Teledyne GFC-7001E - Trace CO Analyzer - Manual (Page 77)

Optional Hardware and Software Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 77
5.9. CARBON DIOXIDE SENSOR (OPTION 67A)
The optional CO
2
sensor allows the GFC 7001E/EM to measure both CO and CO
2
simultaneously. This option
includes a CO
2
sensor probe, a Logic PCA that conditions the probe output and issues a 0-5 VDC signal to the
analyzer’s CPU that is used to compute the CO
2
concentration.
The GFC 7001E/EM receives this input, scales it based on the values of the CO
2
_SLOPE and CO
2
_OFFSET
recorded during calibration (see Section 9.7.2).
Figure 3-4 shows the location of the Sensor Probe and PCA within the GFC 7001E/EM.
The CO
2
sensor assembly itself does not have any serviceable parts and is enclosed in an insulated canister.
5.9.1. CO
2
SENSOR RANGES AND SPECIFICATIONS
Table 5-6: CO
2
Sensor - Available Ranges
OPTION NO. RANGES ANALYZER MODEL(S)
67A 0-20% GFC 7001EM
Table 5-7: CO
2
Sensor Specifications
Accuracy at 25˚C 0.02% CO + 2% of reading
Linearity 0.5 % of full scale
Typical Temperature Dependence -0.1% FS / ˚C
Long Term Stability <+15 % FS / 2 years
Response time 20 seconds
Warm up time 5 minutes
Power consumption 2.5 watts
5.9.2. THEORY OF OPERATION
5.9.2.1. NDIR measurement of CO
2
The optional CO
2
sensor is a silicon based Non-Dispersive Infrared (NDIR) sensor. It uses a single-beam, dual
wavelength measurement method.
An infrared source at one end of the measurement chamber emits IR radiation into the sensor’s measurement
chamber where light at the 4.7 μm wavelength is partially absorbed by any CO
2
present. A special light filter
called a Fabry-Perot Interferometer (FPI) is electronically tuned so that only light at the absorption wavelength of
CO
2
is allowed to pass and be detected by the sensor’s IR detector.
A reference measurement is made by electronically shifting the filter band pass wavelength so that no IR at the
CO
2
absorption wavelength is let through.