Teledyne 4020 – Hydrocarbon analyzer (special version for automatic background gas switching) - Manual (Page 27)

Total Hydrocarbon Analyzer Operational Theory
Teledyne Analytical Instruments 9
2.2.3 Fuel and Blanket Air Systems
The fuel and blanket air systems use similar components. 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; except for instruments using hydrogen as
the sample gas. In this case, the sample is used as fuel and the valve is
located in line with the sample port. See Figure 1-1 for a flow schematic
for instruments equipped with AutoCal valves and Figure 1-2 for
instruments without the AutoCal option.
2.2.4 Flame Ionization Detection Cell
The 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. The cell is located at the left hand
front area inside the enclosure for easy access. See Figure 2.1.
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 1-3).
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.