Teledyne 4020 – Hydrocarbon analyzer (special version for automatic background gas switching) - Manual (Page 26)

Operational Theory Model 4020
Teledyne Analytical Instruments 8
separate calibration must be performed on each sample/background
combination. The calibration parameters are stored internally and are
appropriately applied when the user selects the specific background gas
in use. See Section 4.7.2 Background Gas Selection.
Note: The user must supply the necessary valves and any
associated switching equipment for delivering the correct
sample/background gas combination to the analyzer.
This special 4020 Analyzer includes the ability to automatically
select between two background gases (N
2
and O
2
). Additional display
screens have been added and electrical modifications performed to
implement and control the automatic background switching capability of
this instrument.
Note: The user must supply the necessary valves and any
associated switching equipment for delivering the correct
sample/background gas combination to the analyzer.
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.