3. Is the sensor properly wired to the transmitter?
4. Is a ground loop present? Refer to Process pH grossly wrong or noisy
8.4.9 Simulating input currents - dissolved oxygen
To check the performance of the transmitter, use a decade box to simulate the current
from the oxygen sensor.
1. Disconnect the anode and cathode leads from terminals 13 and 14 and connect a
decade box as shown in Figure 8-11.
It is not necessary to disconnect the RTD leads.
Simulate dissolved oxygenFigure 8-11:
2. Set the decade box to the resistance shown in the table.
Sensor Polarizing voltage Resistance Expected current
499ADO -675 mV 34 kΩ 20 µA
499ATrDO -800 mV 20 kΩ 40 µA
Hx438 and Gx448 -675 mV 8.4 MΩ 80 nA
3. Note the sensor current. To view the sensor current:
a. Go to the main display and press DIAG.
b. Press NEXT.
SEnSor Cur appears in the display.
c. Press ENTER.
The display shows the sensor current.
d. Note the units.
µA is microamps; nA is nanoamps.
Diagnostics and troubleshooting
112 Rosemount 5081
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