Red Lion GEMINI 33 - Manual (Page 44)

APPENDIX “E” - SCALING FOR COUNTING
The Gemini 3300 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 Gemini 3300 to scale or multiply the
input pulses by a scaling factor to achieve the proper display units (feet,
meters, gallons, widgets, etc.). There are three different function codes that
are used in scaling the input pulses to the desired reading. They are: the
“Scale Factor”, the “Scale Multiplier”, and the “Number of Count Edges”.
All three are factored together to provide the Total Scaling that is necessary.
The “Number of Count Edges” can be 1, 2 or 4 (Quad x4). In the Quadrature
x4, Inputs 1 & 2 Response mode, both the rising and falling edges of both
Inputs, 1 & 2, are counted. In this mode the “Number of Count Edges” is 4.
The first step in scaling the counter requires that the “Number of Pulses”
per “Display Unit” or “Display Units” be obtained. This may require a small
amount of deductive reasoning. For 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 units of display 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” will be 2. The “Number of Pulses” per
“Display Units” (2 feet) would naturally be 48.
Once 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:
DISPLAY UNITS - The number of 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
inserting 2 and 48 in the formula. K
T
= Display Units/Number of Pulses = 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 Scale Factor, “SF”, and the Scale Multiplier and Number of Count Edges
factory settings, of x1, would be used.
In some applications, more display resolution may be required. Whenever the
Total Scaling Factor is greater than 1.0000 and when utilizing only one edge per
count pulse, there may not be enough display resolution. For 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 has gone by, the
display will still only read 2. It will not increment again until 4 feet has 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 will have to be increased. This
can be achieved by programming Function Code 44 to mode 2, 2 edges, or
Function Code 43 to mode 6, Quad x4, 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 (Quad x4), the maximum count frequency will decrease.
(See Appendix “B” for maximum count frequency specification.)
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).
Once the Number of Count Edges (NCE) to be used has been determined, the
Remaining Scaling factor required, “K
R
”, can be calculated. This is simply the
Total Scaling Factor, “K
T
”, divided by the Number of Count edges.
FORMULA #2: K
R
= K
T
/NCE
WHERE: K
R
- Remaining Scaling required
In our original example, the Total Scaling Factor, “K
T
” was determined to
be 0.041667. Since this value is less than one, sufficient pulse information is
being generated, i.e., there is enough resolution for the units selected. The
Number of Count edges can be left at the factory set value of 1. The Total
-42-