332S Lake Shore Cryotronics Temperature Controller

The Lake Shore Cryotronics 332 Series Temperature Controllers incorporate advanced electronics for high resolution temperature measurement and control. The 332 automatically scales excitation current to support Cernox and other negative temperature coefficient (NTC) resistors to as low as 500 mK. The 332 also includes 50 W and 10 W heater outputs for greater flexibility in cryocooler applications requiring a second heater for fine and coarse control.

The 332 temperature controller features two inputs, with a high-resolution 24-bit analog-to-digital converter and separate current source for each input. Sensors are optically isolated from other instrument functions for quiet and repeatable sensor measurements. The two sensor inputs included in the 332 can be configured to measure and control nearly any diode, RTD, and thermocouple temperature sensor. Sensor inputs for both versions of the 332 are preconfigured and compatible with either diode/RTDs or thermocouple sensors. Software selects appropriate excitation current and signal gain levels when sensor type is entered via the instrument front panel. With NTC RTD sensors at temperatures as low as 500 mK, and with resistance being as high as 75 kΩ, the 332 automatically provides an excitation current down to 1 µA. This minimizes sensor self-heating induced errors. At higher temperatures, when resistance is low and concern for sensor self-heating is minimal, the 332 provides an excitation current up to 1 mA for a better signal to noise ratio and high measurement resolution. The 332 also uses current reversal to eliminate thermal electromotive force (EMF) errors for all resistive sensors. Standard temperature response curves for silicon diodes, platinum RTDs, and many thermocouples are included. Up to twenty 200-point CalCurves for Lake Shore calibrated sensors or user curves can be loaded into non-volatile memory via a computer interface or the instrument front panel. A built-in SoftCal algorithm can also be used to generate curves for silicon diodes and platinum RTDs, for storage as user curves.

For the greatest flexibility in temperature control, the 332 has two independent, proportional-integral-derivative (PID) control loops that drive two heater outputs of 50 W and 10 W. 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 manually or the Autotuning feature of the 332 can automate the tuning process. The Loop 1 heater output is a well-regulated variable DC current source. The output is optically isolated from other circuits to reduce interference and ground loops. The 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. The second control loop heater output is a single-range, variable DC voltage source that can vary from 0 V to 10 V. The output can source up to 1 A of current providing a maximum of 10 W of heater power. The setpoint ramp feature allows smooth continuous changes in setpoint and also makes 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 zone value on setpoint change.

The 332 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. Each input has a high and low alarm which offer latching and non-latching operation. The two relays on the 332 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 data acquisition system. The user may select the scale and data to be 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.