Glossary of terms used

Abbreviations and specialized terms are often used in the SCADA industry. Below is a list with explanations of those used in a Micro-Comm SCADA system:

Analog- A variable signal, generally a voltage or current. Analogs are commonly used for precision measurements regarding levels, pressures or flows. From the Micro-Comm perspective, an analog input is where another device supplies a signal to a Micro-Comm PLC. An analog output is where the Micro-Comm PLC supplies a signal to another device.

Baud rate- The speed at which data is sent throughout the radio system. Common baud rates used are 110, 600, 1200 and 2400. Bandwidth directly affects baud rate; in a licensed radio system FCC rules may restrict bandwidth, which in turn can affect what baud rate can be used.

CTU- also sometimes referred to as a Central. CTU is an abbreviation for Central Terminal Unit.

Discrete- An on or off signal. From the Micro-Comm perspective, a discrete output is where we close a contact, which closes the circuit to turn on a pump, valve or other. A discrete input is where another device closes a contact to turn on our input, giving a run or similar status. An example would be where the Micro-Comm PLC closes a contact on a discrete output to start a pump; in return, when the motor is running, the motor control center provides a similar contact back to the Micro-Comm PLC discrete input for a run indication.

Licensed radio system- Where a frequency is licensed for the exclusive use for a SCADA system. A licensed system offers some legal protection in the event of interference by another radio system.

Loss of Signal- The SCADA system will make a predetermined number of attempts to communicate with an RTU/PLC. If the unit does not respond during any of those attempts, a Loss of Signal alarm is generated. Note that if it responds intermittently inside this window of tries, the Loss of Signal alarm will not be generated. However, you will see increased times in the ‘last heard from’ or ‘data age’ screens. Increased times are a sign of a pending issue that may eventually result in a total Loss of Signal condition.

PAD- A term used in reference to excess radio signal strength. PAD is often ‘built in’ to a radio system to insure that the system will continue to operate reliably even when the signals are degraded by weather, atmospheric conditions, buildings, trees or other objects that may interfere with the radio path.

Radio path- Signal strength and other factors directly between two sites that communicate with each other. In designing a SCADA system, a radio path study is done prior to installing any equipment to insure that all signals between sites will be reliable under a variety of conditions.

RTU- Remote Terminal Unit.

PLC- Abbreviation for Programmable Logic Controller. PLC’s are manufactured by a variety of companies including Micro-Comm.

Port forwarding- In regard to using a web page to monitor your Micro-Comm SCADA system, the web page is broadcast from the host computer to the outside world through an internet connection. This connection is typically through the use of an internet router. Since most routers by default do not allow the broadcast of a web page, the router must be manually configured to allow the web page to be broadcast to the outside world. Port forwarding is a common term used to change settings in the router to allow the web page to work. NOTE- It is very common for the internet provider to physically replace the router or reset it to factory settings without notice. This in turn will erase the settings that allow the web page to work, meaning it will need to be reconfigured.

Pump/valve fail- After giving a call to turn on a pump or valve, the SCADA system starts a timer which gives the pump or valve an amount of time to provide a run or open condition. If the pump or valve does not give a run or open, the system will generate a fail alarm. Note- when a fail alarm is generated, the SCADA system typically turns off the output and stops calling the device until the problem is resolved.

SCADA- Supervisory Control And Data Acquisition

Server- A primary computer often used as a central point of control. In some cases it will feed data to other computers on a network.

Telemetry- A term previously used, which has been essentially replaced with the SCADA acronym. Telemetry by definition is the sending of digital tones on an analog type radio; the tones then are transcribed by the system into a series of numbers and letters.

Unlicensed radio system- Commonly high speed ‘spread spectrum’ radios are used in an unlicensed radio system. The radios are designed to avoid interference with adjacent systems; however, in the event of interference, the two entities are without FCC recourse and must individually make changes/adjustments to solve interference problems.

Yagi- A type of directional, high gain antenna commonly used in SCADA systems.

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