64
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 MC5P. If the type is not one of the avail-
able types, you should simulate in millivolt mode and convert from
temperature to millivolts manually. More information concerning
millivolt generation is in chapter Voltage Generation on page 58.
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 MC5P’s 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 40.
Warning!
If you short circuit the thermocouple simulation output, MC5P
tries to maintain the voltage by increasing the output current.
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 cir-
cuit can not be shorted or protect the circuit against overvolt-
age. For the same reason, always enter 0°C output before con-
necting 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 47
RTD and Resistance Simulation on page 62
Special Generations on page 65
Calibration, see Part D.
Problems with thermovoltage simulation? See Error situations on page 96.
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