PortaSens
III
Portable Gas Leak Detector, Model D16
Operation and Maintenance Manual
Rev-A Feb 2018
- 37 -
Calibration
Sensor calibration is a two-step procedure known as “Zero” and “Span”
that records gas response data in the sensor memory. The D16 reads the
data and uses it to generate accurate gas readings.
“Zero” is the term applied to the sensor output in the absence of the
target (or surrogate
5
) gas. Over time, the sensor zero output may decrease,
resulting in a slightly negative gas concentration reading. Zero calibration
solves this problem by storing the cell’s zero output level in sensor memory,
and subtracting it out when computing the gas reading. Zero calibration is
recommended to be performed, or checked, once every 2-3 months, and
should always be done before “Span” calibration.
“Span” is the term applied to the sensor output in the presence of the
target (or surrogate) gas. The output level, divided by the concentration of
gas applied, is the sensor’s “sensitivity”. Over time, changes in cell chemistry
or diffusion may cause the sensitivity to decrease, causing the D16 to
produce readings lower than actual. Span calibration updates the sensitivity
value in memory, which is then used when computing the gas reading.
Span calibration is recommended to be performed, or checked, once
every 6 months. This period may be extended to one year if the sensor is
used infrequently, and stored appropriately. The concentration of the source
gas is normally between the “Warning” and “Danger” alarm levels for toxic
gas sensors, and 20.9 % for Oxygen sensors (normal atmospheric
concentration).
“Zero” must be done before “Span”.
Factory Calibration Services
Sensors may be returned to the factory for calibration, where they are
calibrated using specialized gas cylinders, blenders, generators, and other
traceable standards that might not be available to most users (most typically
for span calibration). These standards tend to be expensive to acquire and
maintain, which might make factory calibration more economical in the long
run. Contact the factory, or your factory representative, for details on the
certified calibration program for H10 sensors.
5 Gas used in place of the sensor’s target gas as a matter of convenience or safety, to which the sensor is usually more
or less sensitive.
