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APPENDIX A
Calibration of Meters with Manual and ATC Calibrators
For the purpose of adjustment, some Smith meters
are equipped with a calibrator utilizing two overriding
clutches and an eccentric. By adjusting the amount of
eccentricity the calibrator can be made to vary the drive
ratio between the meter and the register by a maximum
total of 11 per cent.
This calibrating means is used for adjusting for
manufacturing
variations,
variations
in
operating
conditions, differences in viscosity of product metered,
variations in testing methods and testing equipment as
well
as
for
providing
automatic
temperature
compensation.
The nature of the device is such that a correction
impulse is imparted to the calibrator output shaft once
during each revolution. The correction impulse causes
a momentary acceleration of the register which will
result in errors and erratic tests if not taken into account.
It is important when calibrating a meter that the
volume of the calibrated prover be a multiple of the
increment of correction of the meter. For example, a
prover for 5:1 gallon geared meters should be 200, 205
or 210 gallon capacity and not 203 or 207. For 1:1
barrel geared meters it is essential that the prover be
calibrated in even 42 gallon barrels.
The reason for the above is evident as each test run
must contain the same number of correction impulses in
order to be absolutely accurate. If the test is started
with the meter register at zero, the register at the end of
the test run should show a quantity divisible by the
number of gallons or barrels delivered for each
revolution of the calibrator, or each correction impulse.
The magnitude of the meter correction is in the
order of 5 or 6 per cent of the volume of meter thruput
per correction input cycle. On a standard 5:1 gallon
geared meter this would be S or 6 per cent of 5 gallons
and on a 1:1 barrel geared meter it would amount to 5 or
6 per cent of 42 gallons. The type of register used is not
necessarily an indication of meter correction frequency,
as a gallon geared meter may be equipped with a
register geared to read in barrels.
It is therefore desirable to have the prover tank of a
volume which conforms to even increments of full
barrels as well as increments of 5 gallons, as for
example, 30 barrels or 1260 gallons. A prover of this
size makes it possible to test either a gallon geared
meter or a barrel geared meter. By starting and
stopping the meter on an even barrel or five gallon
increment as the case may be and reading the error on
the prover scale, the error due to meter correction
impulse is entirely eliminated.
Many meters with gallon gearing are equipped with
barrel registers and it may be necessary to test these
meters into a barrel calibrated prover. Further, the
prover may be of an odd size, barrels and fractions of
barrels.
Take as an example a prover of 29.3 barrel capacity
being used to test a meter with gallon gearing (5 gallons
per revolution) with a register reading in barrels. The
register will be assembled with 8.4:1 gear ratio.
In a case of this kind the meter calibrator impulse
error can be avoided by following the procedure outlined
below.
Determine the number of gallons contained in the
prover 29.3 x 42 = 1230.6 gallons. Reduce this to the
nearest number divisible by 5 or 1230. Now consider
the volume of the prover 1230 gallons or 29.285 barrels
instead of 29.3 barrels. Make a test run stopping the
meter at exactly 29.285 barrels thereby completing the
full number of correction cycles. Read the error on the
prover scale.
METER GEARING--Metered throughput per revolution of meter output shaft.
A9-37
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