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PWM Output Commanded to 0, but voltage measured at Output

BFSENGR 1 month ago in Master modules / MC4x • updated by Gustav Widén (System support) 4 weeks ago • 3

IQAN Tech Support,

We are looking for help with troubleshooting our "IQAN Controller, Master Unit, IQAN - MC43" Safety Controller. It is getting inputs from two Temposonics tank-level sensors in our electronic water-level system, models GB Series & RF 5th Gen input sensors. The IQAN controller is PN 20085113.

We are receiving a potential difference (voltage output) of 0.39 V from Output pin to System Ground when measured with a multimeter; however the programming software indicates that the output should be 0 V. Our known inputs and outputs are below:

Inputs

Outputs

I!: Inclinometer 

    Connector 1, Pin 26

    0 – 5 V

    O1: High

      Connector 1, Pin 48

      0.24 V (Pin-to-Pin)

      I2: AFT Level Sensor

        Connector 1, Pin 53

        4 - 20mA

        O2: Low

          System Ground

          I3: FWD Level Sensor

            Connector 2, Pin 33

            4 - 20mA

            ***SHOULD BE = 0.0 V Output***
              • The tank level sensors are bottomed-out, as there is no water in the tank.
              • With no water in the tank, the IQAN is programmed to output 0% Du Cycle, yielding 0.0 gallons on the display - but there is a .39V measured.
              • The lowest water level reading that the sensors could output is 120 gallons, but should read 0.0 gallons below that.
              • We are needing help troubleshooting and establishing / calibrating our 0.0 baseline

              Questions: 

              1. Why is a voltage being read at the output, when the program is indicating that it should be zero? 

              2. Can we create a code or loop in the program to circumvent the small output voltage?

              Gustav Widén (System support) 4 weeks ago

              On the PWM out HS, the voltage you measure on the pin when the output is off depend on the leakage current, module supply volage and the connected load.

              Image 4755

              All highside switches have a leakage current. The relatively high leakage current on this output is from an internal pull-up resistor used for open load detection on connected coils. 

              BFSENGR 4 weeks ago

              Thank you for the insight, Gustav! 


              Is it concerning that our output reading is 100 X of the expected leakage? Please realign me if needed - but, rough metal math tells me, (depending on resistance), 2mA x 100 = 0.2V, correct?  [0.002V = 2mA,, and our output is 0.24V which is 100X]. 

              Gustav Widén (System support) 4 weeks ago

              Is your connected load 100 ohm?

              Then 2 mA*100 Ohm = 0.2 V measured between output pin and load when the HS switch is off seems about right, and in the same ballpark as the 0.24 V you measured. 

              Customer support service by UserEcho