AIG (Customer) asked a question.

July 29, 2026 at 8:45 AM
So, I have the productivity 2000 series PLC. At 4mA, the expected engineering value should be less than or equal to 13107 but each channel of the analog modules gave different values above 13107 as I can see pressure readings on the HMI at no pressure.

So, I have the productivity 2000 series PLC. Recently, I noticed that even without flow or pressure in the system, there were value showing on the HMI. So I felt the drift might be as a result of calibration and after calibrating the pressure transmitter, at 4mA the engineering value is still above 13107. without the PLC, using a multimeter, the measured current is steady 4mA. Same applies when the multimeter was in series with the PLC. I got 4mA on the meter but 13140 in the PLC instead of less than 13107. Please has anyone experienced this issue before?

  • 5 answers
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  • AIG (Customer)

    Hi,

     

    I have eliminated the issue to be the PLC as using a 4-20mA generator gives 4mA at 4mA. I have also used an external power supply, isolated the transmitter from the PLC and using a multimeter, its reading 4.03mA which confirms that the issue is not the PLC. I got the same value when I used an external power supply so I do not think its the control panel power supply as well. Its just strange that all the transmitters are reading above 4mA without any pressure in the system.

     

    Thanks for your support. Its well appreciated.

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  • ADC Community_02 (Automationdirect.com)

    A couple of things line up with what you're seeing:

     

    The P2-08AD-1 is a 16-bit module with a native 0–20mA input range, so at 4mA the expected raw count is 13107 (4/20 × 65535). Your calculation is correct.

     

    The module's published accuracy spec allows for a maximum inaccuracy of 0.1% of range (including temperature drift), which works out to roughly ±65 counts. The 33-count offset you're seeing (13140 vs. 13107) is within that tolerance — so this isn't necessarily a defective module, though I understand it's frustrating when you're expecting a clean value at a known input.

     

    Since it's showing up on the raw count itself (not the scaled engineering value), a couple of quick checks would help pin down whether this is just normal tolerance or something worth pursuing further:

     

    Try the same 4mA source on a different channel on this module. If other channels read closer to 13107, the offset may be isolated to that one channel. If they all read similarly high, it's more likely an overall module calibration sitting near the edge of its tolerance band.

     

    Check ambient temperature at the module — the drift spec is ±25 ppm/°C, so this matters more in hot panels.

     

    Has this channel always read slightly high, or did it start recently?

     

    If it's isolated to one channel, I'd recommend reaching out to AutomationDirect tech support with your readings — that could indicate a channel-specific hardware issue and may be worth an RMA. If it's consistent across channels and within spec, you have the option of just applying a small offset correction in your scaling in Productivity Suite rather than replacing the module.

     

    Let us know what you find on the other channels — that'll point us in the right direction.

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    • AIG (Customer)

      Hi,

       

      Many thanks for your response

       

      I have swapped to another channel and its the same observation- high values

       

      Between the time I made the first post and now, the raw count has increased to 13220 and 4.03mA on the meter for the referenced channel. other instrument on other channels on the same card are also high and increased over time while under the same condition of no pressure in the system.

       

      there are 3 analog card (P2-8AD4DA-1) and all channels in use are high at no flow or pressure.

       

      One observation this morning was that when I swapped the CPU to another, all the values were below 13107 as expected for some minutes. However, 1 or 2 channels started to creep up and few minutes later other channels on card and others moved up as well and kept on increasing as time went by.

       

      we have been using this PLC for over 2 years, this is the fist time we are experiencing this.

       

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      • ADC Community_02 (Automationdirect.com)

        We haven't had any reports from other customers experiencing this issue. Do you happen to have a current calibrator that you can put on a single channel of the module to see if the issue still persists? That removes the any possible noise or interference from your system.

         

        How is your grounding? Any possible ground loops?

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      • ADC Community_02 (Automationdirect.com)

        Have you checked the external 24VDC supply voltage itself during the climb — does it stay rock steady, or does it sag/drift over the same timeframe?

  • AIG (Customer)

    Hi,

     

    I have eliminated the issue to be the PLC as using a 4-20mA generator gives 4mA at 4mA. I have also used an external power supply, isolated the transmitter from the PLC and using a multimeter, its reading 4.03mA which confirms that the issue is not the PLC. I got the same value when I used an external power supply so I do not think its the control panel power supply as well. Its just strange that all the transmitters are reading above 4mA without any pressure in the system.

     

    Thanks for your support. Its well appreciated.

    Expand Post
    Selected as Best

 

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