GDC-350 Operation Manual
5909-9000 Rev 1
27
5. CALIBRATION
NOTE:
During any calibration procedure, if the instrument sounds with
repetitive beeps, the sensor is not settling within tolerance (1% for catalytic
and solid-state sensors, 20% for electrochemical sensors). Contact
Bacharach support for additional information.
5.1. Calibration Specifications
Gas: Calibration span gases should be at least ±5% accuracy and have a current date
stamp. Gas generators should have a current dated cell installed. Service personnel
should flow zero emissions air or 20.9% volume oxygen before attempting to null
adjust toxic gas sensors. In some cases N
2
(nitrogen) can be substituted for zero air.
Nitrogen is required to null (zero) oxygen (O
2
) and carbon dioxide (CO
2
) sensors.
Exception: If the service person is confident of air quality and is careful (do not exhale
in the direction of the oxygen sensor being serviced while span adjusting), oxygen in
the breathing environment can be used as a fairly accurate source of span gas
(20.9% volume). It is not recommended to use this procedure for span adjustments of
oxygen sensors.
Regulators and Flow: Calibration gases that are lighter than or the same weight as air
(CO, O
2
, etc.) should be flowed at 0.5 LPM. Gases heavier than air (NO
2
, etc.) should
be flowed between 0.5 and 1.0 LPM. Fixed flow regulators provide more accuracy.
Gases should be flowed over the sensor for at least 2.5 to 4.0 minutes. Carbon
Monoxide sensors settle out very quickly, but sensors for reactive gases (NH
3
, etc.)
will take longer to stabilize to the calibration gas. All cylinder regulators supplied by
Bacharach use a fixed flow orifice.
Adapters: The proper calibration adapter should be utilized to allow the gas to
properly diffuse around the sensor. They are available from Bacharach. A
humidification chamber must be utilized for all solid-state sensors except ammonia.
This is also available form Bacharach. (See table on page 34 for ordering
information.)
5.2. Frequency Recommendations
Sensor Types / Applications
Calibration Frequency
Parking garage detectors
Once every 12 months
OHS (Occupational Health and Safety) applications
Once every 6 months
For the purposes of safety in OHS applications, sensors should be gas tested (e.g.,
bump tested) once every month to confirm response.
IMPORTANT:
In applications where life safety is critical, equipment should
be calibrated quarterly or on a more frequent basis. Bacharach is not
responsible for setting safety practices and policies. Safe work procedures
including calibration policies are best determined by company policy,
industry standards, and local codes.
