MSA SIRIUS Instruction Manual page 53

The carbon monoxide channel in the SIRIUS instrument is equipped with internal and
external filters. The purpose of these filters is to protect the CO sensor from acid gases
(H S, SO , etc.) and from the hydrocarbons that the instrument is intended to measure,
2 2
including the calibration gas, isobutylene. In normal use, an interferent signal for calibra-
tion or bump checking the instrument should not be observed on the CO channel.
However, exposure to large amounts of certain hydrocarbons (either long exposure times
or high concentrations) can overwhelm the filter and appear as signals on the CO channel.
In normal operation, after the hydrocarbon exposure is ended, the filter is designed to
outgas absorbed hydrocarbons at a rate that will not cause a signal on the CO channel.
However, if the unit is exposed to high temperature (>40 °C), this desorption rate increases
and spurious signals may be observed on the CO channel due to gassing of previously
absorbed hydrocarbons. If this occurs, it may be necessary to replace the CO sensor.
Table 12. HYDROGEN SULFIDE (appropriate models only) –
Typical Performance Specifications
RANGE
RESOLUTION
REPRODUCIBILITY**
RESPONSE TIME
* See Table 5. Instrument specification, NOTE
** See Table 14. PID Typical Performance Specifications NOTE
200 ppm H S
2
1 ppm H S for 3 to 200 ppm H
2
± 2 ppm H S or 10% of reading, whichever is greater
2
0 to 100 ppm H S ±15% > 100 ppm H
2
(normal temperature range*)
± 5 ppm H S or 20% of reading, whichever is greater
2
(extended temperatur range*)
90% of final reading in 50 seconds with sample line
and probe (normaI temperature range*)
Performance Specifications
S
2
S
2
8
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