PortaSens II
Gas Detector
C16 Leak Detector
O & M Manual
Rev. G, 11/07
- 25 -
CALIBRATION
Calibration of a
PortaSens II
is a little different than calibrating many other types of
detectors. While the procedure you will follow is similar to other detectors, the result of the
calibration is storage of calibration constants in the sensor module, not in the detector. The C16
can use a broad range of sensor modules, and the calibration constants for each module are
loaded into the detector as soon as the sensor is plugged in and the unit is turned on.
A primary advantage of this calibration data storage method is that sensor module
calibration is independent of the detector being used. This means that sensor modules can be
calibrated separately and simply plugged in to any C16 detector. Sensor modules can be
removed from the detector and sent to ATI for factory calibration using special gas generation
equipment unavailable to most users. Because stable gas standards for many gases are not
readily available or are very expensive, this factory calibration technique can be much more
economical in the long run. Contact ATI or your ATI representative for details on factory
calibration service for sensor modules.
While factory calibration of sensor modules is a good alternative, many users may wish to
perform their own calibrations, or at least be able to verify proper calibration. Calibration of the
PortaSens II
is recommended approx. every 6 months in normal use. If the unit is used very
infrequently, yearly calibration should be sufficient. This can be done easily provided that the
user has a reliable gas standard to use for the calibration procedure. If calibration gas is
available, adjust the sensor zero and span as described below. Even if the user does not intend
to perform span adjustments, it is a good idea to periodically check the sensor zero and reset to
correct for any minor zero drift. Checking the zero every few months is recommended.
ZERO ADJUSTMENT
Proper adjustment of instrument zero is essential for accurate measurement.
ZERO
ADJUSTMENT SHOULD ALWAYS BE DONE PRIOR TO MAKING SPAN ADJUSTMENTS
. A
proper zero is set by exposing the sensor to an air sample know to be free of the target gas or
any interfering gases, and adjusting the LCD display to a value of zero. Because the C16 is a
portable instrument, exposing the sensor to a zero air sample is often very easy. Many (probably
most) indoor working areas are likely to be free of the types of gases normally measured.
However, background concentrations of a few gases such as CO, oxides of nitrogen, or ozone
can be found in many areas, especially on smoggy summer days. An air conditioned office area
will normally be free of most interferences. If in doubt, use zero air for setting the zero.
Supplying zero air and span gas to a C16 detector requires the use of a bypass “T” fitting
inserted into the manifold as shown in Figure 5 on Page 26. The internal sample pump draws
approximately 400 cc./min. through the sensor manifold. Zero and calibration gas cannot be fed
into the pump under pressure, so it is necessary to flow gas through the bypass “T” at a rate that
is higher that the internal pump is using. A lower flow rate will result in low values due to dilution.
Zero air and span gas must flow through the bypass at a rate of 500 cc./min. or higher.
