2 replies to this topic

[curious_cat]

We have a flowmeter (0-1000 L/hr scale) installed whose spec. sheet mentions a guaranteed accuracy of 2% of the Full Scale Deflection. (for flows greater than 100 L/hr)

 

The unit also has an integrated electronic totalizer. The debate among some of us is whether this implies (by logic or convention) that the totalizer too would be 2% accurate? Or does the totalized flow accuracy have to be independently mentioned by the vendor. (I haven't seen them mention it)

 

 

e.g. if after 20 minutes  of flow the totalizer reads 150 Litres, can it be assumed that (in a legitimately performing instrument) the true metered quantity would be 150 +/- 6.6 Litres? (6.6 and not 3 because the reference used is FSD not actual reading)

 

Also, in general cases, where not mentioned explicitly would totalized accuracy be better or worse than the dial accuracy or can it be either way. 

 

 

Comments?

[fseipel]

Yes, totalizer should have identical accuracy but there are exceptions.  If the totalizer is external to the meter, there may be some additional error due to resolution of the ADC and signal noise, and whether its 4-20 mA signal was ever calibrated and matches the span and time units of the flowmeter.  Also filtering can have an impact.  Some meters alternately send a pulse signal to an external totalizer.  The main issue I've seen is low-flow cut-off; if there is no low flow cutoff, and totalizer integrates, say, 5 L/hr, even when there's no flow, it's necessary to either configure such a cutoff or to reset totalizer prior to feeding and record its final value.  I find it useful in control system to, say, alarm if pump is on, but meter isn't reading within typical range after, say, 20 or 30 seconds.  If you want higher accuracy, I'd recommend putting a drum or tank on a scale, and either discharging it or filling into it, the process fluid,and correct the meter and totalizer.  This will also confirm their operation.

Edited by fseipel, 06 October 2013 - 03:26 PM.

[curious_cat]

Thank you @fseipel! That helps!

 

Totalizer is integrated here in the instrument. Your ADC errors etc. are all possibly there but just within the vendor's black box. 

 

We use it as a feed measuring device for a batch reactor so it is indeed zeroed after & before every batch.