OPERATION OF IAQRAE
2-15
2.9 Integrated Sampling Pump
The IAQRAE includes an internal integrated sampling pump
with programmable high and low pump speed settings:
A
low pump speed
of ~300 cc per minute is the factory
default. This rate increases battery life by about 5%. (See
Section 4.5.9 Change Pump Speed).
In some cases, it is better to program the monitor to a
high
pump speed
of ~400 cc per minute, which is required for
vapors that are especially reactive or easily absorbed by
instrument surfaces. Such vapors include, but are not limited
to: Cl
2
, PH
3
, NH
3
, HCN, and semi-volatile organic compounds
like diesel fuel and jet fuels. Some suggestions for monitoring
heavy organic compounds are listed below:
•
Remove the water trap filter for normal calibration and
operation, which increases the pump speed.
•
Use inert connecting or sampling tubing, such as Teflon
®
instead of Tygon; make tube connections as short as
possible.
Pump Duty Cycle
The duty cycle function allows the user to control the time the
pump is one for a specified ten-second period. A 70% duty
cycle means that the instrument turns the pump on for seven
seconds, and then turns the pump off for three seconds. (See
Section 4.5.8 Change Pump Duty Cycle)
Currently, users may only set the duty cycle from 50% (five
seconds) to 90% (nine seconds) with 10% (one-second)
increments. Decreasing the duty cycle gives the instrument
more time to clean its PID lamp, reducing lamp contamination,
which slows the rate of signal degradation. It also reduces
pump wear and filter contamination, and saves battery power.
Under certain conditions, the duty cycle is automatically
disabled, meaning that the pump is always one. The pump duty
cycle is disabled when the PID reading is higher than 2.0 ppm
and is enabled when the reading drops below 1.6 ppm. The
duty cycle is also disabled during system warm-up, PC
communication, calibration, in diagnostic mode, or when any
sensor (including CO
2
or toxic gas) is in alarm condition.
