Lake Shore Model 340 Temperature Controller User’s Manual
Options and Accessories
10-9
10.4.3.2 Measurement Point Connection
Thermocouples are commonly used in high-temperature applications. Cryogenic use of thermocouples offers
some unique challenges. Refer to Paragraph 2.3 for general installation guidelines. Consider the following
when using thermocouples at low temperatures:
• Thermocouple wire is generally more thermally conductive than other sensor lead wire. Smaller gauge wire
and more heat sinking may be needed to prevent leads from heating the sample.
• Attaching lead wires and passing through vacuum tight connectors are often necessary in cryogenic
systems. Remember, the thermocouple wire
is
the sensor; any time it joins or contacts other metal, there is
potential for error.
• Temperature verification and calibration of room temperature compensation is difficult after the sensor is
installed. When possible, keep a piece of the same wire installed in a system for future use.
10.4.3.3 Grounding and Shielding
For lowest measurement noise, do not ground thermocouple sensors. The instrument usually operates with
more noise if one of the thermocouples is grounded. Grounding both thermocouples is not recommended.
The instrument does not offer a shield connection on the terminal block. Twisting the thermocouple wires
helps reject noise. If shielding is necessary, extend the shield from the oven or cryostat to cover the
thermocouple wire, but do not attach the shield to the instrument.
10.4.4 Operation
10.4.4.1 Default
Settings
Following the installation, the 3464 option adds 2 new inputs to the standard front panel operations. This
allows configuration of inputs C and D assigned as thermocouple inputs.
When the instrument is first powered on the default settings for channels C and D are range is ±50 mV range,
temperature compensation is turned ON, and curve 0 (NO CURVE) is selected. If the option card is replacing
another option card all configuration parameter are set to defaults.
10.4.4.2 Input
Selection
After installation, the 3464 option adds 2 new inputs to standard front panel operations, which allows
configuration of inputs
C
and
D
assigned as thermocouple inputs. For example, press
Input Setup
to display
the INPUT SETUP screen. The
s
or
t
key to cycle through inputs
A
,
B
,
C
, or
D
. If
C
or
D
is selected, press
Enter
to display available settings for that thermocouple.
With no option present, only
A
and
B
inputs are available.
10.4.4.3 Displaying Option Readings
Readings from option inputs
C
and
D
can be always be displayed in sensor units, millivolts. If a temperature
response curve is selected for an input, its readings can also be displayed in temperature.
To add an input reading to the display, press the Display Format key.