APPENDIX D. CHARACTERISTICS IN LIQUID SERVICE

APPENDIX D

CHARACTERISTICS IN LIQUID SERVICE

Each electrical pulse generated by the turbine flow transducer represents a discrete volume of fluid. The

relationship between the pulses and a given volume of fluid is given by the meter calibration factor. This meter

calibration can be referred to as the "C" factor, and is expressed as "Gallons Per Minute/Pulses Per Second". The

degree to which these pulses represent the given volume of fluid at various flow rates determines the transducer's

accuracy and repeatability. The variation experienced in this pulse-volume relationship over a specified flow range

defines the transducer's linearity. This "ideal" performance is generally achieved when the kinematic viscosity of the

liquid is in the range of 0.5 to 2 centistokes. If the flowmeter is used with liquids having viscosities greater than 2

centistokes, the "C" factor will be increased. This effect is sometimes referred to as "viscosity drag" or "viscosity shift".

This shift can also be shown in a plot of flow rate versus output frequency (See Figure 14). Note that the higher the

viscosity, the greater the shift. (Figures 13 & 14 are exaggerated and considered to be examples only).

Since it is desired to use turbine flowmeters with several liquids, it is necessary to determine a universal viscosity

calibration curve (See Figure 15). From this curve one can determine the performance of the flowmeter when used with

liquids that cover a large viscosity range. Data needed for the universal viscosity curve is determined through

calibrations using several different viscosities. This can be one liquid at different temperatures or several different

liquids. The data points, when plotted on one set of coordinates, will overlap and form a smooth composite curve. Using

this curve the performance of the flowmeter can be determined for any frequency (Hz) or viscosity (V) if the Hz/V value

is within the range of the data used in determining the curve. The correlation of data obtained from actual calibration and

data taken from the universal curve when using oils and hydrocarbons is 0.25%.

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