Honeywell Serial comms to Thermo 4400 Alarm Monitor


Thread Starter


All of our attempt to get these two devices have come to nought. We just need to read the numeric PV values from the monitor.

We have created an HPM array point and can write data to it using a laptop running modbus slave emulator. We can read the pv values in the monitor with the same laptop using a modbus master emulator. But do you think the two devices will talk to each other.

Tried it first on rs232, then went to rs485 both failed. tried different cables (rts/cts etc), baud rates, parity etc. Set up is modbus rtu as that is what the HPM uses.

We have one Thermo 4400 connected vis rs232 to an EPLCG and it works ok. But I dont have another EPLCG that is close so I want to use the HPM.

Has anyone ever seen a Thermo 4400 talking via serial to any sort of device? The thermo manuals and the vendor are of no use.

Curt Wuollet

Set up a datascope program and see what's going across the line, when it works and when it doesn't. Might help. Of course it's more useful when you can change the software. It's that kinda thing that makes OSS so handy.