
Analog - Where digital is like a light switch, either on or off, analog is like turning a spigot for more or less water. For instance, a pressure transducer can vary its output (tower level) based on the amount of pressure applied to it. Analog is sometimes called a variable signal.
Baud Rate - Usually associated with a number, baud rate is the speed at which data is sent from point to point. Typical radio baud rates are 110, 300, 600 and 1200. Common computer baud rates are 1200 and higher. Also referred to as baud and baud speed.
CPU - Central Processing Unit. The point at which all input/output processing and decision making is made. A CPU typically is controlled by a microchip processor programmed by factory personnel.
DC (voltage) - Stands for direct current. Unlike AC voltage, the polarity of DC is always the same. It is always associated with + (positive) and - (negative) polarity. DC works well to simplify small circuits.
Debug Terminal - A hand held computer that is plugged into an RTU for testing purposes. Most all functions of the RTU can be tested with this terminal including checking address, flow rate information, input status, output control, scaling factors and viewing the radio communications.
Dry contact - Dry contacts mean switched contacts that are electrically isolated from any other circuits. A dry contact is usually the same as the switching contacts on a relay. A power source turns on the relay, switching a different power source through the relays contacts, thus turning on a device.
Input - A point where a device is connected to an RTU to provide data. Common devices connected to inputs are pressure switches, temperature switches, transducers, flow meters, etc. For devices that provide an off or on type input only, this is sometimes called a discreet input .
LCD Display - LCD stands for Liquid Crystal Display. A very popular type display due to its low power requirements and durability.
Motor Control Center - Panel located near the pumps that houses starter contactors, fuses, control circuit wiring, relays and circuit breakers used to switch incoming power to the pumps. Hand-Off-Auto switches are usually on the front of this panel. In some cases the electrical disconnect for the motor control center is built into this panel or in an adjacent panel. HIGH VOLTAGE can be present within the motor control center. Refer service to qualified personnel.
OneCard - A white plastic box, approximately 3” tall x 7” long x 4 ½ “ wide used in RTU’s. A OneCard contains a CPU and controls all aspects of the RTU. There are a few different types of OneCards, which are covered section 2 Components within the Micro-Comm Telemetry System.
Open - (electrical) when a circuit is disconnected it is considered open. No current will flow through the circuit. For example, turning off a light switch opens the circuit.
PDU - Portable Data Unit. A hand held device that utilizes a palmtop computer and radio receiver to display levels, alarms, pump status and flow rate
information. A PDU listens to the system 24 hours a day at home, in the office or a vehicle.
PTU - Portable Terminal Unit. Exactly like a PDU, except has a radio transmitter built in as well. A PTU can send signals to silence alarms, restart pumps, close valves, etc.
RTU - Remote Terminal Unit. An RTU is a telemetry site that has a specified number and type of inputs, outputs and analogs . Radio type RTU’s would include water towers, ground storage tanks, pump stations, wells, master meter pits and pressure monitoring points. There are also embedded type RTU’s at a central site that are hardwired to the central for plant control. Note that all RTU’s each have a unique two letter address. RTU’s are also sometimes called stations or remotes.
Short - (electrical) a short can be caused by a faulty component. When the component fails, it may pull more current from the power supply than normal. A fuse placed between the component and the power supply will blow, protecting both from further damage. In some cases a device (such as a flowmeter) may not be fused. If that device develops a short it may pull down the power supply causing damage to both components and any connections between them. Fortunately, low voltage DC shorts rarely result in serious damage.
UHF - stand for Ultra High Frequency. Micro-Comm frequencies used in this band are normally between 451.000 mhz and 456.000 mhz.
VHF - stands for Very High Frequency. Micro-Comm frequencies used in this band are normally between 154.000 mhz and 173 mhz.
Post warranty
information
As you may have already found, the warranty that comes with your new Micro-Comm telemetry system is invaluable. Under warranty we can help you save down time by issuing an RMA (Return Material Authorization) number for the part being returned and ship a replacement part to you for free. The new part stays with your equipment while the returned part is repaired and stocked.
Length and type of new equipment warranties can vary mainly due to contract specifications. For out of warranty customers we issue RMA numbers and perform repairs the same as our warranty customers. Needless to say, after the warranty expires your maintenance costs may increase as we can only sell parts and perform chargeable repairs for our non-warranty customers.
The simple
solution to reducing these costs is a Micro-Comm Extended Warranty/Service
Contract. Upon purchasing this contract, there is no cost for parts, plus a 33%
savings on labor expenses should a trip be required.
If you are not sure when your warranty expires or if your system is already out of warranty, give us a call. We’ll quickly get you the information you need.
Remember-whether under warranty or not, our phone tech support service is always 100% free!
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