Procedure - Zeroing The Sensor - Emerson Rosemount Analytical HART 5081-A-HT Instruction Manual

MODEL 5081-A
9.2 PROCEDURE — zEROING THE SENSOR
1. Place the sensor in a fresh solution of 5% sodium sulfite (Na
trapped against the membrane. The current will drop rapidly at first and then gradually reach a stable zero
value. To monitor the sensor current, go to the main display. Press DIAG followed by NEXT. The SenSor Cur
prompt appears. Press ENTER to view the sensor current. Note the units: nA is nanoamps; mA is microamps.
The table gives typical zero values for Rosemount Analytical sensors.
Sensor
499ADO
499ATrDO
Hx438 and Gx448
A new sensor or a sensor in which the electrolyte solution has been replaced may require several hours (occa-
sionally as long as overnight) to reach a minimum current. DO NOT START THE ZERO ROUTINE UNTIL THE
SENSOR HAS BEEN IN ZERO SOLUTION FOR AT LEAST TWO HOURS.
CALIBRATE
sensor 0
EXIT NEXT ENTER
CALIBRATE
0 at 0 . 05
EXIT ENTER
CALIBRATE
time delay
EXIT ENTER
CALIBRATE
0 done
EXIT
52
Zero Current
499ATrDO sensors usually do not require zeroing. However,
<50 nA
the zero current of a new sensor should ALWAyS be checked.
<5 nA
<1 nA
2. Press CAL on the remote controller.
3. The SEnSor O prompt appears. Press ENTER.
4. The screen shows the value (in units selected in Section 7.5.3) below
which the reading must be before the zero current will be accepted.
Assume the units are ppm. The screen shows 0.02. Therefore, the read-
ing must be below 0.02 ppm before the zero will be accepted. For a
499ADO sensor 0.02 ppm corresponds to about 50 nA. To change the
zero limit value, see Section 7.8.3. Press ENTER.
The number shown in the main display may change. During the zero
step, the previous zero current is suppressed, and the concentration
shown in the main display is calculated assuming the residual cur-
rent is zero. Once the transmitter accepts the new zero current, it is
used in all subsequent measurements.
5. The tiME dELAy message appears and remains until the zero current is
below the concentration limit shown in the previous screen. If the current
is already below the limit, tiME dELAy will not appear. To bypass the
time delay, press ENTER.
6. O donE shows that the zero step is complete. Press EXIT.
7. Press RESET to return to the main display.
CALIBRATION — OxyGEN
SO ) in water. Be sure air bubbles are not
2 3
NOTE
SECTION 9.0