Servomex NanoTrace DF-760E, Инструкция по эксплуатации

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122 DF-760E Sample Gas Preparation and Delivery
8.4.3 Pressure Effects on Oxygen Sensor Performance
If the analyzer is not vented to atmosphere, the oxygen sensor pressure is influenced by the
conditions downstream of the analyzer. A recalibration under your operating conditions
may be desirable to remain within the stated accuracy specifications. However, in most
cases the error introduced is relatively small, and may not affect the process application.
Sample gas line lengths, fittings and bends should be kept to a minimum to maintain low
pressure drops. Larger diameter tubing and fittings reduce pressure drop and also lengthen
response time. In general, 1/8-inch tubing should be limited to 15-foot runs; longer runs
should be made with 1/4-inch tubing.
8.4.4 Sample Outlet Backpressure Effects
It is always recommended to vent the analyzer to atmospheric pressure. However, if a
sample vent or return line is used, attention must be given to maintain a low and consistent
backpressure so as not to affect the flow rate.
The allowable backpressure on the oxygen sensor is ±1 psig. If variations in the vent line
pressure are expected, a sub-atmospheric backpressure regulator should be installed on the
vent line to maintain an even backpressure on the analyzer. Consider the regulator’s
pressure drop (typically 1 psi) when designing the sample vent system in order to stay
within the ±1 psig pressure limits at the sensor.
When not venting the analyzer to atmosphere, it is also suggested to install a fairly high
resolution pressure gauge immediately at the analyzer outlet.
8.4.5 Flammable Sample Gas
There is nothing within the analyzer sample system that can ignite a flammable sample
gas. However, it is critical to ensure that the sample gas does not escape from the sample
system into the analyzer enclosure, or the room, where ignition is possible.
Also, the analyzer enclosure can be purged with nitrogen, or the entire Analyzer can be
mounted in a purged enclosure, so that any sample gas that escapes the plumbing is
diluted. Servomex does not provide an analyzer equipped with these protective features.
Note that these methods may not be compliant with local or national requirements in your
country. Ensure that you comply with all necessary regulations and standards.
8.4.6 Sample Gas Temperature
Gas temperature should not exceed 50 °C (122° F), nor should it fall below 0° C (32° F).
Gas temperature can be controlled by passing the gas through 5 to 10 feet of metal tubing
that is within the recommended sample temperature. Because of its low thermal mass, the
gas sample quickly reaches the gas sample line temperature.
The analyzer has software to correct the sensor output for sensor temperature changes.
Temperature compensation adjustments apply to temperature drift only when the oxygen
level is below 10 ppb. Ideally, the analyzer should be operated at a nominal temperature of
70° F. Calibration temperature should be close to operating temperature. If the analyzer is
to be operated at an average ambient temperature outside 65° F to 80° F, it should be
recalibrated at the operating temperature for optimal performance.