Operation
EGM-4 Operator's Manual – Version 4.19
- 29 -
With the CPY-3 only, the atmospheric pressure Annnn is replaced by the PAR reading
(Qnnnn).
If the EGM-4 is fitted with the optional humidity/temperature sensor, then these measured
parameters are also displayed.
Use the 8/X key to scroll round Displays 2,3 and Standard
To save the measured data at any time, press key Y.
To return to the Main Menu simply press the N key when either Display 2 or 3 is shown.
System Equilibrium
The EGM-4 is an absolute analyzer. In order to work with open-type chambers, an internal
solenoid (built into the chamber) switches every 30 seconds to select either the reference or
analysis sample gas stream for measurement. Therefore, a minimum of 45 seconds must
elapse before valid data is available. However, this is not the time taken to get to equilibrium
which depends on the chamber volume and the flow rate.
For example, with the CFX-1 the effective volume between the Reference and Analysis
sampling points is approximately 2.2 litres :
System Response Time (minutes) = Chamber Volume (2.2litres) / Flow Rate (litres/minute)
So at a Flow Rate of 1litre/minute, System Response Time = 2.2 minutes
Assuming the system is perfectly mixed then there is an exponential approach to equilibrium:
63% of final value achieved in 1 System Response Time
86% of final value achieved in 2 System Response Times
95% of final value achieved in 3 System Response Times
98% of final value achieved in 4 System Response Times
Calculation Of Fluxes For CFX And CPY Chambers
Both the CFX-1 and CPY-3 chambers use Honeywell mass flowmeters that are calibrated at
STP which is 0
o
C and 1013mb. Results are given in
µ
mol m
-2
s
-1
for CO
2
and in mmol m
-2
s
-1
for H
2
O.
Convert the flow (V) measured in ml min
-1
at STP through the chamber with an exposed area
of (A) cm
2
to mol m
-2
s
-1
(Molar Volume at STP is 22.414 l.)
= ( V x 10000 ) / ( A x 22.414 x 1000 x 60) = (V / A ) x 7.436 x 10
-3
With a CO
2
differential between the inlet and outlet of
∆
C ppm, the CO
2
flux is:
∆
C x (V / A ) x 7.436 x 10
-3
µ
mol m
-2
s
-1
and with an H
2
O differential between the inlet and outlet of
∆
H mb, the H
2
O flux is:
∆
H x (V / A ) x 7.436 x 10
-3
mmol m
-2
s
-1
.
For CO
2,
to convert to g CO
2
m
2
h
-1
, multiply by 0.1584.
For H
2
O, to convert to g H
2
O m
2
h
-1
, multiply by 64.87.
