40
O&M Manual
Rev-H (6/17)
Part 7 – Calibration
7.1
Hydrogen Peroxide 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 H
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O
2
Zero Cal
Hydrogen peroxide 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 1-5
below.
The steps below assume that the sensor has been prepared in accordance with section 5.1,
Sensor Assembly, 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 hydrogen
peroxide. If the sensor is being used for the first time, allow the sensor to sit undisturbed for
at least 4 hours. If the sensor has been in use, 30 –60 minutes is normally enough to
establish a good zero.
3. Scroll to the CAL menu section using the MENU key and press ENTER or the UP arrow key.
Cal H
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O
2
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. 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.
5. 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 -16nA to +16 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 5.4, H
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2
Sensor Assembly. Should the offset
