Interfacing a Temperature Transmitter to a PLC


Thread Starter


Hi there
How does 'smart' temperature and pressure transmitters on the which are fieldbus and Hart compatible interfaced with the input card of the PLC? The input card cards of the PLCs are hardwired while the transmitters are wireless so how are the two interfaced.

A HART or ISA100 wireless field transmitter talks to a 'gateway' which is wireless on one side, wired an Ethernet network on the other.

The ISA100 gateway and the HART wireless gateways put the data from the field transmitters into Modbus slave/server Registers which can be read by a Modbus Master/Client or an OPC server over the wired Ethernet side of the gateway.

To get data to a PLC, an HMI that is a OPC client or Modbus Master/client would read data from the wireless gateway.

There are other (not HART/ISA100) I/O wireless networks that read a field transmitter's 4-20mA signal and provide a 4-20mA signal at the gateway end. But those generally do not use battery powered field transmitters like HART or ISA100, meaning that the field transmitters need to be wired with DC power.