Supplementary Measurements
Two Point Flow Sensor Calibration Using the New Lin Function
The MC4000 menu contains two scaling parameters;
SCALE
and a scaling divisor referred to as the
DSCALE
. The MC4000 flow
sensor output signal is a frequency that is proportional to the rate of flow and the monitor uses the frequency information to
calculate volumetric flow rate and total flow . The raw frequency from the turbine flow sensor requires scaling by a constant
in order to achieve a display reading in the required flow units . The MC4000 refers to this constant as the
SCALE
defined
as follows .
SCALE =
Maximum Frequency
Maximum Flow Rate
The
DSCALE
setting is used to shift the decimal point, and is particularly useful when the
SCALE
parameter is a very small
number in the case of small, high frequency turbine flow sensors .
Calculated flow readings in the MC4000 use the following formula .
Display Reading =
DSCALE
Input Frequency x SCALE
Example
A typical 1 in . turbine flow sensor would have the following characteristics .
Maximum Flow
=
80 gpm
Maximum Frequency =
765 Hz
The scale factor calculation is:
SCALE =
765 Hz
80 gallons
= 0.1046
The value for this sensor entered into the
SCALE
parameter would be 0 .1046 . In this case a
DSCALE
value of 1 .000 would give
correct readings on the MC4000 display .
Using a larger value for
DSCALE
offers higher resolution and is especially useful when the
SCALE
value has several leading
zeroes in it .
Example
A small turbine flow sensor has the following full scale values .
Maximum Flow
=
7 gpm
Maximum Frequency =
2632 Hz
SCALE =
2632 Hz
7 gallons
= 0.0026596
Because of display limitations, better results are obtained by multiplying the
SCALE
value by 1000 and using a
DSCALE
value
of 1000 .
Page 14
February 2015
TST-UM-00017-EN-03
