Heiko Epkens 2 years ago in Master modules / MC4x updated by Gustav Widén (System support) 2 years ago 1

Hello.  I am testing my MC41 application using a Eurtherm G-438 ( https://www.farnell.com/datasheets/1658070.pdf?_ga=2.178838692.143399012.1654225772-1786236872.1616697046&_gac=1.2754052.1650585147.EAIaIQobChMIlfWcop-m9wIVTsLCBB0Krwa-EAYYBiABEgKL5PD_BwE)  signal conditioner to generate a 0-20 mA to simulate one of my inputs.  The MC41 is latching onto a high error and I am puzzled as to why.  I checked the output of the unit and it is in the proper range.  I made a work around using a trim-pot but I want to be sure that I won't have problems when the controller is connected to its real current source.  I noticed that the voltage compliance of the signal conditioner is 12 VDC max whereas my controller is receiving 28 VDC power currently.  Could this be the error?

It sounds as if the Eurotherm device is delivering a current that is higher than the 20 mA it should give out. 

Maybe this happen at startup, so that you do not see this when measuring. 

When the MC4x sees an overload on the Current loop input, it switches out the measurement resistor to avoid damage. After this, you will not be able to measure the current. 

A suggestion is to measure current with a scope, so you can capture what happens at startup.