Red Lion LEGEND - Manual (Page 55)

COUNTER SCALING EXAMPLE:
EXAMPLE #1:
A flow sensor provides 62 pulses per gallon. Calculate the scaling required to
provide a display reading in gallons. The number of “Display Units” displayed
after 62 pulses have been counted should be 1.
STEP 1 - Calculate the Total Scaling Factor, “K T ”, using Formula #1.
FORMULA #1
K T = Display Units ¸ Number of Pulses = 1 ¸ 62 = 0.016129
STEP 2 - In this application 62 pulses per gallon provides more than enough
resolution, so the “Number of Count Edges” (Selected in the Program Counter
Module) is set to a value of X1. With an “NCE” value of 1, the remaining
scaling factor required is still 0.016129.
FORMULA #2
K R = K T
¸ NCE = 0.016129 ¸ 1 = 0.016129
STEP 3 - To provide maximum scaling accuracy, a “Scale Multiplier” value is
chosen that will give the maximum amount of significant digits in the Scale
Factor. A value of 0.01 will result in a Scale Factor Value of 1.6129.
FORMULA #3
SF = K R
¸ SCM = 0.016129 ¸ 0.01 = 1.6129
EXAMPLE #2:
A quadrature Rotary Pulse Generator that provides 100 pulses per revolution
is coupled to a feed roll that is 2.5 feet in circumference. It is desired to read in feet
with display resolution to the nearest hundredth of feet (0.01).
In this application, the requirement is for the display to read in hundredths of a
foot. A 2.5 ft. distance will equate to 250 “Display Units” (hundredths). The
“Number of Pulses” for 2.5 ft. is 100, as stated.
From the information obtained, the Total Scaling Factor, “K T ”, can be
calculated, using Formula #1.
K T = Display Units ¸ Number of Pulses = 250 ¸ 100 = 2.5
With a Total Scaling Factor, “K T ”, of 2.5, it can easily be seen that for every
pulse that is input, the display will increment by 2.5 display units (hundredths).
The application requires resolution to the nearest hundredth of a foot. To get
higher resolution, Quadrature x4 Input Response Mode is selected. This will
provide four times the resolution. Using Formula #2, and 4 for the “Number of
Count Edges”, the Remaining Scaling, “K
R ”, is calculated.
K R = K T
¸ Number of Count Edges = 2.5 ¸ 4 = 0.625
At this point, it can be seen that the Remaining Scaling Factor value of 0.625
will fit into the Scale Factor value range without losing any significant digits or
scaling it any further. Because of this, the Scale Multiplier (SCM) factory set value
of X1 is used, and 0.6250 is programmed directly in for the Scale Factor, “SF”.
SF = K R
¸ SCM = 0.6250 ¸ 1 = 0.6250
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