Red Lion LEGEND - Manual (Page 53)

APPENDIX “A” - SCALING FOR COUNT INDICATION
The Legend is factory set to provide 1 count on the display for each pulse that
is input to the unit. In many applications, there will not be a one to one
correspondence between input pulses and display units. In these applications it
will be necessary for the Legend to scale or multiply the input pulses by a scaling
factor to achieve the proper display units desired (feet, meters, gallons, etc.).
There are three different parameters used in scaling the input pulses to the desired
reading. They are: the “Count Scale Factor”, the “Counter Scale Multiplier”, and
the “Number of Count Edges”. The number of count edges is determined in the
Program Counter Module. For example, the number of edges for the
“CNT+DIRX1” mode is one and the “QUAD X4” mode is four. All three are
factored together to provide the Total Scaling that is necessary. The Count Scale
Factor and Scale Multiplier are programmed in the Program Scaling section.
The first step in scaling the counter requires that the “Number of Pulses” per
“Display Units” needs to be obtained. This may require a small amount of
deductive reasoning.
EXAMPLE: A 48-tooth gear is mounted to a 2 ft circumference feed roll in a
paper processing plant. It is desired to totalize the total footage of paper
processed. In this example, the display units will be in feet. A sensor sensing
the gear teeth will provide 48 pulses for each revolution of the feed roll. Each
revolution will equate to a linear distance of 2 feet. The number of “Display
Units” desired will be 2. The “Number of Pulses” per “Display Units” will be
48. When the number of “Display Units” and the “Number of Pulses” have
been obtained, the Total Scaling Factor can be calculated.
The “Total Scaling Factor”, denoted as “K
T ”, is simply the total amount of
scaling required. It is obtained by dividing the “Display Units” by the “Number
of Pulses” as shown in Formula #1 below.
FORMULA #1: K T = Display Units ¸ Number of Pulses
WHERE:
K T = Total Scaling Factor.
Display Units = The number of desired units (revolutions, feet, 10ths of
feet, meters, etc.) that would be acquired after the
“Number of Pulses” has occurred.
Number of Pulses = The Number of pulses required to achieve the number of
“Display Units”.
For the preceding example, the Total Scaling Factor, “K T ”, is calculated by
plugging in 2 and 48 in the formula:
K T = 2 ¸ 48 = 0.041667
As previously stated, the Total Scaling Factor, “K T ”, is the combination of the
Scale Factor, Scale Multiplier, and Number of Count edges. In many applications
the Total Scale Factor, “K
T ”, can be programmed directly into the Count Scale
Factor, “SF”, in which case the Scale Multiplier and Number of Count Edges can
be left at the factory settings of X1.
In some applications, more display resolution may be required. When the
Total Scaling Factor (K T ) is greater than 1.0000 and using only one edge per
count pulse, there may not be enough display resolution.
Example: With a Total Scaling Factor of 2.000, when an input pulse is
generated, the display will increment by 2. If the display units are in feet, when 3
feet have gone by, the display will still only read 2. It will not increment again
until 4 feet have been accumulated. With this amount of display resolution it
would be impossible to set the Preset and have the output respond at odd feet
intervals (1, 3, 5, etc.). To increase resolution, the Number of Count edges must
be increased. This can be achieved by selecting the CT+DIRX2 mode (Count
plus direction times 2) in the Program Count Module or by selecting the QUAD
X4 mode, if quadrature counting is being used. If enough resolution still has not
been attained, more input pulses will need to be generated per display unit.
The amount of resolution required will vary depending on the particular
application. In cut-to-length applications, a high amount of resolution is often
necessary. However, in totalizing applications, display resolution may not be
important. It should be noted that whenever the number of count edges is
increased to 2 or 4, the maximum count frequency will decrease. (See
Specifications for maximum count frequency).
Note: When using 2 or 4 edge counting for length sensor, on/off duty cycle must
be 50% to maintain max. accuracy (mag. pickup will not work).
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