Voltage And Current Transducers - Quest Controls TELSEC MP2x User Manual

6.2 Voltage and Current Transducers

Connect the voltage or current transducer to the MP2x and then define the Modbus point in the MP2
using the Modbus register map for "Input values as counts from the adc output. See the notes section
where the number of counts vary based upon the type of transducer and load resistor (for mA sensors)
used. Example: defining a humidity sensor that reads 0-100% over 4-20mA output using a 249-ohm load
resistor. The register map shows to use a multiplier of 163 per mA when using a 249-ohm resistor. The
input reading would then be from 652 counts at 0%RH (4mA) and 3,260 counts at 100%RH (20mA). The
range would be 2608 counts (3,260-652) over 0-100% which would be a multiplier of 0.038
(100%RH/2608 counts). The last step would be to add an offset since the range starts at 4mA instead of
0mA. The MP2 applies the offset after the multiplier so the offset would be in the desired engineering
units of %RH which in this case would be -25. The definition using input 20 on the MP2x would be as
follows:
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Rev 2.1 10/21/21 - 13 - TELSEC MP2X User Guide