CTU communication fail

A CTU communication fail alarm, also known as PLC LOS, CTU COMM FAIL and DDE Server fail all essentially mean the same thing- the computer is no longer in communication with the CTU. There are many variations that could cause this condition, see below:

Troubleshooting:

The computer may be connected to the CTU in several different ways. In most cases, a power interruption can cause this condition and restarting the computer, completely powering down and back up the CTU will solve the issue. NOTE if there are any ethernet switches or converters between the computer and the CTU, they also will need to be completely powered down and back up to reset them as well.

1. Serial connection. In its simplest from, the computer may be connected to the CTU with a standard serial connection. Typical problems can be a broken serial card on the computer, broken connector or cable, or the serial port at the CTU is broken.

2. Ethernet connection. The computer may be connected to the CTU directly with an ethernet cable, OR it may go through a network connection with an ethernet switch or even a router. Any of this hardware can be suspect in the event of failure. NOTE that Windows updates can often ‘break’ or change settings for the ethernet adapter in the computer.

In some cases, the computer may not directly receive data from the CTU- it may come via a Client/Server type connection from another computer. Check to see if the other computer(s) is getting data or not, this will help to determine where the problem lies.

In other cases, the computer may receive data via a dedicated data radio from another location. If those radios are off or have other issues, this may also cause a CTU COMM FAIL alarm.

Remember, the computer only serves as an interface to the system- In most all cases, if the computer is off line, the system will continue to run on the last entered setpoints. As long as there are no pump/valve failures, etc. that will inhibit operation, the system conceivably could run indefinitely without the computer being on line.

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