Hello Forum,

I have a Logo 8 and AM2  AQ expansion module which is set up to provide an analogue 4-20mA signal to control a Hoerbiger 4-20mA proportional pressure valve.

When I operate the Logo without the valve connected I am able to accurately control the output within the 4-20mA range, however when I connect the valve the loop current will not drop below 5.2mA.

The analogue control works correctly ( linearly ) above this level.

I have tested the system with two different valves, and two different analogue output modules, but the fault is consistent.

I have also spent a couple of days trying to diagnose the issue with Hoerbiger, but to no avail.

Has anyone experienced a similar issue to this ?

Regards

Jon

J hi there, we have had a similar problem and have solved it. Can you send me your program (zipped) so I can check it over

regards Gerry

Thanks Gerry,

Please find program attached.

Jon

Jon

I have tried a couple of different values:

1k8 - The valve does not operate at all - pressure output 0psi.

5k6 - The "off" state of the loop is much lower, ~1.2 psi at the gauge, where it was previously 8psi, so without measuring the actual current it's obviously much closer to operating at 4mA.

Unfortunately the performance has changed with the resistor in parallel ( to be expected ), and I shall have to check with my customer whether they will be happy with this approach.

Thank you for your help.