Watlow PM LEGACY™ Limit Controller • 86 • Chapter 8 Features
Calibration
Before performing any calibration procedure, verify that the displayed readings are not within pub-
lished specifications by inputting a known value from a precision source to the analog input. Next,
subtract the displayed value with
the known value and compare this
difference to the published accura-
cy range specification for that type
of input.
Use of the Calibration Offset i.Ca
parameter found in the Operations
Page opEr, Analog Input Menu ai
shifts the readings across the en-
tire displayed range by the offset
value. Use this parameter to com-
pensate for sensor error or sensor
placement error. Typically this val-
ue is set to zero.
Equipment required while performing calibration:
Obtain a precision source for millivolts, volts, milliamperes or resistance depending on the sensor
type to be calibrated. Use copper wire only to connect the precision source to the controller’s input.
Keep leads between the precision source and controller as short as possible to minimize error. In ad-
dition, a precision volt/ohm meter capable of reading values to 4 decimal places or better is recom-
mended. Prior to calibration, connect this volt/ohm meter to the precision source to verify accuracy.
Actual input values do NOT have to be exactly the recommended values, but it IS critical that the ac-
tual value of the signal connected to the controller be accurately known to at least four digits.
Calibration of Analog Inputs:
To calibrate an analog input, you will need to provide a source of two electrical signals or resistance
values near the extremes of the range that the application is likely to utilize. See recommended val-
ues below:
Sensor Type Precision Source Low Precision Source High
thermocouple 0.000 mV 50.000 mV
millivolts 0.000 mV 50.000 mV
volts 0.000V 10.000V
milliamps 0.000 mA 20.000 mA
100 Ω RTD 50.00 Ω 350.0 Ω
1,000 Ω RTD 500.0 Ω 3,500 Ω
thermistor 5 kΩ 50.00 5,000
thermistor 10 kΩ 150.0 10,000
thermistor 20 kΩ 1,800 20,000
thermistor 40 kΩ 1,700 40,000
potentiometer 0.000 1,200
Time
Temperature
Temperature Reading
from Sensor
Actual Process Temperature
Negative Calibration Offset will
compensate for the difference
between the Sensor Reading and
the Actual Temperature
To Next Page
Loading...
