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Using Modbus to read data in real time from Chessell chart recorder
Trying to establish channell parameters for a Chessell chart recorder so that values can be read on request

Does anyone have any experience or able to point me in the right direction. Using a Chessell chart recorder with the modbus protocol. I am trying to find out exact parameters in order that i can read specific channels at will the eurotherm manual is of little help here

Thank you

By Michael Erwin on 16 August, 2002 - 10:03 am

We just completed a job with a Chessel recorder using Modbus. It was simple once we figured out the scaling. Our application was a 16 channel recorder. We could read the input data directly from either the 30001-30016 (Channel 1 through 16) or from 40001-40016. The recorder sent raw data of 0 at 4mA input and 32767 at 20 mA. The scaling programmed in the recorder did nothing to the Modbus data.

The Chessel manual includes all kinds of tables that seemed to indicate the data was somehow offset in the Modbus addresses according to the recorder address. It turned out to be completely bogus and just added to our initial confusion.

By Neville Child on 16 August, 2002 - 10:53 am

The comms enabled 4xxx series of recorders from Eurotherm Chessell all use the Modbus RTU protocol.
For Modbus function code 03 or 04. Channel 1 PV is at register 0, channel 2 PV at register 1, etc.

The 5xxx series of recorders have different register ranges.

Please contact me directly for full information

Neville Child
Applications Engineer
Eurotherm Chessell (UK)