Watlow EZ-ZONE
®
PM Integrated Controller
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125
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Chapter 9 Features
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WARNING! During autotuning, the controller sets the output to 100 percent and attempts to drive the Process Value toward
the set point . Enter a set point and heat and cool power limits that are within the safe operating limits of your system .
Inputs
Calibration Offset
Calibration offset allows a device to compensate for an inaccurate sensor, lead resistance or other factors that
affect the input value. A positive offset increases the input value, and a negative offset decreases the input
value.
The input offset value can be viewed or changed with Calibration Offset
[`i;CA]
(Operations Page, Analog
Input Menu).
Calibration
Before performing any calibration procedure, verify that the displayed readings are not within published
specifications by inputting a known value from a
precision source to the analog input. Next, sub-
tract the displayed value with the known value
and compare this difference to the published ac-
curacy range specification for that type of input.
Use of the Calibration Offset
[`i ;CA]
param-
eter found in the Operations Page
[oPEr]
, Ana-
log Input Menu
[``Ai]
shifts the readings across
the entire displayed range by the offset value.
Use this parameter to compensate for sensor er-
ror or sensor placement error. Typically this val-
ue is set to zero.
Equipment required while performing cali-
bration:
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 con-
troller’s input. Keep leads between the precision source and controller as short as possible to minimize error.
In addition, a precision volt/ohm meter capable of reading values to 4 decimal places or better is recommend-
ed. 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 actual
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 values 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