Introduction
EGM-4 Operator's Manual – Version 4.19
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PP Systems is continuously updating its products and reserves the right to amend product
specifications without notice.
Introduction
The EGM-4 CO
2
Analyzer is a portable operated unit that is powered by an internal 12 V, 2.0
Ah lead acid rechargeable battery providing up to 4 hours continuous use or 12V NiMH
rechargeable battery providing up to 8 hours continuous use. For extended operation in the
field, PP Systems can also provide an external power supply cable that will allow you to
connect up to an external 12 V battery. If interested, please contact PP Systems (See
on page 7).
The EGM-4 is a high precision instrument for use in CO
2
monitoring applications such as
greenhouses, environment control rooms, nurseries and laboratories. Long term stability and
accuracy is ensured as a result of our unique “Auto-Zero” technology. The EGM-4 also
features inputs for additional sensors for measurement of humidity, temperature, PAR, O
2
,
soil respiration, soil temperature and canopy assimilation.
Measurement Principle
The EGM-4 CO
2
is a non-dispersive, infrared gas analyzer that features an “
Auto-Zero”
facility. Using infra-red gas analysis techniques, we can readily determine CO
2
(Carbon
Dioxide) concentrations to within a few ppm and instantaneous measurements are possible.
Gases with di-atomic molecules such as CO
2
strongly absorbs photons in the infra-red range.
For CO
2 ,
one region of strong absorption is 4.26 microns. A source emitting strongly at this
wavelength is a light bulb. If this is positioned at one end of a tube and at the other end is
placed a sensor that is sensitive to photons at 4.26 microns, we have a simple infra-red gas
Analyzer. As carbon dioxide is passed down the sample cell, it absorbs some of the infra-red
and the sensor reading decreases. The “
Auto-Zero
” feature, which occurs at regular
intervals, allows for fast warm-up, adaptation to changing ambient conditions and excellent
stability of the CO
2
signal. The action of auto-zeroing minimizes the effects on span (gas
sensitivity) of sample cell contamination, source aging, changes in detector sensitivity and
changes in pre-amplifier gain.
The entire optical bench assembly (i.e. sample cell) is filtered and should never require
replacement.
To ensure proper operation, the EGM-4 MUST always
be operated in a vertical, upright position.
The EGM-4 can be supplied with two different optical benches. One bench is optimized for
measurement of CO
2
in the ranges of 0-1,000 ppm up to 0-30,000 ppm. The other optical
bench is optimized for 0-50,000 ppm and 0-100,000 ppm. All instruments are checked and
calibrated at the concentration specified at time of order to ensure that the readings are < 1%
of that value. When an instrument is reset to its default values (i.e. when the system is
initialised, see
on page 43), it returns to this setting.
It is important to note that the information contained in this documentation normally
refers to the latest firmware (EPROM) which can change over time. We recommend
that all users keep in contact with us from time to time to ensure that they are running
the most up to date system firmware.
