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Turbine Flow Meter Manual 05/13 - 0721-1 / 13518
Page 27
SECTION 5.0: ANALOG ADJUSTMENT PROCEDURE
ONICON electronic circuits are designed and tested to ensure long life with minimal drift. It
should not be necessary to make field adjustments or calibrations. It may, however, be necessary
to rescale the analog output under the following conditions:
•
The turbine was replaced with a new one that has a significantly different meter factor.
•
It is necessary change the full scale flow rate for the analog output.
•
An analog output meter is being moved to a different size pipe.
ONICON will clean, test and recalibrate the meter for a small fee. One or two day turnaround
service is available when required. The information in this section is provided only for those
instances where you cannot return the meter service and factory calibration. ONICON will
provide assistance when performing this procedure via the telephone, if necessary.
While these adjustments are not complicated, they are crucial to the accuracy of the flow meter.
Adjustments should only be made by qualified personnel having an understanding of flow
equations and experience with control systems.
5.1 GENERAL DISCUSSION
ONICON insertion turbine flow meters measure the velocity of the fluid flowing in the pipe.
Proprietary electronic impedance sensing circuitry detects the rotation of a freely spinning 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 for whatever size pipe the user
has selected. This number is referred to as the METER FACTOR. For example an insertion flow
meter might have a meter factor of 31.3 PPG (Pulses per Gallon) in 3” pipe. The meter factor is the
calibration factor used to define the calibrated frequency output signal provided by all ONICON
turbine meters. This frequency output signal can be used directly by some data acquisition
systems. Other systems will require additional signal conditioning. In those cases, ONICON uses
this signal to drive our analog and digital outputs.
Dual turbine meters provide the same calibrated frequency output except that the pulse rates from
the upper and lower turbines are electronically averaged and the calibration is done using this
average output signal.
5.2 ANALOG ADJUSTMENT PROCEDURE
This procedure adjusts both 4-20 mA & 0-10 V output signals. It is limited to meters with serial
numbers 115692 and higher. Contact ONICON for assistance if your meter’s serial number is
below 115692.
5.2.1 Equipment Required
• Multimeter: Capable of measuring voltage and current (mA)
(4½ digit true RMS meter recommended)
• Pulse Generator: 0-15 volt square pulse (0-10 volt minimum)
0-500Hz minimum operating range
Recommended resolution 0.01Hz (0.1 Hz minimum)
• Power Supply: 24 VAC or VDC ±4V
