Temperature Controller with modbus to CP1L

[rangga.andira 0]

hi all

I want to ask about reading the omron e5ac temperature controller value using modbus to cxp using plc CP1L.. can anyone help?

Thanks

Rangga AW

[DanW 41]

Modbus is a project.  Here's some tips on the Omron end.

1. The spec sheet says that the Omron E5AC uses Modbus RTU over RS-485.  The Omron is a Modbus slave.
Modbus/RS-485 is a communications option, make sure your device's model number decodes as having the Modbus option.
The PLC will need an RS-485 port and whatever firmware it needs to run as a Modbus master.

2. The Omron user manual tells you where to
- select the Modbus protocol (not the Omron CompoWay protocol)
- configure the serial settings for RS-485 (baud rate, parity), which have to be the same on both ends.
- the communications data length (data bits, presumably) defaults to 7, must be changed to 8 for Modbus RTU.
- I recommend 1 stop bit because some devices do not handle two stop bits correctly.
- configure the slave node ID number (Communications Unit No.)
- wire the RS-485, terminals 13 B(+) and 14 A(-).  The Omron lacks a signal ground terminal which can create problems requiring an RS-485 isolator, but try it and see how is works.   Definitions of A/B or (+)/(-) vary from vendor to vendor.  It's supposed to be A to A, B to B, or (+) to (+), (-) to (-), but sometimes the definition is opposite and the A/B wiring needs to be swapped at one end.

3. There is a separate communications manual for Omron devices.  The comm manual will tell you which value is in which Modbus register.

4.  Data formats
Omron calls a 16 bit Modbus register an "element".  
Omron calls a one element, 16 bit integer "two byte mode"
Omron calls a two element, 32 bit floating point values "four byte mode"
Each value has both a 16 integer and a 32 bit floating point value, mapped to different locations, so you can pick which data format is easiest to deal with on the PLC

The data is most likely in 'Holding Registers' that the Master uses Modbus Function Code (FC) 03 to read, or FC 06 or 16 to write values to.

5.  The Omron being the slave is essentially passive once you configure and wire it.  It waits for a command to provide data or change a data value when the command it receives is a Modbus write command.

6. If you're new to Modbus, it sometimes pays to get a generic Windows Master and a USB/RS-485 converter and experiment communicating with Omron with the Windows Modbus master because it is so quick to change settings (don't need to download to make a change).  Modscan, Modpoll or Simply Modbus are the Modbus Masters I frequently see people use.

7.  Get the Modbus comm manual and work on the PLC Modbus master end.