How do I adjust the bias and gain on my SCR power control?

Bias & Gain Adjustment

The bias & gain must be properly adjusted so that the SCR power control responds properly to the input signal.  ISE configures and adjusts the SCR power control prior to shipment.  If reconfiguration or further adjustment is required the following procedure can be used.

1) A load must be connected when adjustment is made.  If you do not wish to adjust with your process load you must connect some other load such as light bulbs to the output of the SCR control.

2) With some models a resistor is required across the input terminals for mA control inputs such as 4-20mA.  Do not remove this resistor unless you are changing to voltage input.

3) To make the following adjustment you will need a signal source appropriate for your required input range.  You may also be able to provide the required signals from the temperature control by using its auto/manual (place control in manual mode) or maximum output parameters if available.

4) Some 4-20mA input models cannot be converted to zero based inputs such as 0-10V.  They require 4mA to power their electronics.

5) Bias: Adjusts the SCR control output for the minimal signal input (Off Point).

6) Gain: Adjusts the SCR control output for the maximum signal input (Full On Point)



The following adjustment procedure uses the most common input signal of 4-20mA.  Follow the same procedure with other signal inputs.

1) Connect input signal power source and a load to the SCR control.

2) Connect an analog voltmeter across the load.

3) Adjust the input signal to a value slightly above its desired minimum value.  Example: 4.5mA for 4-20mA.

4) Adjust the Bias adjustment until the output voltage just begins to turn on.

5) Change input signal to the desired minimum amount (4mA for 4-20mA).

6) Confirm that no output voltage is present at load.  If output is not off make a small adjustment to the Bias and return to step 3 to check that a small output is present with a small input in the signal.

7) Adjust the input signal to a value slightly less than the the maximum value.  Example: 19.5 mA for 4-20mA.

8) Adjust the Gain until the output is very close to the maximum possible but not the maximum.

9) Change the input signal to maximum amount (20mA for 4-20mA).

10) Check that the output voltage is now maximum.  If not adjust the gain slightly and check that the output reduces slightly if signal is change to value in step 7.

11) Redo steps 3 through 10 until no further adjustment is required.

12) If properly adjusted you will have a smooth change in the output based on the full range of your input signal.