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3-9
Calibration
Calibration Procedure The following steps describe the procedure for calibrating a low-power
transmitter, as shown in Figure 3-6:
1. Remove the cover from the terminal side of the transmitter housing.
2. If an RTD is already connected, remove all RTD lead connections.
3. Attach the calibration test equipment as shown in Figure 3-6. Make
terminal connections using miniature banana plugs. Use simulated lead
resistors only if necessitated by long lead wire lengths, as discussed above.
NOTE
If using RTD configurations other than the 3-wire design shown in Figure 3-2,
refer to Figure 2-6 on page 2-6 for the correct wiring.
4. Determine the RTD resistance at the desired base- and full-scale
temperatures. For Calibration Code 1 (see Table 5-5), obtain these
resistances from Table B-1.
5. Turn the power on.
6. Set the decade box to the resistance corresponding to the desired base
temperature. Adjust the zero potentiometer until the output is 0.8 V for
Model 444LL or 1.0 V for Model 444LM.
7. Set the decade box to the resistance corresponding to the desired full-scale
temperature. Adjust the span potentiometer until the output is 3.2 V for
Model 444LL or 5.0 V for Model 444LM.
8. Repeat steps 6 and 7 until you obtain both the zero- and full-scale readings
without adjusting the span and zero potentiometers. Complete this process
more quickly by noting the full-scale reading before readjusting the span
pot, using the span pot to overshoot the desired reading by 20%, and then
using the zero pot to readjust the full scale reading.
9. Disconnect the decade box and the readout. Reconnect the RTD and power
leads. Replace the terminal cover.
10. Mark the correct range in the “Calibration” space on the nameplate.
FIGURE 3-6. Low-Power
Transmitter Calibration
Diagram.
444-0218A
444LL and LM Transmitter
Decade Box
DVM
dcPower
Source
Lead Simulator Resistors
(If required)
Load Resistors ➀
(If required)
+
–
–
+
➀Transmitters are calibrated
at the factory with a 220 K ⍀ load.