5 non-linearity correction – Yokogawa 415 Steam and Gas User Manual

Page 35

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3.5 NON-LINEARITY CORRECTION

3.5.1 Digital Input Linearity Correction

Non-linearity correction enables the instrument to correct for known
non-linearities if the flowmeter. This feature is not selectable for analog flow
inputs.

Up to 10 frequencies and scaling factors can be programmed. Data on the
flowmeter non-linearity can usually be supplied by the flowmeter manufacturer in
the form of a Calibration Certificate, and is the result of individual tests on a
flowmeter over a range of flowrates. The Certificate will list a number of
flowrates or frequencies with the measured K-factor (eg. pulses per gallon or
litre) at each flowrate.

The following diagram graphs the change in scaling factor with frequency for a
hypothetical flowmeter. The heavy black line represents the actual scaling factor
of the flowmeter, while the light black line is the approximation used in the
instrument.

Linear Interpolation is used between points on the curve, except for Factor 1
which maintains a constant value between Frequency 1 and the maximum input
frequency.

Operation 33

Scaling Factor

Fact 6

Fact 5

Fact 4

Fact 3

Fact 2

Fact 1

Frequency

Freq

6

Freq

5

Freq

4

Freq

3

Freq

2

Freq

1

Max

Frequency

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