Lake Shore Model 331 Temperature Controller User’s Manual
Product Description (Continued)
Sensor inputs for both versions of the Model 331 are factory configured and compatible with either
diode/RTDs or thermocouple sensors. The purchaser’s choice of two diode/RTD inputs, one diode/RTD
input and one thermocouple input, or two thermocouple inputs must be specified at time of order and
cannot be reconfigured in the field. Software selects appropriate excitation current and signal gain
levels when sensor type is entered via the instrument front panel.
Temperature Control
The Model 331E offers one and the Model 331S offers two proportional-integral-derivative (PID) control
loops. A PID control algorithm calculates control output based on temperature setpoint and feedback
from the control sensor. Wide tuning parameters accommodate most cryogenic cooling systems and
many small high-temperature ovens. Control output is generated by a high-resolution digital-to-analog
converter for smooth continuous control. The user can set the PID values or the Autotuning feature of
the Model 331 can automate the tuning process.
Heater output for Model 331S and Model 331E is a well-regulated variable DC current source. Heater
output is optically isolated from other circuits to reduce interference and ground loops. Heater output
can provide up to 50 W of continuous power to a resistive heater load, and includes two lower ranges
for systems with less cooling power. Heater output is short-circuit protected to prevent instrument
damage if the heater load is accidentally shorted.
The setpoint ramp feature allows smooth continuous changes in setpoint and can also make the
approach to a setpoint temperature more predictable. The zone feature can automatically change
control parameter values for operation over a large temperature range. Values for ten different
temperature zones can be loaded into the instrument, which will select the next appropriate value on
setpoint change.
Interface
The Model 331 is available with both parallel (IEEE-488, 331S only) and serial (RS-232C) computer
interfaces. In addition to data gathering, nearly every function of the instrument can be controlled via
computer interface. Also included is a Model 330 command emulation mode that makes the Model 331
interchangeable with the older Model 330 in software controlled systems.
Each input has a high and low alarm which offer latching and non-latching operation. The two relays on
the Model 331S can be used in conjunction with the alarms to alert the operator of a fault condition or
perform simple on-off control. Relays can be assigned independently to any alarm or be operated
manually.
When not being used for temperature control, the loop 2 control output can be used as an analog
voltage output. It can be configured to send a voltage proportional to temperature to a strip-chart
recorder or data acquisition system. The user may select the scale and data sent to the output,
including temperature, sensor units, or linear equation results. Under manual control, the analog
voltage output can also serve as a voltage source for other applications.
Interface Features of Model 331S and Model 331E
Feature 331S
331E
Numeric keypad
Front panel curve entry
Alarms
RS-232C interface
IEEE-488 interface
Second control loop
Analog voltage output
Two relays
1-2
Introduction
