2.7 Affection on Measurement from Pressure
The pressure in the Gas Chamber becomes different from the atmospheric pressure whiling sampling the gas. As a
result, the indication is not accurate. Or, if an instant pressure change occurs in the Gas Chamber or the Reference
Chamber, the indication might go wrong. (If these symptoms occur, perform the AIR CAL right away.) Therefore, take
care about the following points:
Do not plug the GAS IN or GAS OUT while gas is feeding.
Do not attach and detach sampling tube/absorption tube while gas is feeding.
Keep the pressure of GAS IN, GAS OUT, and REF. OUT equal to the atmospheric pressure when the indication is
read.
Read the indication after the gas flow stops.
CAUTION:
When concentration change occurs suddenly on the FI-21, correct reading cannot indicate.
Absorption tube is also for stabilizing the temperature of the sampling gas. Therefore, equip an
absorption tube on the GAS IN whenever the measurement is performed.
CAUTION:
Whenever measurement starts, confirm if the AIR CAL value is displayed after fresh air is sampled
enough. If the AIR CAL. Value is not indicated (or even if [AIR CAL CAUTION] is not displayed),
perform the AIR CAL procedures by correct method.
An example of measurement when the pressure of the sampling point is higher than the atmospheric pressure:
Make an inlet (a) as the drawing below. Open and shut the stop valve to feed the gas to the instrument,
instead of turning the pump on and off. Read the indication after shutting the valve off and the gas flow totally
stops. Flow rate at Inlet (a) should be 300 to 400mL.
GAS OUT should be at the atmospheric pressure and the REF. OUT should face with fresh air.
