Owner’s Manual for ONICON Insertion Turbine Flow Meters • September 27, 2001
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SECTION 5.0: ANALOG ADJUSTMENT PROCEDURE
ONICON electronic circuits are designed and tested to ensure long life with minimal drift;
therefore, you should not expect to make regular field adjustments or calibrations. However,
it will be necessary for you to rescale the analog output under the following conditions:
• The turbine was replaced with a new one having a significantly different
meter factor.
• You wish to change the flow rate represented by the analog output.
• An analog output meter is being moved to a different size pipe.
ONICON will do all of these recalibrations at low cost, with a one or two day turnaround.
However, we have included this section for those instances where you cannot return the
meter or simply want to do the work yourself. We will be happy to work through the
procedure with you on the phone, if you desire.
While these adjustments are not complicated, they are crucial to the accuracy of the flow
meter. Therefore, any adjustments should be made only by qualified personnel having an
understanding of flow equations and experience with control systems.
5.1 GENERAL DISCUSSION
ONICON Insertion Flow Meters contain circuitry which measures the velocity of a flowing
stream of water, or water based liquid, by sensing the rotational rate of a freely rotating axial
turbine, which is immersed in the flow stream. As each turbine blade passes a fixed
electrode, an electronic pulse is produced by the circuitry. In the case of single turbine
meters, the pulse rate is then calibrated in terms of the number of pulses per gallon in
whatever size pipe the user has selected. This number is called the METER FACTOR. For
example an Insertion Flow Meter might have a meter factor of 31.3 PPG (Pulses Per Gallon) in
3” pipe. This is the calibrated frequency output signal
.
Dual turbine meters are basically the same except that the pulse rates from the upper and
lower turbines are electronically averaged and the calibration is done using this average
output signal.
This frequency output signal can be used directly by some data acquisition systems. Other
systems require an analog representation of flow rate. For these systems the frequency output
signal is processed by the optional analog output card and another calibration is then done on
the 4-20 mA and 0-10 V analog output signal.
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