
Lake Shore Model 325 Temperature Controller User’s Manual
1-2
Introduction
Product Description (Continued)
Temperature Control
The Model 325 temperature controller offers two independent proportional-integral-derivative (PID) control loops.
A PID 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.
A high-resolution digital-to-analog converter generates a smooth control output. The user can set the PID values
or the AutoTuning feature of the Model 325 can automate the tuning process.
Control loop 1 heater output for the Model 325 is a well-regulated variable DC current source. The output can provide up
to 25 W of continuous power to a 50
or 25
heater load, and includes a lower range for systems with less cooling
power. Control loop 2 heater output is a single-range, variable DC voltage source. The output can source up to 0.2 A,
providing 2 W of heater power at the 50
setting or 1 W at the 25
setting. When not being used for temperature
control, the loop 2 heater output can be used as a manually controlled voltage source. The output voltage can vary from
0 to 10 V on the 50
setting, or 0 to 5 V on the 25
setting. Both heater outputs are referenced to chassis ground. The
setpoint ramp feature allows smooth continuous setpoint changes and can also make the approach to setpoint more
predictable. The zone feature can automatically change control parameter values for operation over a large temperature
range. Ten different temperature zones can be loaded into the instrument, which will select the next appropriate value on
setpoint change.
Interface
The Model 325 includes both parallel (IEEE-488) and serial (RS-232C) computer interfaces. In addition to data
gathering, nearly every function of the instrument can be controlled via computer interface. Sensor curves can also be
entered and manipulated through either interface using the Lake Shore curve handler software program.
Loop 1 Heater output
Serial (RS-232C) I/O (DTE)
Line input assembly
Loop 2 Heater output
Sensor input connectors
IEEE-488 interface
Figure 1-2. Model 325 Rear Panel Connections
Содержание 325
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