Analytical-industries GPR-1200 ATEX Portable Trace PPM Oxygen Analyzer Manuel d'utilisateur télécharger pdf (Page 17)

Zero Calibration

In theory, the galvanic fuel cell type oxygen has an absolute zero meaning it produces no signal output when exposed to an

oxygen free sample gas. In reality

, expect the analyzer to generate an oxygen reading when sampling a zero gas due to:

¾ Contamination or quality of the zero gas

¾ Minor leakage in the sample line connections

¾ Residual oxygen dissolved in the sensor’s electrolyte

¾ Tolerances of the electronic components

The Zero Offset capability of the analyzer is limited to 50% of lowest most sensitive range available with the analyzer.

As part of our Quality Control Certification process, the zero capability of every ppm analyzer is qualified prior to shipment.

However, because the factory sample system conditions differ from that of the user, no ZERO OFFSET adjustment is made to

analyzer by the factory

Recommendations:

¾ Zero calibration 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 0.05 ppm on the 0-1 ppm range, 0.5 ppm on the 10 ppm

range, or below 0.1% (1000 ppm) with a percent analyzer.

¾ Determining the true Zero Offset requires approximately 24 hours to assure the galvanic fuel cell sensor has consumed the

oxygen that has dissolved into the electrolyte inside the sensor while exposed to air or percentage levels of oxygen. Allow

the analyzer to stabilize with flowing zero gas as evidenced by a stable reading or horizontal trend on an external recording

device. For optimum accuracy, utilize as much of the actual sample system as possible.

¾ Zero calibration is not practical and not recommended for portable analyzers or measurements on higher ranges. However,

satisfying these users that the zero offset is acceptable for their application without the 24 hour wait can be accomplished

by introducing a zero gas (or sample gas with a low ppm oxygen concentration) to the analyzer. Unless the zero gas is

contaminated or there is a significant leak in the sample connections, the analyzer should read less than 100 ppm oxygen

within 10 minutes after being placed on zero gas thereby indicating it is operating normally.

¾ Zero calibration should precede span calibration.

¾ Initiate the DEFAULT ZERO and DEFAULT SPAN procedures before performing either a ZERO or SPAN CALIBRATION.

¾ Caution: Prematurely initiating the ZERO CALIBRATION function can result in negative readings near zero.

¾ Once the zero offset adjustment is made, zero calibration is normally not required again until the sample system

connections are modified, or, when installing a new oxygen sensor.

Procedure:

Refer to Span Calibration below for the detailed procedure. Differences include the displays illustrated below, substituting a

suitable zero gas for the span gas and the time required to determine the true zero offset of specific oxygen sensor, analyzer

and sample system combination.

Default Zero:

The software will eliminate any previous zero calibration adjustment and display the actual the signal output of the sensor at

any specific oxygen concentration. For example, assuming a zero gas is introduced, the display will reflect an oxygen reading

representing the previous zero calibration adjustment (s) as described above. Performing the DEFAULT ZERO feature allows the

user to test the sensor’s signal output when exposed to a specific oxygen standard (without removing the sensor from the

sensor housing).

Procedure:

1. Access the MAIN MENU by pressing the MENU key.

2. Advance the reverse shade cursor using the ARROW keys to highlight CALIBRATION.

3. Press the ENTER key to select the highlighted menu option and the following displays appear:

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 34 35

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Analytical-industries GPR-1200 ATEX Portable Trace PPM Oxygen Analyzer Manuel d'utilisateur Page 17

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