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Instruction Manual
IM-106-5500, Original Issue
August 2005
1-5
CCO 5500
The basic expression from which the gas concentration in the gas is
determined is:
This parameter Y is then smoothed, linearized and compensated for effects of
path length and flue gas temperature, to produce a measurement of gas
concentration in the flue gas.
Error Compensation The accurate determination of gas concentration depends on the
measurement of the radiation levels received by the detectors. Any error in
that measurement caused by detector drift will produce errors in the
determination of the gas level. In order to maintain accuracy, it is necessary to
be able to compensate for such drifts. In the CCO 5500 analyzer a technique
of continuous calibration adjustment is used.
The operating cycle of the instrument is in two parts. First, measurements are
obtained from the two detector outputs D1 and D2. The calibration cell,
containing pure CO, is then positioned in the sight path and the two detector
outputs are measured again to give readings E1 and E2.
From the basic scale shape equation:
and from the calibration equation
thus substituting in the scale shape equation
The two ratios E1/D1 and E2/D2, being derived each from one detector, are
independent of any detector drift, thus making the instrument output
independent of any drift or change in detector gain characteristic.
This operating routine, giving measurements first of D1 and D2 and then, with
the calibration cell in position, of E1 and E2, is repeated continuously and
provides an effective continuous calibration update to enable accuracy to be
maintained at all times.
Y = G - K. D2/D1
Where D1 = the reference output from the detector
D2 = the live output from the detector
G = a scaling factor (1600)
K = a constant, known as the zero correction
factor, set so that when there is zero
measurement gas in the duct, Y = 0
thus, K = G. D1(0)
D2 (0)
Y = G - K. D2/D1
Yo = G - K. E2/E1
or K = (G - Yo). E1/E2
Y = G - (G - Yo). E1/E2. D2/D1