Flowmeter installation and maintenance must be performed correctly to achieve
the stated performance of a flowmeter. The effects of improper installation and
maintenance vary from a reduction in accuracy to a flowmeter that does not operate
at all. Attention to installation detail, piping requirements, and maintenance
are critical to flowmeter performance.

In order to obtain the best accuracy (i.e. lowest measurement uncertainty).
Flowmeters should be calibrated and used in piping arrangements that do not
introduce external effects. Suppliers usually calibrate meters in long straight pipes
where the velocity profile is fully developed. However they are very frequently
installed in non-ideal piping so their performance may change from that detailed
on the certificate of calibration.

Departures from the calibration certificate data are not just limited to piping
effects. Other external influences can cause flowmeter performance to change,
such as radio frequency interference, ambient temperature effects or humidity
variations. There are many recorded instances where large errors are present due
to such effects. Sometimes the flowmeter fails to function at all in extreme cases.
Changes in performance can be reduced through regular maintenance.

Effects that cause departure from the ideal have been termed influence effects or
installation effects. This chapter looks at practical considerations for reducing
installation effects through good installation and maintenance procedures.

Piping Considerations

Flowmeter Operation

It is preferred to install flowmeters in vertical piping with flow upwards. However,
this is not always practical. Liquid (gas) flowmeters require that the flowmeter
be full of liquid (gas) to achieve accurate measurement. Often, liquid (gas)
flowmeters must be located at the lowest (highest) point in the piping to achieve
this end. Some flowmeters require special orientation, such as in the case of the
magnetic flowmeter, which requires that the electrodes be mounted in the horizontal
plane.