Instruction Manual
Model 755R
directly proportional change in the indicated percentage of oxygen.
Example:
Range, 0% to 5% O2.
Barometric pressure change after calibration, 1%.
Instrument reading, 5% O2.
mum, 500 cc/min. A flow rate of less than 50 cc/min is too weak to sweep out the detector and associated flow system effi- ciently. Incoming sample may mix with earlier sample, causing an averaging or damping effect. Too rapid a flow will cause back pressure that will affect the readout accuracy. The optimum flow rate is between 200 and 300 cc/min.
Readout error = 0.01 x 5% O2 = 0.05% O2.
Fullscale span is 5% O2.
Therefore, the 0.05% O2 error is equal to 1% of fullscale.
Thus, if the exhaust is vented to the at- mosphere, the pressure effect must be taken into consideration. This may be accomplished in various ways, including manual computation and computer correction of data.
d.Operation at Negative Gauge Pres- sures
Operation at negative gauge pressures is not normally recommended, but may be used in certain special applications. A suction pump is connected to the analyzer exhaust port to draw sample into the inlet and through the analyzer. Such operation necessitates special precautions to ensure accurate readout. First is the basic consideration of supplying the standard gases to the analyzer at the same pressure that will be used for the sample during subsequent operation. In addition, any leakage in the sample handling system will result in decreased readout accuracy as compared with operation at atmospheric pressure.
The minimum permissible operating pressure is 5 psig vacuum (34.5 kPa vacuum). Operation of the analyzer below this limit may damage the detector, and will void the warranty.
e.Flow Rate
Operating limits for sample flow rate are as follows: minimum, 50 cc/min; maxi-
Deviation from the set flow should be held to within 10% or 20 cc/min, whichever is smaller. If deviation is held to within these parameters and operating pressure remains constant, zero and span drift will remain within specification limits.
The analyzer should be installed near the sample source to minimize transport time. Otherwise, time lag may be appreciable.
For example, assume that sample is supplied to the analyzer via a
(30.5 m) length of
Sample transport time may be reduced by piping a greater flow than is required to the analyzer, and then routing only the appropriate portion of the total flow through the analyzer. The unused portion of the sample may be returned to the stream or discarded.
f.Materials in Contact with Sample
Within the Model 755R, the following materials are exposed to the sample: 316 stainless steel, glass, titanium, Paliney No.7, epoxy resin,
g.Corrosive Gases
In applications where the sample stream contains corrosive gases, a complete drying of the sample is desirable, as most of these gases are practically inert when totally dry. For corrosive applications consult the factory.
Installation | Rosemount Analytical Inc. A Division of Emerson Process Management |