475 HART Communicator Disconnected when Simulated the 4~20mA


Thread Starter


Hi everyone,

I have a transmitter EJA110E using HART communication. So when I used 475 communicator to connect to the transmitter and simulated a loop current from 4~20mA. I could simulated 4-15 mA but when I increased 17-20 mA, 475 HART Communicator disconnected.

I used 475 HART Communicator to connect to EJA110E.

Thank you
Dear dsony,
Please check the voltage on the channel. It should be not less than 22V on 4mA and 16.5V on 20mA. The best solution is to compare voltage with another channel where the same transmitters are installed.
When the total resistance in the loop exceeds what the power supply voltage can drive current through, then the transmitter's output drives current up to the point the voltage supports, then faults in some mode.

I saw this in action the transmitter repeatedly attempted to re-intialize (go through the start-up routine).

If this is how a Yokogawa reacts to insufficient voltage (for the loop's resistance) then the 475 would not be able to communicate to the transmitter because the transmitter was not in operational state, it would continuously attempting to get there.

Here's a chart of the voltage versus loop resistance for the EJA:

If the loop resistance was high, say 250 ohms at the AI, an I/S barrier, a long run of small gauge wire and you added the loop resistance module on the 475, you might have exceeded the ability of the power supply to power the loop through its entire current range.

If you have used that resistor module on the 475, try taking it out and connecting without it.
Thank you all,

The cause was indeed from power supply. I used a external power supply 24V and it's OK. But when I tried 12V power supply, the same symptoms happened. So, we are investing the power supply.