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Troubleshooting analog inputs

Issue

An analog input reads the wrong value. Is it the controller or the sensor?

Environment

Analog inputs on I/NET controllers

Cause

Determining where the problem originates - a failed sensor or a bad input - will help arrive at a solution faster.

Resolution

  1. Open the conversion coefficient calculator
  2. Set the high and low values for counts and units to configure the input to show raw voltage input.  Let it enter that result into an open entry in the CC table.
    • On a 7716/7718/7728 or 7756 upper board: Enter 0 for counts low and 4095 for counts high, 0 for units low and 5 for units high
    • On the lower board of the 7756: Enter 0 for counts low and 65535 for counts high, 0 for units low and 10 for units high. 
    • On an MR-88 or 632: Enter 0 for counts low and 255 for counts high
    • On an MR-55 or an ASC: Enter 0 for counts low and 255 for counts high, units low 1.5 and units high 4.
    • If this is a DPU, DIO or DIU, this does not apply to this situation.
  3. Select that conversion coefficient for the input in question and make sure there is no look up table for it. The input will now show the measured voltage for that input.
  4. Read that voltage on the actual input with a meter and compare to the reading on the screen, viewcon or HHC.
    1. If the readings match, the problem is the sensor, your conversion coefficient, or your look up table.
    2. If not, the problem is in the controller. Refer to other articles about possible configuration problems on inputs.
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