66
Startup and Basic Operation
Notes.
If the resistance of the external circuit in thermocouple simulation is
very low (obvious short circuit), the message “O.LOAD” is displayed
until the load is reasonable.
Check that the instrument under test is set for the same thermo-
couple type as selected in MC5-IS. If the type is not one of the
available types, you should simulate in millivolt mode and convert
from temperature to millivolts manually. More information concern-
ing millivolt generation is in chapter Voltage Generation on page
60.
Wire-wound thermocouple temperature indicators and record-
ers are calibrated with known loop resistance, commonly ten or
twenty ohms. The required resistance of the conductors is usually
marked on the device. When calibrating such a device, tune the
loop resistance to the nominal value with an additional resistor.
Use MC5-IS’ 2-wire resistance measurement to tune the loop resis-
tance of a wire wound device. Short circuit the measuring device
for the time of resistance measurement. The resistance measure-
ment may damage the device, if you do not install the short circuit.
For more information on resistance measurement, see chapter
Resistance Measurement on page 42.
Warning!
If you short circuit the thermocouple simulation output, MC5-
IS tries to maintain the voltage by increasing the output cur-
rent. If you then open the output again, the voltage is first too
high, but returns quickly to the correct level. If this voltage peak
could damage the components of the circuit, make sure that
the circuit can not be shorted or protect the circuit against
overvoltage. For the same reason, always enter 0°C output
before connecting the circuit.
If you connect an RTD sensor to the ET module’s R, RTD con-
nectors, there is no galvanic isolation between the thermo-
couple and the RTD sensor.
Next…
Thermocouple Measurement (Temperature) on page 49
RTD and Resistance Simulation on page 64
Special Generations on page 67
Calibration, see Part D.
Problems with thermovoltage simulation? See Error situations on page 94.
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