EGM-5 Operation Manual V. 1.04 70 support@ppsystems.com
Injection Process
The injection process is a technique used to measure the concentrations of small samples of gas, usually
collected in sampling jars and transferred to the EGM-5 with a syringe. The injection process is an
improvement over static sampling and yields more reliable and consistent results.
Measurement Principle
The concentration of CO
2
in a gas sample is calculated by injecting the sample into a fixed flow of gas
with a known CO
2
concentration (the baseline CO
2
level) and integrating the resulting CO
2
measurements
until they return to baseline. This is similar to the Pulse Tracer Gas Technique used for HVAC duct flow to
infer the unknown flow rate by measuring the concentration of a known mass of tracer gas injected into
the duct over time. In our case, the gas flow rate F is known, the syringe volume V is known, but the
sample (or tracer gas) concentration is unknown.
The concentration in the syringe is calculated as:
=
(
)
=
_
_
60
Where
CO
2 INT
(ppm) = calculated CO
2
concentration inside syringe (“integrated” CO
2
)
CO
2_ b
(ppm) = baseline CO
2
readings before the measurement phase (averaged over 10
readings)
CO
2_m
(ppm) = CO
2
readings during the measurement phase
Δt (s) = sample interval, typically 1 second
F (ml min
-1
) = flow rate
V (ml) = syringe volume
The process consists of two phases: Baseline Phase and Measurement Phase. The Baseline Phase
establishes a baseline measurement of CO
2
concentration by passing CO
2
-free gas through the EGM-5
and calculating the average concentration over 10 measurements at a 1-second interval. Upon
completion of the Baseline Phase, the instrument will enter the Measurement Phase. In this phase the
sample is slowly injected, and the measured CO
2
concentrations are integrated over the duration of the
Measurement Phase. Any gas with a known, constant CO
2
concentration can be used as a baseline, but
a gas with zero CO
2
concentration can be readily produced with an absorber column filled with soda lime.
Sample Injection Kit (Part No. ACS037)
PP Systems offers a Sample Injection Kit (Part No. ACS037),
which includes a fully assembled and leak-tested injection
port with 4 spare septa, as well as an absorber column to
establish a zero baseline.
The syringe is user supplied (not included with the kit) and
the soda lime is not included with this part but it is included
with the EGM-5 as standard.
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