Analytical-industries GPR-2800 AIS ATEX Oxygen Analyzer Manuel d'utilisateur télécharger pdf (Page 26)

Advanced Instruments Inc.

Span Calibration

Maximum drift from calibration temperature is approximately 0.11% of reading per °C. The analyzer has been calibrated at the

factory. However, in order to obtain reliable data, the analyzer must be calibrated at the initial start-up and periodically

thereafter. The maximum calibration interval recommended is approximately 3 months, or as determined by the user’s

application.

Calibration involves adjusting the analyzer electronics to the sensor’s signal output at a given oxygen standard, e.g. a certified

span gas with an oxygen content (balance nitrogen) approximating 80% of the next higher full scale range above the intended

measuring range is recommended for optimum accuracy, see Calibration and Accuracy.

Recommendation – based on the inherent linearity of the galvanic oxygen sensor air calibrate the analyzer as described

below when installing and replacing the oxygen sensor (exception UHP and MS versions of the Pico Ion Sensor); or, to verify the

oxygen content of a certified span gas; or, when a certified span gas is not available (immediately following air calibration

reintroduce a gas with a low oxygen concentration to expedite the return to % level measurements).

Caution: Prematurely initiating the SPAN CALIBRATION key before the galvanic fuel cell sensor based analyzer reading has

stabilized can result in erroneous readings. For example, to assure an accurate air calibration when installing a new % oxygen

sensor from its packaged oxygen free atmosphere allow the oxygen sensor 2-3 minutes to reach equilibrium with the oxygen

content of the ambient air surrounding it before pressing the SPAN CALIBRATE key. A % oxygen sensor that has not been

allowed to reach equilibrium will generate a lower current output than a % oxygen sensor that has reached equilibrium.

Pressing the SPAN CALIBRATE key before the % oxygen sensor has reached equilibrium forces the micro-processor to

prematurely read the (erroneous low) current output of the % oxygen sensor and introduce larger (erroneous) than required

electronic gain adjustment and display (also erroneous) CALIBRATION SUCCESSFUL message to the user. The error will become

evident when a zero gas with a low oxygen concentration is introduced into the % analyzer to purge it down below 10 %. The

analyzer reading may stop and appear to stabilize as high as 1800 % – giving the user the (erroneous) impression there is a

problem with the % oxygen sensor when in fact the problem lies with the user’s failure to follow the recommended calibration

procedure.

Required Components: Refer to Installing Span Gas section above.

¾ A clean source of instrument air or certified span gas cylinder with an oxygen concentration, balance nitrogen,

approximating 80% of the full scale range above the intended measuring range.

¾ Regulator to reduce pressure to between 5 and 30 psig.

¾ Flow meter to set the flow between 1-5 SCFH,

¾ Suitable fittings and a 4-6 ft. in length of 1/8” dia. metal tubing to connect the regulator to the flow meter inlet

¾ Suitable fitting and a 4-6 ft. in length of 1/8” dia. metal tubing to connect to the flow meter vent

¾ 1/8” male NPT to tube adapter fitting to connect the 1/8” dia. metal tubing from the flow meter vent to the mating male

quick disconnect fitting supplied with the GPR-2800AIS.

Procedure – Instrument Air or Span Gas Calibration:

The user must ascertain that the oxygen reading (actually the sensor’s signal output) has reached a stable value within the

limits entered below before entering the span adjustment. Failure to do so will result in an error.

1. This procedure assumes a span gas under positive pressure and is recommended for a transmitter without an optional

sampling pump, which if installed downstream of the sensor should be placed in the OFF position and disconnected so the

vent is not restricted during calibration.

2. To assure an accurate calibration, the temperature and pressure of the span gas must closely approximate the sample

conditions.

For calibrat

ion purposes, use of the AUTO SAMPLE mode is recommended. However, the user can select the full scale

MANUAL SAMPLE RANGE for calibration as dictated by the accuracy of the analysis required – for example, a span gas with

an 80 % oxygen concentration with the balance nitrogen would dictate the use of the 0-100 % full scale range for

calibration and a 0-10 % measuring range. Select as described above.

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

5. Advance the reverse shade cursor using the ARROW keys to highlight AUTO SAMPLE.

6. Press the ENTER key to select the highlighted menu option.

7. The following displays appear:

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 41 42

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Analytical-industries GPR-2800 AIS ATEX Oxygen Analyzer Manuel d'utilisateur Page 26

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