Lake Shore Model 321 Autotuning Temperature Controller User’s Manual
1-2
Introduction
1.1 DESCRIPTION
The Model 321 is a microcontroller-based autotuning temperature controller which provides a simple,
low-cost answer to basic control needs. There are three models: the 321-01 for Silicon Diode
Temperature Sensors, the 321-02 for Platinum Resistors, and the 321-04 for Thermocouples.
The controller displays the temperature in K, °C or sensor units in volts (V), millivolts (mV), or ohms (
Ω
).
The 2 x 16 LCD simultaneously displays temperature, setpoint, heater range, and heater % current.
Precision thermometry is the most basic building block of any digital controller and is necessary for
stable, accurate control. Careful analog design provides the Model 321 with stable and repeatable
measurements. A differential input allows for a four-lead measurement of the sensor signal. A high
resolution A/D converter digitizes the signal for use in thermometry, control, and autotuning.
The control software in the Model 321 compares the measured value of the control sensor to the
desired control setpoint and acts with three term (PID) function to minimize the difference. Control
parameters can be entered in any one of five tuning modes: Autotuning P, Autotuning PI, Autotuning
PID, Manual, and Zone.
Autotuning represents the Lake Shore commitment to bringing convenience and performance to the
cryogenic measurement and control market. Autotuning utilizes information gathered during setpoint
changes to automatically optimize the control parameters.
The Model 321 allows the user to program up to 10 custom temperature zones where the controller will
automatically use pre-programmed PID settings and heater range.
The ramping feature permits the user to set the rate that the setpoint increases or decreases when the
setpoint is changed. If this feature is combined with the zone feature, the user could do a ramp through
all 10 zones from
≈
2 K to room temperature by only changing the setpoint. The controller will change
the PID and heater range settings as the temperature setpoint passes through the different zones.
Two heater ranges, with the high providing 25 watts and the low 2.5 watts, accommodate a variety of
cryogenic cooling systems. The power output of the Model 321 is a quiet, variable DC current to ensure
as little noise coupling as possible between the heater and experiment.
The Serial Interface provides remote access to data from the Model 321 and allows setting of most front
panel functions. The Serial Interface is fully compatible with the older Model 320 (with the exception of
the added heater range), minimizing the need for reprogramming.
Model 321 thermometry accuracy can be enhanced by using a Lake Shore calibrated sensor and 8000
Series Precision Calibration Option, or by the use of SoftCal™.
P-321-1-1.bmp
Figure 1-1. Model 321 Temperature Controller Front Panel
