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Lake Shore Model 325 Temperature Controller User’s Manual
Introduction 1-1
CHAPTER 1
INTRODUCTION
1.0 PRODUCT DESCRIPTION
The Model 325 dual-channel temperature controller is capable of supporting nearly any diode, RTD, or thermocouple
temperature sensor. Two independent PID control loops with heater outputs of 25 W and 2 W are configured to drive
either a 50 Ω or 25 Ω load for optimal cryocooler control flexibility. Designed with ease of use, functionality, and value
in mind, the Model 325 is ideal for general-purpose laboratory and industrial temperature measurement and control
applications.
Sensor Inputs
The Model 325 temperature controller features two inputs with a high-resolution 24-bit analog-to-digital converter and
separate current sources for each input. Constant current excitation allows temperature to be measured and controlled
down to 2.0 K using appropriate Cernox™ RTDs or down to 1.4 K using silicon diodes. Thermocouples allow for
temperature measurement and control above 1,500 K. Sensors are optically isolated from other instrument functions for
quiet and repeatable sensor measurements. The Model 325 also uses current reversal to eliminate thermal EMF errors in
resistance sensors. Sensor data from each input is updated up to ten times per second, with display outputs twice each
second. Standard temperature response curves for silicon diodes, platinum RTDs, ruthenium oxide RTDs, and many
thermocouples are included. Up to fifteen 200-point CalCurves
®
(for Lake Shore calibrated temperature sensors) or user
curves can be stored into non-volatile memory. A built-in SoftCal
®
algorithm can be used to generate curves for silicon
diodes and platinum RTDs for storage as user curves. The Lake Shore curve handler software program allows sensor
curves to be easily loaded and manipulated.
Sensor inputs for the Model 325 are factory configured and compatible with either diodes/RTDs or thermocouple
sensors. Your 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 the sensor type is entered via the instrument front panel.
325_Front.bmp
Figure 1-1. Model 325 Front View