3-1 OVERVIEW
Preparatory to operation, a familiarization with Figure 3-1 (page 3-3) is recom- mended. This figure gives locations and summarized descriptions of operating adjustments of the Model 755R Oxygen Ana- lyzer.
3-2 OPERATING RANGE SELECTION
The Model 755R is designed to operate on a single, field-selectable range. A new range may be selected any time the analyzer application changes or any time calibration may require a range change.
To select the operating range, reposition the jumper shown in Figure 3-1 (page 3-3) to the desired location. Each position is labeled as to its fullscale range. Only the analog output (voltage and optional current) is affected by range selection. The digital display always reads 100% oxygen.
3-3 STARTUP PROCEDURE
Inject a suitable on-scale gas (not actual sample) through the analyzer. Turn power ON. If digital display gives overrange indi- cation, the probable cause is the suspension in the detector is hung up. To correct this condition, turn power OFF, tap detector compartment with fingers, wait 30 seconds, turn power ON.
When on-scale reading is obtained, allow analyzer to warm-up for a minimum of one hour with gas flowing. This warm-up is necessary because a reliable calibration is obtainable only after the analyzer reaches temperature stability. Moreover, the resultant elevated temperature will ensure against condensation within, and possible damage to the detector assembly. After warm-up, the digital display or recorder should give stable, drift-free readout. If so,
proceed to Section 3-4 below. Otherwise, refer to Section 6, Maintenance and Serv- ice.
3-4 CALIBRATION
Calibration consists of establishing a zero calibration point and a span calibration point (see Table 3-1, page 3-4). Zero and span calibration should be performed on the range that will be used during sample analysis. In some applications, however, it may be desirable to perform span calibration on a range of higher sensitivity (i.e., more narrow span) and then move the jumper to the desired operating range. For example, if the operating range is to be 0 to 50% oxygen, span calibration may be performed on the 0 to 25% range to permit use of air as the span standard gas.
a.Calibration with Zero and Span Standard Gases
NOTE:
The same flow rate must be maintained for zero, span, and sample to avoid measure error. The exhaust is vented to the atmosphere to avoid back pressure. The following procedure is based on the standards in Table 3-2 (page 3-6). Performance specifications are based on recorder output.
Set Zero Calibration Point
Inject nitrogen zero standard gas through analyzer at suitable flow rate, preferably 250 cc/min. Allow gas to purge analyzer for a minimum of three minutes.
Adjust ZERO control so that the reading on the digital display or recorder is zero
