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Lake Shore Model 325 Temperature Controller User’s Manual
Advanced Operation 5-1
CHAPTER 5
ADVANCED OPERATION
5.0 GENERAL
This chapter provides information on the advanced operation of the Model 325 temperature controller.
5.1 CURVE NUMBERS AND STORAGE
The Model 325 has 20 standard curve locations, numbered 1 through 20. At present, not all locations are occupied by
curves; the others are reserved for future updates. If a standard curve location is in use, the curve can be viewed using the
edit operation. Standard curves cannot be changed by the user, and reserved locations are not available for user curves.
The Model 325 has 15 user curve locations, numbered 21 through 35. Each location can hold from 2 to 200 data pairs
(breakpoints), including a value in sensor units and a corresponding value in kelvin. Using fewer than 200 breakpoints
will not increase the number of available curve locations. SoftCal-generated curves are stored in user curve locations.
5.1.1 Curve Header Parameters
Each curve has parameters that are used for identification and to allow the instrument to use the curve effectively.
The parameters must be set correctly before a curve can be used for temperature conversion or temperature control.
Curve Number: 1
–
35.
Name: Defaults to the name User Curve for front panel entry. When entering a user curve over the computer interface, a
curve name of up to 15 characters can be entered.
Serial Number: Up to a 10-character sensor serial number. Both numbers and letters can be entered over computer
interface; only numbers can be entered from the front panel.
Format: The format parameter tells the instrument what breakpoint data format to expect. Different sensor types require
different formats. Formats for Lake Shore sensors are:
V/K: Volts vs. kelvin for diode sensors.

/K: Resistance vs. kelvin for platinum RTD sensors.
Log

/K: Log resistance vs. kelvin for NTC resistive sensors.
mV/K: Millivolts vs. kelvin for thermocouple sensors.
Limit: Enter a temperature limit in kelvin for the curve. Default is 375 K. Enter a setting of 9999 K if no limit is needed.
Temperature Coefficient: The unit derives the temperature coefficient from the first two breakpoints. The user does not
enter this setting. If it is not correct, check for proper entry of those points. A positive coefficient ( P ) indicates that
the sensor signal increases with increasing temperature. A negative coefficient ( N ) indicates that the sensor signal
decreases with increasing temperature.
5.1.2 Curve Breakpoints
Temperature response data of a calibrated sensor must be reduced to a table of breakpoints before entering it into the
instrument. Each breakpoint consists of one value in sensor units and one temperature value in kelvin. Linear
interpolation is used by the instrument to calculate temperature between breakpoints. From 2 to 200 breakpoints can be
entered as a curve. The instrument will show an error message on the display if the sensor input is outside the range of
the breakpoints. No special endpoints are required. Sensor units are defined by the format setting in Table 5-2.
Breakpoint setting resolution is six digits in temperature. Most temperature values are entered with 0.001 resolution.
Temperature values of 1000 K and greater can be entered to 0.01 resolution. Temperature values below 10 K can be
entered with 0.0001 resolution. Temperature range for curve entry is 1500 K.