Teledyne 4020 - Hydrocarbon analyzer - Manual (Page 24)

Operational Theory Model 4020
Teledyne Analytical Instruments 8
The basic analyzer consists of an isothermal chamber containing the
pressure regulators, pressure gauges and flow restrictors. The
temperature within the chamber is maintained at 125°F by a heating
element. The regulated temperature of the chamber insures stable gas
flow. An optional AutoCal module is available which when fitted,
mounts inside the instrument enclosure and integrates with the sample
system. It allows convenient switching between sample and calibration
gases. When installed, it is part of the isothermal chamber. The bypass
flow is also controlled from this optional panel.
2.2.1 Input Porting
The analyzer is equipped with ports for the introduction of air, fuel,
zero, span, and sample gas.
2.2.2 Sample Flow Control System
Stable sample flow is achieved by maintaining a constant pressure
across a restrictor through the use of a back-pressure regulation system,
which includes an adjustable regulator, pressure gauge, throttle valve,
and flowmeter. The throttle valve and flowmeter are included so that the
bypass flow required by the back-pressure regulator can be limited.
Without these controls, a high sample point pressure would result in
unnecessary sample waste through the back-pressure regulator.
The components of the system are arranged so that no dead volume
is present in the sample path to the detector cell. This guarantees rapid
response to changes in hydrocarbon concentration—a fact that can be
demonstrated when zero and span gas are exchanged during the
standardization procedure.
The restrictors used in the system look alike; however, they are not
interchangeable.
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