Omega Engineering CL521 Operator's Manual page 30

- Increasing or decreasing the output signal smoothly:
If the measuring device must be made to show some specific steady reading, first enter
the corresponding calibration value from the numeric pad, and then change it using the
Up and Down arrow keys until the measuring device shows the required reading. If the
necessary correction is large, press the arrow key for a longer time. After one second,
the calibration value will begin to change at a progressive rate. Release the key before
the measuring device indication approaches the required value and continue with single
steps if necessary.
Each thermocouple type has been assigned a specific simulation range. If values
outside this range are used, the display will flash the corresponding maximum or
minimum value. If the compensation temperature goes outside the range of -10 to
+70°C, the display will indicate "CJ LO" or CJ HI" correspondingly.
7.2.3 The Effect of Loading
The CL521 thermocouple output is restricted to about 0.6 mA (E = 60 mV). Thus the
stabilization time of the simulation value increases when devices that cause circuit
loading, such as wirewound meter movement devices, are being checked. If the device
contains a short circuit, or if the resistance of the device to be checked is too low,
"OLOAd" is displayed. If reaching the simulation value takes more than about two
seconds, the resistance of the measuring device is so small that the effect of the lead
resistance must also be considered.
Wirewound meter movement devices used in conjunction with thermocouples are
normally calibrated for proper indication when the total lead resistance of the conductors
is known, commonly ten or twenty ohms. The necessary conductor lead resistance is
marked on the indicating device. When checking such devices, an equivalent resistance
must be included in the circuit.
Figure 7-5. Calibrating an Analog Meter with the CL521
When part of the original wiring is included in the circuit that is being checked, the added
resistor must be adjustable. The wire resistance should be set to the required value by
shorting the indicating device and using the TC measurement on the CL521.
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