Lake Shore Model 340 Temperature Controller User’s Manual
10-10
Options and Accessories
10.4.4.4 Curve
Selection
To read temperature from the 3464 option, select a temperature curve for the Model 340. If no curve is
selected, the Model 340 reads in sensor units (millivolts), and if the display is configured to show temperature
for that channel a NO CURVE message displays for that channel. To select a temperature response curve,
press
Input Setup
.
There are 5 standard thermocouple curves included in the Model 340. The user may enter curves of any
thermocouple type. Only curves in mV/K data format display during curve selection. Refer to Appendix A for
lists of data points in each curve.
Table 10-2. Standard Thermocouple Curves
Curve Number
Type
±25 mV Range*
±50 mV Range*
6
K
3.15 K to 864 K
3.15 K to 1500 K
7
E
3.15 K to 622 K
3.15 K to 930 K
8
T
3.15 K to 670 K
3.15 K to 670 K
9
Chromel-AuFe 0.03%
3.50 K to 500 K
3.50 K to 500 K
10
Chromel-AuFe 0.07%
3.15 K to 610 K
3.15 K to 610 K
*
Temperature ranges are without temperature compensation.
10.4.4.5 Curve
Data
Format
Users may enter temperature response curves for all types of thermocouples. Enter curve data in mV/K
format with thermocouple voltage in millivolts and temperature in Kelvin.
The curve must be normalized to 0 mV at 273.15 K (0
°
C). Thermocouple voltages in millivolts are positive
when temperature is above that point and negative when temperature is below that point.
To convert curves published in Celsius to Kelvin, add 273.15 to the temperature in Celsius.
The temperature range for some thermocouple types may extend below 1 K or above 1000 K. The input
voltage of the 3464 is limited to ±50 mV, so any part of the curve that extends beyond ±50 mK is not usable
by the instrument.
A message of S-OVER or S-UNDER on the display indicates that the input is over or under the ±50 mV
range.
10.4.4.6 Range
Selection
The 3464 option inputs have two input voltage ranges: ±25 mV and ±50 mV. Range selection depends on the
Thermocouple type and expected operating temperature. ±25 mV is recommended for cryogenic applications
or higher temperatures that produce less than 500 K. For temperatures above 500 K, the ±50 mV range is
recommended because thermocouple voltage can exceed 25 mV on some thermocouple types. Select the
range that matches the operating temperature.
The thermocouple temperature response curve can help when choosing an input range. Room temperature
compensation can limit the useable range. The voltage range for inputs C and D is set independently. To
select an input range, press
Input Type
.
10.4.4.7 Room Temperature Compensation
Room temperature compensation must be used to correct for the voltage difference between temperature
response curves normalized to 273.15K and instrument operating temperature, room temperature. An
external ice bath is the most accurate form of compensation, but is often inconvenient. The 3464 has built-in
room temperature compensation that is adequate for most applications. The built-in compensation can be
turned on or off by the user. It will operate with any thermocouple type that has an appropriate temperature
response curve loaded. Calibration of the built-in compensation is recommended when a thermocouple is first
installed or any time a thermocouple is changed.