Features
 
The APHA-370 uses a combination of the flame ionization detection method and selective-combustion.
This gives it the advantage of the single-detector method plus the ability to perform continuous measurements, free of zero-drift, for THC, NMHC, and CH4. The design gives great stability and high sensitivity (0-5 ppm F.S.).

The APHA-370 has a relative-sensitivity correction function for CH4 and NMHC.

All the necessary features are built right into a single rack-sized instrument, including a catalytic unit for selective combustion (i.e., an NMHC cutter); a cataytic unit for generating reference gas and auxiliary combustion air (standard); and a sampling pump. The only supplemental gas required is H2.

Principle

The flame ionization detection method (FID) — used in combination with the selective-combustion system — utilizes the ionization that occurs as the result of the high-temperature energy from combus-tion at the tip of the burner jet when organic carbon compounds are introduced into the hydrogen flame. The hydrogen flame is located between two elect-rodes.
When an electrical voltage is applied across these electrodes a minute ion current proportional to the hydrocarbon concentration is produced. This current is monitored by a low leakage amplifier, giving a voltage readout for THC. To measure CH4 the sample gas is passed through the selective catalytic combustion unit (the NMHC cutter), which oxidizes NMHC without oxidizing CH4. This is shown as A below. B represents the THC concentration measured without passing the gas through the NMHC cutter. Thus B - A will give the concentration of NMHC. The final concentration value is calculated using a relative-sensitivity correction coefficient, k, as shown below.
CH4 Concentration A
NMHC Concentration k (B - A)
THC Concentration A + k (B - A)


Specifications