Red Lion GEMINI 33 - Manual (Page 45)

Scaling Factor, “K
T
”, effectively becomes the Total Scaling Remaining,
“K
R
”. (K
R
= 0.041667/1 = 0.041667)
If the scaling remaining is between 0.6000 and 5.9999, it can be
programmed directly into the Scale Factor value and the x1 factory setting for
the Scale Multiplier, “SCM”, can be used.
The general rule for choosing a SCM value is, when the Remaining Scaling
Required, “K
R
”, is less than 0.6000, an SCM value of 0.1 or 0.01 can be used
to get a Scale Factor value between 0.6 and 5.9999 or to the point where the
maximum number of significant digits is obtained.
FORMULA #3: SF = K
R
/SCM
Following our continuing example, it is easy to see that the Scaling
Remaining, “K
R
” (0.041667), cannot fit into the Scale Factor Value without
losing significant digits. Using the Formula above and a Scale Multiplier
value of 0.01, will allow us to get the maximum number of significant digits
possible (SF = K
R
/SCM = 0.041667/0.01 = 4.1667).
COUNTER SCALING EXAMPLE:
EXAMPLE #1:
A flow sensor provides 62 pulses per gallon. Calculate the scaling required
to provide a display reading in gallons.
In this example the number of “Display Units” is the same as the desired
reading, since there are no decimal points involved.
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.
K
T
= Display Units/Number of Pulses (Formula #1)
K
T
= 1/62 = 0.016129
STEP 2 - In this application 62 pulses per gallon provides more than enough
resolution, so the “Number of Count Edges” is left set to the factory
configured value of 1. With a “NCE” value of 1, the remaining amount of
scaling necessary is still 0.016129
K
R
= K
T
/NCE (Formula #2)
K
R
= 0.016129/1 = 0.016129
STEP 3 - In order 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.
SF = K
R
/SCM (Formula #3)
SF = 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 hundredths of a foot.
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. (250 hundredths) 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
K
T
= 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. In order
to get higher resolution, Quadrature x4 Input Response Mode is selected. This
will provide four times more 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
K
R
= 2.5/4 = 0.625
At this point, it can be seen that the Remaining Scaling 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 into the Scale Factor,
“SF”.
SF = K
R
/SCM
SF = 0.6250/1 = 0.6250
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