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2.20

2.11 Calibration gas sample connection

If your analyser has the optional internal auto calibration solenoids then the

appropriate calibration gases must be connected to the instrument at the appropriate

ports on the manifold. If no auto calibration manifold is fitted or the external

autocalibration option is used then the calibration gases should be connected to the

sample gas port by external means. These should be delivered to the xentra at the

same pressure and flow rate as the sample gas.

WARNING

Internal autocal is unsuitable for use with toxic samples.

If toxic samples are present, the maximum pressure to the analyser must be

limited to 5 psig by means of a suitable release system.

Two calibration mixtures are required to perform the low and high calibrations of the

transducers fitted. The analyser software may be configured to specify which of the

two gases should be used as low gas for each transducer. The other will then be

the high gas for that transducer. It is possible for the low calibration gas mixture of

some transducers to function as the high calibration gas for other transducers and

vice versa.

The gas mixtures recommended for calibration of the instrument will depend on the

gas components measured by the transducers fitted to the gas stream and the

measurement ranges of the transducers. The recommended gases are limited by

the long term storage stability of the components of the mixture. Certain gas

mixtures should be avoided as these will not be stable with time. For example gas

mixtures containing O

, N

and NO are not stable and should not be used.

Table 2.10 shows gas components recommended in the two gas mixtures needed.

Table 2.11 shows the recommended concentration of the gas components in the

mixture. For example, the recommended gas mixtures for a xentra 4900 analyser

fitted with a paramagnetic transducer, NO Gfx transducer and standard sensitivity

CO transducer would be as follows:-

Calibration gas 1

CO 200 vpm

Air Balance

Calibration gas 2

NO 100 vpm

Balance

Servomex SERVOPRO 4900 User Manual

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