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3.8 Calibrating the 4 to 20mA Output
The 4 to 20mA output of the
pro
CHEM
-S
is factory calibrated. However,
TPS has provided calibration controls for the 4mA and 20mA points in
case this requires adjustment in the field.
Calibrating the 4 to 20mA output…
1. Connect a Digital Milliamp Meter between terminals 17 and 18.
2. Switch the
pro
CHEM
-S
to
Set Upper Limit
.
3. Adjust the
Set Upper Limit
control until the display reads 0.00 (for
the standard 4 to 20mA output) or the Salinity/TDS that corresponds
to 4 mA (for a custom 4 to 20 mA output).
4. Adjust the
4-20mA ZERO
(RV1) trimmer in the terminal area until the
Digital Milliamp Meter reads 4 mA.
5. Adjust the
Set Upper Limit
control until the display reads 1000,
regardless of decimal point location (for the standard 4 to 20mA
output) or the Salinity/TDS that corresponds to 20 mA (for a custom
4 to 20 mA output).
6. Adjust the
4-20mA SPAN
(RV3) trimmer in the terminal area until the
Digital Milliamp Meter reads 20 mA.
In the event that the
LIMIT
control does not have sufficient
adjustment to reach 0.00 or 1000, calculate the expected output level
and use this for calibration. Remember that the difference between 0
and 1000 is to be made 16mA.