Impact / Impact Pro / Impact Pro IR Operating Instructions
39
4�9 Calibration
The accuracy of the Impact instrument should be checked with known concentration
calibration gas before each day’s use. If any sensor fails recalibrate the Impact
before using, or replace the cartridge. It is recommended that the instrument be
calibrated at least every 6 months. The calibration interval for the CO
2
sensor shall
not exceed 1 month.
The Impact instrument provides three methods of calibration, offering flexibility for
the user. Flow calibration is the traditional method and can be performed, following
instructions displayed on the instrument itself (Section 4.9.2 Flow Calibration
– Instrument), or when the instrument is connected to a PC via a Base Station, on
the PC display (See Section 4.9.3 Flow Calibration – PC). An alternative method
for instruments fitted with a combination of oxygen, flammable, carbon monoxide
and hydrogen sulfide sensors only is to use the Enforcer accessory. For all other
gases the flow calibration method must be used.
CAutIoN
Use of non-standard calibration gas and/or calibration components when calibrating
the Impact can lead to dangerously inaccurate readings.
The calibration should be carried out in a well-ventilated area to avoid
contaminants.
Do not calibrate the electrochemical sensor CO
2
channel if CO
2
is indicated in
clean air after the apparatus has been exposed to CO
2
concentrations above the
upper limit of the measuring range. In this case leave the instrument in clean air
overnight before calibration.
4�9�1 Contaminants
Oxygen sensors may be affected by prolonged exposure to carbon dioxide, and it is
recommended the Impact not be subjected to use in atmospheres containing more
than 25%v/v carbon dioxide (CO
2
). Oxygen sensors may read high in the presence
of carbon dioxide.
Flammable sensors may be affected by exposure to Silicone substances; organic
phosphorus containing compounds and halogenated organic compounds. Although
the flammable sensors used in Impact and Impact Pro have a high resistance to
Hydrogen Sulfide (H
2
S) poisoning some loss in sensitivity should be expected.
Therefore it is strongly recommended repeated gassing with H
2
S or gas alarms
on the H
2
S channel should be followed by checking and if necessary re-calibration
of the Flammable sensor. The sensors on average will lose approximately 20% of
their sensitivity when subjected to forty applications of H
2
S for a period of 1 minute
each.
The toxic sensors are designed to be gas specific, minimizing the effects of common
cross-interfering gases. The table below summarizes the effect of various gases on
the Carbon Monoxide and Hydrogen Sulfide sensors.
Summary of Contents for Impact
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