48
O&M Manual
Rev F (8/17)
Part 7 – Calibration
7.1 PAA Calibration
Once power is applied, the sensor must be given time to stabilize. This is best done by following
the zeroing procedure below. Establishing a stable zero is critical to the proper operation of the
monitor. A complete calibration will include zeroing and spanning the sensor. It is generally
unnecessary to set the zero at every calibration; however, it should be done during the initial
installation.
7.11 PAA Zero Cal
PAA sensors have extremely low offset currents at zero. For this reason, it is normally sufficient
to simply leave the zero at the factory default of 0.0 nA. As an alternative, an electronic zero can
be set by disconnecting the sensor from the cable and performing steps 3-5 below.
The steps below assume that the sensor has been prepared in accordance with 5.1 PAA
Sensor Preparation, earlier in this manual. Note that the 8 hour waiting time in step 2 below is
not required if the monitor has been running for 24 hours prior to zeroing. If the unit has been
running with the sensor connected, the sensor will normally return to a stable zero within 15
minutes.
1. Connect the sensor to the electronics by plugging the cable plug into the receptacle on the
top of the sensor.
2. Place about an inch of water in a small beaker or other convenient container and immerse
the tip of the sensor. The water used need not be distilled, but it must not contain PAA. For
submersible sensors, submerge the entire sensor in a bucket of PAA free water. Allow the
sensor to sit undisturbed for at least 8 hours.
3. Scroll to the CAL menu section using the MENU key and press ENTER or the UP arrow key.
Cal PAA will then be displayed.
4. Press the ENTER key. The screen will display a flashing 1-Ref for span calibration or a 2-
Zer for zero calibration. Using the UP arrow key, set for a 2-Zer zero calibration and press
ENTER.
5. The system now begins acquiring data for the sensor zero calibration value. As data is
gathered, the units for sensor current in nanoamps (nA) and temperature may flash. Flashing
units indicate that this parameter is unstable. The calibration data point acquisition will stop
only when the data remains stable for a pre-determined amount of time. This can be
overridden by pressing ENTER. If the data remains unstable for 10 minutes, the calibration
will fail and the message Cal Unstable will be displayed.
6. If accepted, the screen will display the message PASS with the new sensor zero reading
(offset), then it will return to the main measurement display. If the calibration fails, a message
indicating the cause of the failure will be displayed and the FAIL icon will be turned on. The
range of acceptable value for sensor offset is -25nA to +25 nA. Should a FAIL occur,
carefully inspect the sensor for a tear in the membrane. It will probably be necessary to
rebuild the sensor as described in section 5.1 PAA Sensor Preparation. Should the offset
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