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The reference junction temperature in Register 9 can also be checked while using the
internal reference junction compensation (INT), or whiie measuring the reference
junction temperature with a PtIOO probe (PROBE).
4.4 MEASURING THERMOCOUPLE RESISTANCE
The CL521 can be used to measure the resistance of a thermocouple circuit during
thermocouple temperature measurements. The measurement will yield a correct
resistance regardless of the prevailing thermoelectric potential.
Display the circuit resistance by pressing the TC£2 key while in TC & mV mode.
Return to the normal measurement mode by pressing the TC & mV key.
Figure 4-13. Measuring Thermocoupie Resistance with the CL521
The resistance measurement range is 0 to 400 ohms. Exceeding this range causes the
display to blink the maximum allowed resistance. If the measurement circuit is broken,
the display will indicate "OPEN".
Thermocouple resistance measurements can be used:
- to determine the condition of the measurement connections and to help locate short
circuits.
- to help in adjusting the measurement circuit resistance when meter movement
indication devices are used to measure thermoelectric potential.
- to predict the expected lifespan of a thermocouple by monitoring the change in its
resistance as a function of time, and comparing the measured values to data collected
from previous experiences.
- for various checks when accuracy requirements do not warrant the use of three or four
wire connections, for example to determine the wire order when connecting a three or
four wire probe.
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