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Please help me to understand the AB PLC Modbus mapping. I am talking with a Honeywell TDC3000 through a serial interface. The AB PLC Modbus mapping addresses for analog to in 40001 range. The problem is that I read analog data on this address but it is showing integer value Array. In DCS, how to change this integer value to floating? Can I write Control Language program for it or is some configuration required for it in array? Can anyone help me regading reading this data on Honeywell TDC3000 DCS? Reading of Digital signals is ok.

Best regards,

MUHAMMAD HARIS

Could you give us more details:
- what type of AB PLC you used (PLC-5, SLC, Controllogix, micrologix)

- what brand and type of modbus interface module you have (Prosoft or other brand)

regards

I am using prosoft module for modbus communication

You can always convert any decimal value into an integer by doing a multiplication at the sender and then doing a division at the receiver. For example, if the PLC is requested to send the decimal value of 326.28, then the PLC should multiply it by 100 to become 32628 (an integer), and then the DCS will divide it by 100 to bring it back to 326.28. You must instruct the PLC to do the multiplication, however.

If it is a ControlLogix, then how to read the analog data? Please advise...

Prosoft modules for ControlLogix PLCs use a structure of data with the following parameters (and many others).

MCM.ReadData(i) i=1..240 (typical)
MCM.WriteData(j) j=1..230 (typical)

The PLC programmer must write analog data from PLC to DCS in ReadData array and obtain data received from TDC in Writedata array. Both arrays are real so you can use floating point addressing in the array data points in the TDC side.

The 40,001 range is for integers, try using the 70,001 address range (real numbers). You'll only have 16 inputs per array, instead of 32.

- John