Inputs, Calibration offset calibration, Calibration offset – Watlow Electric Integrated Controller User Manual Rev C EZ-ZONE PM User Manual

Page 58: Calibration

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5 6

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C h a p t e r 9 F e a t u r e s

3. Initiate an autotune. (See Autotuning in this

chapter.)

When autotuning is complete, the PID parameters
should provide good control. As long as the loop is in
the adaptive control mode, TRU-TUNE+

continu-

ously tunes to provide the best possible PID control
for the process.

WARNING! During autotuning, the controller sets the output
to 100 percent and attempts to drive the process variable
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).

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

Calibration

To calibrate an analog input, you will need to provide
two electrical signals or resistance loads near the ex-
tremes of the range that the application is likely to
utilize. See recommended values below:

Sensor Type

Low Source

High Source

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

350.00 Ω

1,000 Ω RTD

500.00 Ω

3,500.00 Ω

Follow these steps for a thermocouple or pro-
cess input:

1. Apply the low source signal to the input you are

calibrating. Measure the signal to ensure it is ac-
curate.

2. Read the value of Electrical Measurement

[`Mu]

(Factory Page, Calibration Menu) for that input.

3. Calculate the offset value by subtracting this val-

ue from the low source signal.

4. Set Electrical Input Offset

[ELi;o] (Factory Page,

Calibration Menu) for this input to the offset val-
ue.

5. Check the Electrical Measurement to see whether

it now matches the signal. If it doesn’t match, ad-
just Electrical Offset again.

6. Apply the high source signal to the input. Mea-

sure the signal to ensure it is accurate.

7. Read the value of Electrical Measurement for

that input.

8. Calculate the gain value by dividing the low

source signal by this value.

9. Set Electrical Slope

[ELi;S] (Factory Page, Cali-

bration Menu) for this input to the calculated
gain value.

10. Check the Electrical Measurement to see wheth-

er it now matches the signal. If it doesn’t match,
adjust Electrical Slope again.

Set Electrical Offset to 0 and Electrical Slope to 1 to
restore factory calibration.

Follow these steps for an RTD input:

1. Measure the low source resistance to ensure it

is accurate. Connect the low source resistance to
the input you are calibrating.