LumaSense Technologies INNOVA 1316A-2 - Manual (Page 14)

Chapter 1
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BE6021-11 1316A-2 Multi Gas Monitor LumaSense Technologies A/S
Instruction Manual Page 14 of 97
System Board Assembly
The system board assembly is a surface-mount printed circuit board
that includes the digital and analogue electronic components and the
IR detector assembly. The IR detector assembly includes thermopile
IR detectors for the Freon, CO
2
and reference channels. Light passed
through the band pass filters is directed through the thermopile
window to a detector substrate. The substrate has a light-sensitive
coating, which produces a voltage that is proportional to light
intensity. A reference voltage is produced by the reference detector,
which provides an output that varies with light intensity and is not
affected by the sample gas. The detector block temperature
measurement facilitates compensation for IR filter and IR detector
temperature variances. The detector outputs are amplified and sent
through a multiplexer to an ADC converter. The microprocessor
samples the ADC converter output at 200 Hz and derives an
uncompensated digital value representing each gas concentration.
The data are subjected to a compensation routine that provides
adjustment for temperature and pressure variances. The digital value
representing each gas concentration is derived.
1.4.4 The NDIR Temperature Measurements.
The analyzer incorporates several thermistors for the measurement
of temperatures.
IR Detector/Filter Temperature :
A thermistor located in the optical assembly measures the IR
detector and IR filter temperature. It is used as follows:
“Gas law compensation” and detector response compensation during
Freon and CO
2
gas concentration measurement.
Span calibration (via the use of temperature compensated Freon and
CO
2
data).
An “out of range” IR detector/filter temperature condition causes
Freon and CO
2
data to be declared “data invalid.”
In the Module the IR Detector/Filter Temperature is monitored to set
the zero request bit as follows:
Zero Request if a ±5°C temperature change has occurred.
Ambient Temperature Out Of Range is set when the IR
Detector/Filter Temperature is not within its allowed range.