Analytical Industries GPR-1535 GB Trace PPM Oxygen Transmitter - Manual (Page 15)

Advanced Instruments Inc.
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Recommendation: Zero calibration, see Determining True Zero Offset below, is recommended only for online analyzers
performing continuous analysis below 5% of the lowest most sensitive range available with a ppm analyzer, e.g. analysis below
0.5 ppm on the 10 ppm range, or below 0.1% (1000 ppm) with a percent analyzer.
Determining True Zero Offset: Allow the transmitter approximately 24 hours to stabilize with flowing zero gas as evidenced by a
stable reading or horizontal trend on an external recording device.
Once the zero offset adjustment is made, zero calibration is not required again until the sample system connections are
modified, or, when installing a new oxygen sensor. As a result, zero calibration is not practical and therefore not recommended
for higher ranges or portable analyzers.
Span Calibration: Involves adjusting the transmitter electronics to the sensor’s signal output at a given oxygen standard.
Regardless of the oxygen concentration of the oxygen standard used, a typical span calibration takes approximately 10 minutes.
The amount time required to get the analyzer back on line for normal use is influenced by a.) the level of oxygen analysis
anticipated during normal operation (also determines the initial analyzer selection), and, b.) whether the sensor is new or has
been in service at ppm levels.
General guidelines for analyzers to come online following span calibration and exposure to a zero/purge/sample gas with an
oxygen content below the stated thresholds:
¾ measurements above 1000 ppm or 0.1% require less than 3 minutes
¾ measurements above 100 ppm (parts-per-million analyzer) require less than 10 minutes
¾ measurements below 10 ppm (part-per-million analyzer) require 20 minutes if the sensor has been in service at ppm levels
¾ measurements below 10 ppm require 60 minutes if the sensor is new or has been air calibrated assuming the
zero/purge/sample gas has an oxygen concentration below 1 ppm
Recommendation: For 'optimum calibration accuracy' calibrate with a span gas approximating 80% of the full scale range one
or two ranges higher than the full scale range of interest (normal use) to achieve the effect illustrated on Graph A and Example
1. Always calibrate at the same temperature and pressure of the sample gas stream.
Note: Calibrating with a span gas approximating 10% of the full scale range near the expected oxygen concentration of the
sample gas is acceptable but less accurate than ‘optimum calibration accuracy’ method recommended – the method usually
depends on the gas available. Calibrating at the same 10% of the full scale range for measurements at the higher end of the
range results in magnification of errors as discussed in Graph A and Example 1 and is not recommended. Of course the user can
always elect at his discretion to accept an accuracy error of +2-3% of full scale range if no other span gas is available.
Air Calibration: Because the sensor takes longer to recover from exposure to air than span gas, see General Guidelines above,
air calibration is recommended only 1) when a certified span gas is not available, 2) when installing and replacing a ppm oxygen
sensor or 3) to verify the oxygen content of a certified span gas.
Based on the inherent linearity of the electrochemical galvanic fuel cell type oxygen sensor enables the user to calibrate the
analyzer with ambient air (20.9% oxygen) and operate the analyzer within the stated accuracy spec on the lowest most
sensitive range available with the analyzer – there is no need to recalibrate the analyzer
with span gas containing a lower oxygen concentration.
Calibrating either a ppm analyzer with ambient air on the CAL or 0-25% range meets the
80% criteria discussed in the Recommendation above.
Calibration Procedures:
Certified Gas Cylinder for Zero or Span Calibration:
Calibration: The user is responsible for calibration gases and regulating the pressure to 5-
30 psig, controlling the flow rate to 1-2 SCFH or .5-1 liter per minute and the plumbing to
and from the Glove Box Housing Assembly.
1. Install the sensor in the Calibration Mode of the Glove Box Housing Assembly (right).
2. Use metal tubing to transport the span gas to the sensor.
3. The main consideration is to eliminate air leaks and ensure the sample gas tubing
connections fit tightly into the 1/8” male NPT to tube adapter, and, the NPT end is