Method of measurement

The most common measuring systems for gas detection are Semiconductive, Electrochemical, Catalytic and Infra-red absorption. The systems have different advantages and disadvantages and vary a great deal in costs.

 

Advantages and disadvantages:

Measuring system Advantages Disadvantages

Ammonia
(NH3)

HFC
(HCFC, CFC)
and blends

Flammable
(HC)

Carbon dioxid
(CO2)

Semi-conductive/
chemosorption

 

- long service  life and
  long-term  stability
- low price  and low
  maintenance  cost
- suitable down  to -30oC

- limited  selectivity
- Limited measuring range

 

Yes

Yes

Yes

 

Electrochemical

 

- medium price
- high selectivity

 

- short service  life (normally  1-3 years)
- Needs recalibration  after exposure to high  concentrations
- limited  measuring
range
- high  maintenance
cost
- not suitable  at sub-zero  temperatures,

unless heated

Yes

 

Yes

 

Catalytic

 

- medium price
- high selectivity
- can accurately register

and record high concentrations

- not suitable for low
concentrations
- needs recalibration after exposure to high concentrations
- not suitable  if there are large fluctuations
in temperature and/or
humidity

Yes

 

Yes

 

Infra-red absorption

 

- high  selectivity
- long service  life
- wide  measuring  range
- great  accuracy

- high price  and high
  maintenance  cost
- large size
- not suitable at sub-zero temperatures,
unless heated

Yes

Yes

Yes

Yes

Charge carrier
injection

 

- medium price
- suitable for use in harsh
  conditions
- high selectivity
- wide measuring range

- short service life (approx.  2 years)

Yes

 

 

 

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