PID Loop Setup

 

The PID Loop Setup screen displays Loop 1 and its control parameter - i.e. % Dissociation/Kn, Loop 2 and its parameter – Temperature, and Loop 3 and its parameter – Backpressure.

 

The top two blue arrows move you from one loop to the other.  Below each of the loops is shown the PID parameters as they exist in the Series 9210 at that particular moment.

 

Using the lower up and down arrow keys allows the operator/supervisor to highlight the parameters shown in the lower portion of the screen.  These parameters include proportional band, reset, rate, probe millivolts, process variable, setpoint, percent output, mode, integral preset, cycle time, setpoint change limit, control mode, low limit, high limit, and 0 setpoint stops control.  Some of the parameters are read-only, such as probe millivolts, process variable, and Pct Out (percent control output).  Pressing the Enter key when the parameter is highlighted can change all of the other parameters.  This will display a numeric keypad or a menu of choices that will allow you to change the specific parameter.  Highlight/enter your choice and press the Enter button to make the appropriate selection.

 

Change setpoint overshoot protection

When the “Change Setpoint” is set to any value other than OFF, the PID control operates normally until there is a setpoint change. When a setpoint change occurs, the PID algorithm uses PB only (i.e. it ignores the Reset (I) and Rate (D)) until the % output from the specified loop falls below the value specified. Then it will begin calculating reset and rate and return to normal operation.

 

Example: Change setpoint is set at 80%; Current setpoint is 1500

New setpoint is 1700 - % output rapidly goes to 100%, PID ignores Reset and Rate.

Temperature gets within PB, % Output starts to drop.

When % Output drops below 80%, PID operation returns to normal with Reset and Rate applied.

 

Normally overshoot is caused by a buildup of the Reset error term.  By ignoring this term until the temperature is with PB, the Reset term is minimized, thus reducing the overshoot error. You should be cautious not to set the Change Setpoint value too low - e.g. if the furnace controls 1700 in a steady state at 50% output and you set the Change Setpoint value to 40% and the PB value is low, you could find yourself in a situation where you never see 40% output and remain in a PB only control mode.

 

Default PID Parameters for Loop 1 - %Dissociation/Kn, Loop 2 – Temperature, and Loop 3 - Backpressure

 

Loop 1 Default PID Parameters

Loop 2 Default PID Parameters

Loop 3 Default PID Parameters

Proportional Band: 1.3

Proportional Band: 20.0

Proportional Band: 4.0

Reset:  0.01

Reset:  0.10

Reset:  0.10

Rate: 0.00

Rate: 0.0

Rate: 0.0

Mode: Auto

Mode: Auto

Mode: Auto

Integral Preset: 0

Integral Preset: 0

Integral Preset: 0

Cycle time: 24

Cycle time: 60

Cycle time: 60

Setpoint Change Limit: OFF

Setpoint Chazge Limit: 80%

Setpoint Change Limit: OFF

Control Mode: Dual Direct

Control Mode: Single Reverse

Control Mode: Single Reverse

Low Limit: -100

Low Limit: 0

Low Limit: 0

Hight Limit: 100

Hight Limit: 100

Hight Limit: 100

0 set point stops control: no

0 set point stops control: no

0 set point stops control: no

 

The Esc key on some of the screens returns you to the previous screen without any changes taking affect. From the PID Setup screen, the Esc key takes you back to the Menu screen.