Preparation for Installation  35 
 
Housing Purge during Operation 
Purge gas flow:  max. 20 l/h (constant) at the instrument inlet 
Positive pressure of 
purging gas: 
p
e
 = 2 to 4 hPa 
With a purge gas flow of 20 l/h at the instrument inlet, the purge gas flow 
at the instrument outlet due to leakage will amount to approx. 5…10 l/h. 
Housing Purge during Operation when Measuring Flammable Gases 
The housing has to be purged with nitrogen. Purge gas flow 1…20 l/h. 
The purge gas flow must be monitored at the purging gas outlet. 
Housing Purge in the Fidas24 
The housing purge is implemented in the Fidas24 gas analyzer in such a 
way that a part (approx. 600…700 l/h) of the instrument air is conducted 
continuously through the housing as purging air. This ensures that a 
flammable mixture cannot form in the housing in the event of a leak in the 
combustible gas feed path. 
The housing purge is always active if compressed air is switched on, 
even if the instrument air valve is closed.