Manual Setting Of Pid Control Parameters; Proportional (P); Integral (I); Derivative (D) - Lakeshore 340 User Manual

6.6

MANUAL SETTING OF PID CONTROL PARAMETERS

This section describes entry of PID control parameters into the Model 340. To select Manual PID control
mode, refer to Paragraph 6.5.
6.6.1

Proportional (P)

The proportional parameter (also called gain) is the P part of the PID control equation. It has a range of 0 to
1000 with a resolution of 0.1. Enter a value greater than zero for P to use closed loop control.
To enter a value for P, press Loop 1 or Loop 2 to display control parameters for that loop in the lower portion
of the display. Press P to highlight the setting field for the P . Enter a value with the number keys and press
Enter to save the change or Escape to return to the previous value. Default is 50.
6.6.2

Integral (I)

The integral parameter (also called reset) is the I part of the PID control equation. It has a range of 0 to 1000
with a resolution of 0.1. Setting I to zero turns the reset function off. The I setting is related to seconds by:
To enter a value for I, press Loop 1 or Loop 2 to display control parameters for that loop in the lower portion
of the display. Press I to highlight the setting field for the I parameter. Enter a value with the number keys and
press Enter to save the change or Escape to return to the previous value. Default is 20.
6.6.3

Derivative (D)

The derivative parameter (sometimes called rate) is the D part of the PID control equation. The range of the D
setting is 0 to 1000 seconds with a resolution of 1 second. Setting D to zero turns the derivative function off.
To enter a value for D, indicate the desired control loop by pressing the Loop 1 or Loop 2 key. The control
parameters for that loop appear in the lower portion of the display. Press the D key and the setting field for the
D parameter is highlighted. Use the number keys to enter a value and press the Enter key to save the change
or the Escape key to return to the previous setting. The default setting is 0.
6.6.4

Manual Output

Manual output is a manual setting of control output. It can function in two different ways depending on control
mode. In open loop control mode, the manual output is the only output to the load. The user can directly set
control output from the front panel or over computer interface as described in Paragraph 9.3. In Manual PID
control mode, the manual output is added directly to the output of the PID control equation. In effect, the
control equation operates about the manual output setting.
Manual output setting is in percent of full scale. When using the heater on Loop 1, percent of full scale is
defined as current or power on the selected heater range. Manual Output setting range is –100% to +100%
with a resolution of 0.01%. Negative values are not recommended with unipolar control outputs.
To enter a manual output value, indicate the desired control loop by pressing the Loop 1 or Loop 2 key. The
control parameters for that loop appears in the lower portion of the display. Press the Manual Output key and
the setting field for the manual output parameter is highlighted. Use the number keys to enter a value and
press Enter to save the change or Escape to return to the previous setting. Default setting is 0.
6.7

SELECTING AN AUTOTUNE CONTROL MODE

The Model 340 AutoTune feature automates the tuning process of typical cryogenic systems. Refer to
Paragraph 2.8 for additional information about the AutoTune algorithm.
Before initiating AutoTune, setup the cooling system with control sensor and heater capable of closed loop
control. Be sure to assign the control sensor with a valid temperature response curve. Assign an appropriate
heater range as described in Paragraph 2.7.1. To speed up the AutoTune process, experiment with Manual
PID tuning to choose good initial control parameters. If no initial parameters are known, start with the default
values of P = 50 and I = 20. It is better to set an initial P value that causes the system to be more active than
desired. Starting with a low P value can increase the time and number of attempts required to tune.
6-4
Lake Shore Model 340 Temperature Controller User's Manual
I
setting
1000
=
I
sec onds
Temperature Control Operation