Table of Contents
Advertisement
Lake Shore Model 330 Autotuning Temperature Controller User's Manual
3.3.2.1
Voltage Resolution (Models 330-1X, -3X, and -4X Only)
Use voltage mode for diode input. In voltage mode, the display resolution is 0.0001 Volt (V) below 2 volts. For
thermocouple input, the display is in millivolts. The millivolt display resolution is 1 microvolt.
3.3.2.2
Resistance Resolution (Model 330-2X Only)
Resistance mode is allowed for the Platinum Resistor input configuration. The display resolution, in resistance,
is 0.01 Ω below 200 Ω and 0.1 Ω above 200 Ω.
3.3.3
Ramp
The ramping feature allows the user to set the rate at which
the temperature setpoint increases or decreases when the
user changes the setpoint. The ramp rate range is from 0.1
to 99.9 degrees per minute. Ramp only works if the
controller reads in temperature units (K or °C). Setting to 0
turns the ramp function off.
For example, to change the setpoint from 50 K to 100 K at a
rate of 1 k/min, press and hold the Set Point key. The
display to the right appears. Use the numeric keypad to
enter the ramp rate of 1.0. Press Enter to accept the new
ramp rate and display the normal display. Press Setpoint
and use the numeric keypad to enter 100 K.
The display slowly changes to 100 K at a rate of 1 K per minute, reaching 100 K in 50 minutes. To stop the
ramp at any point, press Setpoint followed by Enter.
3.3.4
Autotune
There are three Model 330 automatic tuning modes: Auto P, Auto PI, and Auto PID. The Autotuning algorithm
determines proper settings for Gain (Proportional), Reset (Integral) and Rate (Derivative) by observing system
time response upon changes in setpoint under either P, PI or PID control.
Adaptation of an Autotuning algorithm for use at cryogenic temperatures is more complex than for more
stable, predictable, high-temperature loads. For example, over its useful temperature range, a single
cryogenic load may exhibit thermal property variations of three orders of magnitude or greater.
A temperature setpoint change initiates the Autotuning function. When Autotuning is active, the TUNE light
blinks, and the controller automatically gathers data to determine optimum control parameters. The TUNE light
stops blinking and tunes no more until the next setpoint change. The controller never disturbs the system. It
tunes only on user setpoint changes.
System design is also a factor. Under some circumstances, very fast cryogenic systems may not provide
sufficient data points on step changes to accurately predict proper control settings. Unusually large thermal
lags, caused by poor placement and mounting relative to the heater, can obstruct the correlation between the
heater and the system necessary to tune properly.
For slower systems with longer time constants, which are very difficult to tune manually, Autotuning can obtain
enough information on a step change to characterize the system and determine proper values for Gain, Reset,
and Rate.
To put the controller in Autotune PID mode, hold the Autotune key and press the t key to cycle the Control
window display to P, PI, or PID. Release when the desired setting is reached. The "TUNE" annunciator in the
upper Sample window comes on when any of the selected Autotuning elements is active. Note that Autotuning
is for PID settings only. Autotuning does not set or change the heater range; the user must select the proper
heater range for their system. NOTE: The Model 330 only controls when set to temperature units.
Operation
Sample
Control
3-9
Hide quick links:
Advertisement
Table of Contents
