Technical Overview:
The Bridge Exhaust Gas Analyzers use a mix of technologies to make gas measurement. NDIR (Non-Dispersive InfraRed) technology is used to measure CO, HC, and CO2. Chemical Sensors are used to measure O2 and NOx. The NDIR technology is temperature compensated, and has shown itself to be very time-stable. It will not require recalibration in the field unless the measurement altitude is changed by more than 3,000 ft from the calibration point.
Chemical sensors are additionally temperature and time unstable, and will require more frequent calibration to maintain accuracy. The O2 sensor is calibrated on ambient air (which has a very stable amount of O2 in it) whenever the analyzer is Zeroed – every ½ hour. Due to the ready availability of O2calibration gas – the O2 channel never has to be calibrated.
The only gas channel which uses a chemical sensor that does not have a readily available source of calibration gas is the NOx channel in the Model 900503. This sensor degrades in NOx sensitivity at 5% to 10% per year – so it will require re-calibration in the field at 6 month intervals to stay within the +/- 5% analyzer accuracy specification.
Field Calibration Recommendations:
NOTE:
While there is no intrinsic need to re-calibrate the analyzers above – certain agencies stipulate annual calibration certification as good manufacturing practice. To aid the customers in meeting this standard of practice, Bridge offers annual calibration and certification service on an as-needed basis. Contact Bridge for current prices and to arrange this service.
Initial Calibration for High Altitude Use:
The analyzer is pre-calibrated at the factory in such a way that it will be within the accuracy specifications given for the full temperature range up to an altitude of 3,000ft above seal level. At altitudes above 3,000 ft, it is recommended that the customer perform an initial field calibration for all gases at the altitude of use. Once this initial on-site calibration is performed, the analyzer can be operated for +/- 1,500 ft altitude change and will still remain within specification.