CIN Problems sensing on MC41

James Howland 6 years ago in Master modules / MC4x updated by Codie 2 years ago 12

I am using an IFM Efector 4-20mA 2 wire sensor on the MC41 inputs capable of sensing current.  Their hookup diagram is what I expected connecting one side of the sensor to high and one side to the sensor port.  The input shows a high error when I'm in a neutral state and I can confirm with an ammeter in line that I am sending 4mA to the controller.  My best guess is there is too much impedance and internally it is not correcting for it so I tried adding a 5k resistor to ground externally to split the current.  It now senses 3.8mA but is no longer accurate over the range.  

Resistor to ground with current loop is bad idea...You lose benefits of this interface. If the error is really "high error", but the current is only 4mA, then you need to check the connections and the input settings. Some sensors also indicate the maximum resistance of the shunt with a certain supply voltage, it is worth to look there (the resistance of the MC41 input is 247 Ohms)

I've had the same issue, also a sensor from IFM, only a temperature sensor with a 4-20mA output. Same errors, solution for me was to put a 1K resistor in series with the signal going into the MC41, which solved the problem for me.

Interesting... Which power supply do you use for this sensor and can you specify the part number of the sensor?

No real power supply, only the general power generated by the alternator ±28V

I think we use the TA4105

The formula from the TA4105 documentation ((Ub - 8,5 V) / 21,5 mA) for 28V gives the maximum loop resistance is about 900 ohms...With greater resistance, the sensor can not guarantee coverage of the entire temperature range. I do not know what to say, seems like a sensor problem, but maybe I miss something...

Under review

MC4x CIN input resistance that the sensor will see is 247 ohm.

One function that is good to be aware of is that when you do get a high error on a CIN channel, the MC4x has a protective function that will switch off the connection to protect the sensing resistor. The effect is that the high error will be sticky. 

If there is some short spike on the sensor output, that could possibly be the reason. 

I have seen that when connecting a 4-20 mA signal generator on the fly,  the input has sometimes detect a high error. 

Is the sensor connected on startup? 

According to the diagram given in the manual, there should have been no issues.  Trying a resistor of any value on the inlet as a shunt didn't seem to do anything, nor does the documentation for the sensor seem to give any details about a shunt resistor.  The sensor we are using is this: IFM Efector PX3111 http://www.ifm.com/products/us/ds/PX3111.htm .  I am aware of the IQAN lockout if it senses an error to require a power cycle, and I tried several times to see if the reaction changed, no difference, so here was the setup we used.  24VDC to high side of the sensor, output from the sensor wired up through an ammeter sensing milliamps to the controller input.  Tried without the ammeter, no difference, tried on the other current input, no difference.  The only thing that brought it into the range of readable was adding a parallel resistor as I mentioned.  I realize this makes it inaccurate, that's why I don't want to do this, it was just a test to see if providing less current would be read in the sensor.  The ammeter in the basic setup was reading almost exactly 4mA and we were getting a high error, same after restarting power to the system.  In the end after looking at this for a few days and trying everything I know how to do, we changed it to a voltage input on the controller and added a 250 ohm pulldown resistor to get it near the 0-5V range.  I would still like to figure out why this is not working as advertised however, so please let me know any other ideas.  We also bought an additional sensor to be sent to the guys at ECD for internal testing.  


After some more testing, we have concluded that the protective function that checks for high-error on the CIN is unnecessarily fast, too fast for some applications. When connecting a sensor on the fly, the CIN protective function may detect this as an over-current. It could perhaps be related to an brief overshoot of the sensor current output, or maybe if a switched sensor output regulator is giving some ripple. 

Anyway, the detection time doesn't have to be as fast as it is now, and for 5.04 we are looking at making an MC4x software update that delays the detection of CIN high-error. 


Version 5.04 is released now; with this version the CIN diagnostics has an added delay that prevents the MC4 from triggering the overaload too fast. 

I have just ran into the same issue. I have 3 different 4-20ma current sensors connected to a MC43 and unable to read any of the sensors. I have tested them with another brand of controller and they function as expected when connected to it. When I connect the sensors to the MC43 the current drops to 1.76MA and does not regulate with pressure as it should (these where just tested and confirmed to work on another controller). The connections are made as per the manual with supply voltage at 24 and signal to desired pin C2 33 in this case. I am using iqan version 6.06

Hard to know without knowing the sensor, but I wonder if the sensors that are still having problems are compatible with the input impedance of the MC4x modules. 


I was making an error. I will delete my comment as i forgot i had posted it. the Module was mounted upside down and for some reason i failed to acknowledge this and was backwards on my C1 and C2 connector in turn resulting an incorrect pinout.