Red Lion LEGEND - Manual (Page 55)

RATE SCALING EXAMPLE (Cont’d):
EXAMPLE #2:
The shaft of a positive displacement pump has a 14 tooth sprocket that is
being sensed by a magnetic pickup. It is known that the unit pumps 810 liters
of water per minute, when the shaft is turning 400 RPM. It is desired to have a
display readout in liters per minute.
With the Legend, it is not necessary to deal with time unit conversions. From
the information given, we know that when the shaft has turned 400 revolutions,
810 liters of water will have been pumped. The first step we need to take is to
calculate the number of pulses that occur when 810 liters have been pumped.
Number of Pulses = # of Rev x Pulses per Rev = 400 Rev x 14 PPR = 5600 pulses.
We now have all the information necessary to scale the rate. The Total
Scaling Factor, “K
T
”, is calculated using Formula #1 as shown below.
K
T
= Display Units ¸ Number of Pulses = 810 ¸ 5600 = 0.144643
It is noticed that there are more significant digits in the Total Scale Factor,
“K
T
”, than there are available for the Scale Factor, “SF”. To acquire the
maximum amount of significant digits for the Scale Factor, Formula #2 is
used and a Scale Multiplier value of 0.1 is selected.
SF = K T
¸ SCM = 0.144643 ¸ 0.1 = 1.4464
The Scale Factor, “SF”, equals 1.4464 (1.44643 rounded to 4 decimal
places). This provides the maximum amount of conversion accuracy possible.
The final step is to select a Rate Conversion Factor. The Rate Conversion
Factor is chosen to be Rate Per Minute as was required.
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