Internet PLC Forum

I have started using the FMD88 PLC for the first time and have experienced some anomalies with the analogue inputs. After some fault finding, it looks like some of the channels may be using a different averaging constant. I indentified this as I need to sample AI channels only once after an event where the AI value from the sensor is latched, read by the PLC and then cleared back to 0. When the PLC reads the value I noticed that the values of ADC 4 and 6 were half of ADC3 and 5 respectively when they should be the same and the voltage in to the PLC was correct.

I think this can be explained by the averaging constant being set. This PLC is fresh out of the box and after looking at the AI calibration it looks like values the ADC Calib and the avg constant have been set. What should these settings be when shipped from the factory?

It doesn't look like the averaging constant can be set per channel so I can't understand why some readings are correct and others aren't.

Yes the Vp terminal is connected to 24 Vdc.

The three lights do not turn on and there is no MX-RTC and the RTC.err light stays off

With regards to the thread below...will the FMD series PLC's need the same pin 9 modification?

Is it possible to use Modbus TCP on a F-series PLC as a slave and use send commande using Modbus broadcast mode from the master?

I had a T100MD PLC fail today on site. Upon inspection the only noticible thing was that RTC Error light was OFF. A reset of the PLC didn't fix the issue.

I swapped the RAM chip with a spare I had and the PLC appears as good as new. I'm interested to know what could have caused the RAM chip to fail, as I have quite a few of these PLC's in operation. It has been in service for about 3 years.

I found a laptop with a serial port. Loaded all the Trilogi software on and have the same problem. This would then seem to point to the PLC.

In my second post I noted that the values being read from MODBUS and those shown by the Online Monitor were different. Is this a clue at all?

The jumper is in the ENABLE position and there is no sign of the original program running as the original program turns some outputs on automatically.

The EEPROM appears to work as when I change the program to perform a different output sequence, the PLC retains the program after a power cycle.

I tried this with a different PC today with the same result. Is there any chance it's somthing else, perhaps not PLC related? The only pieces of equipment I can't change at the moment for testing are the USB to Serial converter and DC power supply.

The only thing in the 1stscan CF is the SETPROTOCOL command. Before adding this i didn't even use 1st scan.

The issue is definitely repeatable and I have tested it with another PLC too and the same problem.

I use DAQFactory to poll the PLC and have done so for many years without any difficulties.