Detection Cell, Gas Flow Control System

Introduction

2.2.2 Gas Flow Control System

The Piping diagram is in the rear of this manual. A 10 port-switching valve is used to control and direct gas flows to the FID detector. The fixed volume sample loop ensures the same volume of sample injection in the Analyzer every cycle.

2.2.3 Fuel and Blanket Air Systems

Stable flow is achieved by maintaining a constant pressure across restrictors upstream from the cell. Each system incorporates an adjustable pressure regulator, pressure gauge, and restrictor. A flame out light is included to indicate when the flame fails. A fuel shut-off solenoid valve, mounted on the line that supplies fuel, stops the fuel flow in case of flame failure. This valve is located in line with the fuel port.

2.2.4 Flame Ionization Detection Cell

The carrier gas containing sample and fuel are combined within a tee fitting located in the isothermal chamber. The mixed gas is emitted from a burner within the sensor assembly. Blanket air is introduced into the sensor (or cell) by means of a separate fitting that is located in the base section of the assembly. The upper half of the assembly houses the anode-igniter, collector, and flame guard thermistor.

2.3 Detection Cell

The upper section of the stainless steel flame ionization cell houses the cylindrical collector electrode, the high voltage (+260 VDC) anode- igniter coil, and the sensing thermistor of the flame guard circuit (see cell cross-section Figure 2-1).

WARNING: DANGEROUS HIGH VOLTAGE EXISTS AT THE ANODE IGNITER COIL (+260 VDC). DO NOT ATTEMPT TO DISCONNECT THE IGNITER COIL CABLE OR DISASSEMBLE ANY OF THE FLAME IONIZATION CELL COMPONENTS WITHOUT TURNING OFF THE POWER AND DISCONNECTING THE POWER CORD.

The collector is interconnected with the electrometer-amplifier PC board by a coaxial cable. Although the cable and fittings are intended for coaxial service, the cable is actually being used as a shielded single- conductor connection.

Teledyne Analytical Instruments