PPM–400ST Formaldehyde Meter Operation Manual
2 TECHNICAL INFORMATION
2.1 Principle of Operation
Electrochemical
Formaldehyde
Sensor
The PPM–400ST Formaldehyde Meter uses proven
electrochemical sensing technology for determining
the concentration of formaldehyde in air samples.
The instrument contains a formaldehyde sensor
formed from two noble metal electrodes and a
suitable electrolyte.
When air is drawn into the sensor by the internal
sampling system a small voltage is produced as a
result of the oxidation of formaldehyde at one of the
catalytically active electrodes. This voltage is
directly proportional in magnitude to the
concentration of formaldehyde in the sample.
The voltage is amplified and converted to a digital
signal for a microprocessor which in turn
manipulates the signal to give a result on the
instrument display in “parts-per-million by volume”
(ppm). The microprocessor also converts the result
to “milligrams-per-cubic metre” (mg/m
3
) and
stores the results to non-volatile memory.
All the electronic systems are based on modern,
integrated circuitry employing the latest surface
mount technology to ensure that the PPM–400ST
Formaldehyde Meter is an exceptionally robust and
reliable instrument.
2.2 Interference
Alcohols &
Aldehydes
As with other portable detection equipment, the
meter is not totally specific to formaldehyde alone.
The instrument is susceptible to interference from a
small range of other chemicals. Other aldehydes
and alcohols such as methanol and ethanol in the
atmosphere can cause cross-interference effects.
8
