SCALE FACTORS
34
Unit Conversions
In some cases, the measurement system is set up
to measure in one engineering unit but the parts
made are produced in a different engineering unit.
This may be the difference between ounces and
gallons, inches and feet, feet and yards, inches
and millimeters, quarts and liters or any other com-
bination. In these applications, the scale factor
may be chosen from the table given in Figure 28 or
calculated using any standard conversion factor
carried out to four decimal places.
Scaling Pulses Received From Flowmeters or
Other Sensors
Typically, flowmeters generate large numbers of
pulses for each unit of measure. Additionally, the
number of pulses per unit is usually not easily
divisible or massaged to allow a standard counter
to increment in a common engineering unit.
The scale factor to be entered into the counter is
easily calculated by using the formula:
1 (Unit of Measure)
Scale Factor =
Pulses Produced
per Unit of Measure
For example, a flowmeter might produce 146
pulses per gallon of flow. If the counter is to count
gallons of flow, the incoming pulses must be
divided by 146. If the display should indicate whole
gallons of flow accumulated, the scale factor is
determined by:
Scale Factor = 1 / 146 = 0.0068
If the display should rather show gallons and
tenths of gallons, the scale factor may be multi-
plied by 10 to yield 0.0685. (Note that in this case
the decimal point on the counter should be placed
between the first and second digits for proper indi-
cation of units.)
When the output from other sensors must be
scaled, the same formula can be used to calculate
the scale factor. It is sometimes easier to change
the definition of the terms in order to find the scale
factor, however. For example, a quadrature shaft
encoder which produces 600 pulses per revolution
is used to indicate rotation of a shaft. Usually, rota-
tion is given in degrees with 360 degrees per revo-
lution. If the doubled Quadrature count mode is
used, 1200 pulses per revolution are received by
the counter. This results in 3.3333 pulses per
degree of rotation.
Given this information, finding the scale factor nec-
essary for proper operation can be confusing. But
if the terms of the formula are changed as:
Desired Display Value
Scale Factor =
Actual Pulses Received
Filling in the terms the scale factor is found by:
360(Counts Per Revolution)
Scale Factor=1200(Pulses Per Revolution)=0.3000
With the Scale Factor of 0.3000, the display will
indicate 360 degrees per revolution from a 1200
PPR encoder.
Allowing Multiple Parts per Machine Operation
If a single machine operation causes one pulse to
be received by the counter and that single
machine operation produces several parts simulta-
neously, the scale factor is simply the number of
parts produced per pulse. For example, if six parts
are produced per cycle of the machine, a scale
factor of 6.0000 should be entered into the control.
In this example, if one of the six cavities requires
repair and is not producing parts, the scale factor
may be reduced from 6.0000 to 5.0000. This
adjustment can be made without resetting the
counter. The machine must be stopped, the Pro-
gram Inhibit jumper removed if installed, and the
Scale Factor changed. Then the Program Inhibit
jumper may be reinstalled and the process started
up again. This allows in-process service and
adjustment of machine malfunctions without losing
track of how many parts have been produced so
far.
