Lake Shore Model 340 Temperature Controller User’s Manual
Options and Accessories
10-11
To turn room temperature compensation on or off, press
Input Setup
. The input setup setting screen appears
with the input letter in the top left hand corner. Use the
s
or
t
key to select an input. Press
Enter
to display
parameters for that input. Press
Next Setting
until the room compensation (
Room Comp:
) field highlights,
then use the
s
or
t
key to select on or off. Press
Save Screen
to store the changes in the Model 340. The
default setting is On.
Room Temperature Calibration Procedure
Field calibration of room temperature compensation is important. Factory calibration is accurate to within
±1 K. Differences in thermocouple wire and installation technique account for most of that error.
Achieve the best accuracy by calibrating the thermocouple used. If that is not possible, use a thermocouple
made from the same wire. For less demanding applications, a short across the input terminals will work.
Calibrate both inputs even if they use the same type of thermocouple.
1. Attach thermocouple sensor or direct short across input terminals of input
C
or
D.
Refer to
Table 10-1 for polarity.
2. Place the instrument away from drafts with an accurate room temperature thermometer near the
thermocouple or terminal block.
3. Allow the instrument to warm up for at least one half hour without moving it or handling the sensor.
4. Insert the Thermocouple into the ice-bath, liquid nitrogen, or helium dewar. This temperature should be
close to the measurement temperature. The further away the operating temperature is from the Room
Compensation temperature the greater the chance of error.
5. Read the displayed temperature. Standard laboratory practices are expected, the temperature at the top
of a dewar of liquid nitrogen is different from the bottom. If the temperature display is not as expected,
check where the Thermocouple is contacting the liquid. Or possibly, add a thermal mass to the end of the
Thermocouple that is being dipped.
6. Press
Input Type
, select input
C
or
D
, and press
Enter
. Press
Next Setting
until the
Room Comp
field
highlights, then press
Enter
. Use the
s
or
t
key to select EXECUTE, and press
Enter.
7. A pop up menu appears with the currently read temperature displayed. Enter the true temperature that
the Thermocouple should read. If inputs are shorted, then enter the actual room temperature measured
by a thermometer device.
8. Press
Save Screen
to complete the calibration for that input.
9. The Model 340 turns internal room temperature compensation ON when calibration completes. To verify
calibration, check that the temperature reading for the calibrated input matches the room temperature
calibration setting value.
10.4.5 Computer Interface Commands
Most of the computer interface commands used by the Model 340 are independent of installed options or
sensor type. The following commands or formats change when the 3464 is installed.
1. In command strings the <input> field accepts
A
,
B
,
C
, or
D
instead of only
A
and
B
.
2. Sensor units for inputs
C
and
D
are millivolts(mV).
3. The INSET command changes to the following format. The INSET? query changes accordingly.
INSET <input>,[<enable>],[<compensation>]
<input>:
Specifies input to configure: (
C
or
D
).
<enable>:
Specifies whether input is allowed to read.
<compensation>:
Room temperature compensation
not
thermal EMF compensation.
4. The INTYPE command changes to the following format. The TYPE? query changes accordingly.
INTYPE <input>,,,,,<range>
<input>:
Specifies input to configure: (
C
or
D
).
<range>:
Specifies input voltage range:
1
= 25mV,
2
= 50mV.