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+®continuously tunes to provide the best possible PID control for the process.

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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).

Follow these steps for a thermocouple or process 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:

Temperature Reading from Sensor

Temperature

Actual Process Temperature

Negative Calibration Offset will compensate for the difference between the Sensor Reading and the Actual Temperature

1. Measure the low source resistance to ensure it

is accurate. Connect the low source resistance to

the input you are calibrating.

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 resistance.

4. Set Electrical Input Offset [ELi;o] (Factory Page,

Calibration Menu) for this input to the offset val-

ue.

Time

Calibration

To calibrate an analog input, you will need to provide two electrical signals or resistance loads near the extremes 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

 

 

 

5. Check the Electrical Measurement to see whether

it now matches the resistance. If it doesn’t match,

adjust Electrical Offset again.

6. Measure the high source resistance to ensure it

is accurate. Connect the high source resistance to

the input.

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.

Watlow EZ-ZONE®PM Integrated Controller

• 56 •

Chapter 9 Features