Write UDC2500 high temp limit modbus

[Bmoore14]

Hello!

I am trying to write Modbus TCP to a UDC2500. I keep getting exception code 3(Illegal value) with any register. I am writing from function code 6 - write single register.

I have read the manual several times... I must be missing something.

reg. 40003 working setpoint

ANY help would be greatly appreciated!

 

[NetNathan]

Been there...done that...

You cannot write setpoint across Modbus to a HW High Limit, you can ONLY read.
A High Limit has "FM Approval" which will not allow writing setpoint remotely to a safety instrument.

I assume there are some concerns about remotely writing the wrong information, or comm errors that cause wrong data to be written..

This really bugs me also.....
My work around is reading setpoint and comparing to highest soak in the process cycle and then through the HMI (Intouch), I let the operator know he has to correct the setting.
My advantage here is I am running the process cycle (ramps/soaks) from my PLC logic, so I have access to process cycle data to find highest soak point. I do not know if you have this luxury.

 

[Bmoore14]

Thanks for the response!

In the UDC2500 manual the setpoint register is a R/W register. But this is happening with all write registers.

 

[NetNathan]

The UDC2500 manual is a little generic in Modbus comms across different models. You CAN write the setpoint to a UDC2500 Controller, just not the High Limit.

 

[Bullzi]

In the UDC2500 manual the setpoint register is a R/W register. But this is happening with all write registers.

Are you able to read data properly from the unit? About 90% of the issues with Modbus is making sure you have the addressing correct and byte order correct. After that it is usually pretty easy. If you are not able to write to any register you may be off 1 on your addressing.

 

[NetNathan]

Thanks for the response!

In the UDC2500 manual the setpoint register is a R/W register. But this is happening with all write registers.

What other registers are you trying to write to on a High Limit?