Rosemount Model 444 Alphaline Temperature Transmitters
3-8
FIGURE 3-5. Ice Bath
Calibration Diagram.
CALIBRATING A
LOW-POWERTRANSMITTER
Calibration Equipment Required
Volt met er. Such as a 5-digit DVM. Accuracy is ±0.01%; resolution is 1 mV.
dc Power Supply. Power capability is 5 V dc at 1.5 mA for Model 444LL and 8 V
dc at 2 mA for Model 444LM.
Resistance Decade Box. Precision type, 5-dial, with largest dial providing 100-
ohm steps. Accuracy is ±0.02 ohm. The decade box should be periodically
calibrated against a 5-dial Wheatstone bridge.
Lead Simulation Resistors. If the transmitter is to be mounted remote from the
RTD, and the lead resistance between the transmitter and the RTD is greater
than 2 ohms per lead (equivalent to 200 ft of 20 AWG wire), the transmitter
should be trimmed with simulated lead resistances for best accuracy. This
requires wirewound resistors with resistance values equal to the nominal lead
resistance of the RTD.
Load Resistor. If the transmitter is to be operated with a load that is
significantly different from the DVM used for calibration, a load resistor can be
used for best calibration accuracy. A metal film, carbon comp, or wirewound
resistor, as well as a decade box can be used to simulate the actual load.
444-0217A
DVM
DVM
Power
Supply
(Alternate Readout)
Thermocouple
Wire
Input
Monitor
DVM
Millivolt
Source
Ice Bath
+
–
+
–+–
+
–
–
+
+
–