Curve Selection - Lakeshore 335 User Manual

4.4.7 Curve Selection

It is best practice to use the same material for thermocouple wires; if it is at all possible, it
is also best to avoid splices. When splices are necessary, continue the splice with the same
type of material.
For less demanding applications, a short across the input terminals will suffice. Both
thermocouple inputs should be calibrated on either channel A or B, even if they use
the same type of thermocouple. An appropriate curve must be selected and room
temperature compensation must be turned on before calibration can be started.
Follow this procedure to calibrate room temperature compensation:
For best results, the calibration temperature should be close to the measurement tem-
perature that requires best accuracy.
1. Attach a thermocouple sensor or direct short across the input terminals of the
thermocouple input. See FIGURE 3-7 for polarity.
2. Place the instrument away from drafts. If you are calibrating using a short, place
an accurate room-temperature thermometer near the terminal block.
3. Allow the instrument to warm up for at least 0.5 h without moving or handling
the sensor.
4. If you are calibrating with a short, skip to step 6, otherwise insert the thermocou-
ple into the ice-bath, liquid nitrogen, helium Dewar, or other known, fixed tem-
perature.
5. Read the displayed temperature. If the temperature display is not as expected,
check to be sure that the thermocouple is making good thermal contact. If possi-
ble, add a thermal mass to the end of the thermocouple.
6. Press Input Setup and select the corresponding sensor input. Press Enter until
the Room Calibration parameter appears, then press  until Yes appears; press
Enter to accept it.
7. The current temperature reading is displayed in kelvin. Enter the true tempera-
ture that the thermocouple should read. If the input is shorted, then enter the
actual room temperature measured by the thermometer. Press Enter to save the
value.
8. To verify the calibration, check that the temperature reading for the calibrated
input matches the room temperature calibration setting value.
Any previous calibration can be cleared using the Clear Calibration submenu.
Menu Navigation:
Input SetupQRoom CalibrationQClear Calibration
Default: Room calibration cleared
The Model 335 supports a variety of temperature sensors manufactured by
Lake Shore and other manufacturers. After the appropriate sensor type is selected
(section 2.2), an appropriate curve may be selected. The Model 335 can use curves
from several sources. Standard curves are preloaded with every instrument, and they
are numbered 1 to 20. User curves, numbered 21 to 59, can be used when a sensor
does not match a standard curve. SoftCal™ calibrations are stored as user curves or
the user can enter their own curves from the front panel (section 5.9) or computer
interface (section 6.2). The complete list of sensor curves preloaded in the Model 335
is provided in TABLE 4-8.
During normal operation, only the curves that share the input type you have selected
are displayed. If the curve you wish to select does not appear in the selection
sequence, make sure the curve format matches the recommended format for the
input type selected. Refer to TABLE 4-6.
4.4.7 Curve Selection 51
|
www.lakeshore.com