Keithley 2701, Service Manual

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1-16 Performance Verification Model 2701 Service Manual
Verifying temperature
Thermocouple, thermistor, and RTD temperature readings are derived from DC volts and
resistance measurements respectively. For that reason, it is not necessary to independently
verify the accuracy of temperature measurements. As long as the DC volts and resistance
functions meet or exceed specifications, temperature function accuracy is automatically
verified. However, temperature verification procedures are provided below for those who wish
to separately verify temperature accuracy.
Thermocouple temperature
1. Connect the DC voltage calibrator output terminals to the Model 2701 INPUT jacks
using low-thermal shielded connections. (Use 2-wire connections similar to those
shown in
Figure 1-1 .) Be sure the INPUTS switch is in the FRONT position.
2. Configure the Model 2701 for °C units, type J temperature sensor, and 0°C simulated
reference junction as follows:
a. Press SHIFT then SENSOR and note the unit displays the temperature units:
UNITS: C. (If necessary, use the cursor and range keys to select °C units.)
b. Press ENTER. The unit displays the sensor type: SENS: TCOUPLE.
c. Make sure that TCOUPLE is displayed, then press ENTER. The unit then displays
the thermocouple type: TYPE: K.
d. Select a type J temperature sensor, then press ENTER. The unit then displays the
reference junction type: JUNC: SIM.
e. Make certain that the simulated reference junction type is selected, then press
ENTER. The unit then displays the current simulated reference junction
temperature: SIM: 023.
f. Using the cursor and range keys, set the reference junction temperature to 0°C,
then press ENTER twice to complete the temperature configuration process.
3. Select the temperature function by pressing the TEMP key.
4. Source each of the voltages summarized in Table 1-7 and verify that the temperature
readings are within limits. Be sure to select the appropriate thermocouple type for each
group of readings. (See step 2 above.)
Table 1-7
Thermocouple temperature verification reading limits
Thermocouple type Applied DC voltage* Reading limits (1 year, 18°C to 28°C)
J
K
-7.659mV
0mV
42.280mV
-5.730mV
0mV
54.138mV
-190.2° to -189.8°C
-0.2° to +0.2°C
749.8° to 750.2°C
-190.2° to -189.8°C
-0.2° to +0.2°C
1349.8° to 1350.2°C
* Voltages shown are based on ITS-90 standard using 0°C reference junction temperature. See text for pro-
cedure to set reference junction temperature.