Red Lion LEGEND - Manual (Page 65)

SCALING FOR COUNT INDICATION (Cont’d)
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 the Total
Scaling, “K
T
”, divided by the Number of Count edges used as shown in Formula #2:
FORMULA #2: K
R
= K
T
¸
NCE
WHERE:
K
R
= Remaining Scaling Factor.
K
T
= Total Scaling.
NCE = Number of Count Edges.
In our original example, the Total Scaling, “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 X1. The Total Scaling, “K
T
”,
therefore equals the Remaining Scaling Factor, “K R ”.
K R = 0.041667
¸
1 = 0.041667
If the remaining scaling is between 0.6000 and 5.9999, it can be programmed
directly into the Count Scale Factor value and the X1 factory setting for the
Count Scale Multiplier “SCM”, can be used.
COUNT SCALE MULTIPLIER
The general rule for choosing a SCM value is, when the Remaining Scaling
Factor, “K
R
”, is less than 0.6000, a SCM value of 0.1 or 0.01 can be used to get a
Count 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
WHERE:
SF = Count Scale Factor.
K
R
= Remaining Scaling Factor.
SCM = Count Scale Multiplier.
Following our continuing example, it is easy to see that the Remaining Scaling
Factor, “K
R
” (0.041667), cannot fit into the Count Scale Factor Value without
losing significant digits. Using the Formula above and a Scale Multiplier value of
0.01 allows us to get the maximum number of significant digits possible for the
Count Scale Factor value:
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. The number of “Display Units” displayed
after 62 pulses have been counted should be 1.
STEP 1 - Calculate the Total Scaling, “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 Count
Scale Factor. A value of 0.01 results in a Count Scale Factor Value of 1.6129.
FORMULA #3
SF = K R
¸
SCM = 0.016129
¸
0.01 = 1.6129
-63-