Calibration

Dependend on the code you will have to recalibrate in time intervals; you might as well start with one now.

Your doubts are justified and correct.

It is not possible to effectively calibrate a flow meter in the field and maintain any sort of accuracy.

Other than to program the meter parameters such as range, Engineering Units (EU), scale, etc. there is not any flow meter calibration that should ever be executed in the field.

Accurate calibration of a flowmeter requires a flow bench capable of providing the correct type and quantity of fluid being measured by the application which equates to the meter being removed from the circuit and shipped to a competent calibration facility.

It is possible to use a portable "clamp-on" meter in the field however the odds of having signal error with a clamp-on meter due to system dynamics is very high.

The risk to personnel and equipment dictates that flow meters should be pulled and calibrated regularly with proper documentation kept up to date.

The calibration interval of calibration is dependent on the application and the system dynamics. The harsher the ambient environment, the more volatile the fluid, and/or the greater swing/cycle of control, the more often the metere will need recalibration.

you are exporting ie if it is a custodian transfer ,you may require a proving skid to check & calibrate your flowmeters.

Your meter suppliers may well have a portable master meter that can be inserted into your line in series with your existing meter. This master would hold a current certificate in all probability linked to your national standards. Your existing meter can then be matched to the master and your certification re-validated. You may have to modify your pipework to achieve this but as recalibration will be required throughout the life of the plant, a removable section terminated in flanges where the master can be inserted will be a useful and valuable feature.

Fiscal metering is a whole different ball game to process metering.

Meter accuracy will be described in legislation, not in manufacturer manuals or company directives. In my time with such meters (gas and finished petroleum products), acceptable accuracy was 0.25%.

Also, these meters needed to be 'proved' annually. here are companies that specialise in this work, and also that manufacture and sell meter-proving systems (will require properly trained personnel, and are pretty expensive to purchase).

Right, we always had 3rd party portable prover's come it the petrochemical plants for pipeline meters.

All instrument are factory calibrated before they ship out to the customer. When it reach to your plant and after installed all these instrument you need to do another calibration just to conform all the measurement is correct and accurate.

That is generally true for almost all measuring instrumentation

However, fiscal metering "calibration" is not quite the same.

Firstly, the meters will probably not be of the DP, Magflow, turbine, Doppler or other common instruments used to measure process flows..Local Authorities usually determine/ prescribe, what types of flow meters are acceptable to them. The general idea is that the customer must never be short-changed.

Therefore, the meters are generally of the positive displacement type, and any proven inaccuracy is in the customers favour, not the suppliers'.

See here for gas type provers http://en.wikipedia.org/wiki/Gas_meter_prover, and for liquids, eg only: www2.emersonprocess.com/.../metering systems/provers/.../Provers.a

The common examples of fiscal liquid meters, are the flow meters in your local gas station pumps.