Teledyne TRACE OXYGEN ANALYZER 356WA - Manual (Page 28)

Teledyne Analytical Instruments 5-6
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flowmeter column or humidifier column.
5.9 Leak Detection 5.9 Leak Detection 5.9 Leak Detection 5.9 Leak Detection 5.9 Leak Detection
The most frequent cause of trouble in trace measurement is leakage.
Tiny leaks which may be unnoticeable can cause serious errors in trace
measurements. One of the principal problems is that air can diffuse into a gas
line through a small leak, even though the gas pressure in the line may
greatly exceed atmospheric pressure.
When a leak occurs in a system where the mass flow velocity is less
than the molecular velocity, gas molecules move in both directions through
the leak. The net flow of a particular gas, e.g. oxygen, will depend on the
relative partial pressure of that gas on each side of the leak. In a sample
having only a few parts-per-million oxygen, there will be a net flow of
oxygen inward unless the sample pressure is many thousands of pounds.
5.9.1 Leak Detection Procedure 5.9.1 Leak Detection Procedure 5.9.1 Leak Detection Procedure 5.9.1 Leak Detection Procedure 5.9.1 Leak Detection Procedure
The procedure outlined here is based on the premise that the leak rate is
independent of sample flow rate.
a) Stop the sample flow to permit oxygen to accumulate at the point
of the leak.
b) After approximately one minute, restart the sample flow. It is
advisable to practice establishing the flow rate to 150 cc/min 150 cc/min 150 cc/min 150 cc/min 150 cc/min., the
reference flow indication on the flowmeter, with one quick turn
of the throttle valve.
c) Simultaneous to restarting the flow, start a stopwatch to measure
the time required for the recorder/meter to respond to the
accumulated oxygen.
d) The following are approximate times for the accumulated oxygen
to reach the cell from various points in the sample path through
the analyzer at 150 cc/min
150 cc/min 150 cc/min 150 cc/min 150 cc/min.
1.5 to 2 seconds Calibrator
3.5 to 3.75 seconds Base of humidifier column*
5.5 seconds Flowmeter
6.5 seconds Metering valve
7.5 seconds Gas connection at rear of analyzer
> than 7.5 seconds Sample connection lines leading to
analyzer
* A leak at this location may indicate a leak in the column or in the
reservoir system.
5.9.2 Cell Leak 5.9.2 Cell Leak 5.9.2 Cell Leak 5.9.2 Cell Leak 5.9.2 Cell Leak