Red Lion LEGEND - Manual (Page 68)

RATE SCALE MULTIPLIER
The general rule for choosing an SCM value is, when the Total Scaling, “K
T
”,
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. If the Total Scaling, “K
T
”, is greater than 5.9999,
then an SCM value of 10, 100, or 1000 can be used to obtain a Scale Factor Value
between 0.6 and 5.9999.
In our initial example, the Total Scaling, “K
T
” was determined to be 0.020833.
It is easy to see that this number cannot be programmed into the Scale Factor,
“SF”, without losing significant digits. Using formula #2 and the general rules
stated above, a Scale Multiplier Value of 0.01 is chosen and the Scale Factor is
calculated as shown below. This will provide the maximum amount of
conversion accuracy possible.
K
T
¸ SCM = 0.020833 ¸ 0.01 = 2.0833
In situations where the Total Scaling is already in range of the Scale Factor
(0.0001 to 5.9999) and when there are no significant digits that are lost, the Total
Scaling, “K
T
”, can be programmed directly into the Scale Factor Value and a
Scale Multiplier value of X1 (the factory set value) can be used.
Example: If the desired display units are in feet and there are 100 pulses per foot,
the Total Scaling, “K
T
”, would be 0.01.
K
T
= Display units
¸
number of pulses = 1
¸
100 = 0.01
Since the Total Scaling, “K
T
”, is exactly 0.01, it can be programmed into the Scale
Factor Value, “SF”, and the Scale Multiplier Value, “SCM”, can be left at its factory
setting of X1. After the Scale Factor and Scale Multiplier values are selected, all that
is necessary to complete the scaling is to choose the Rate Conversion Factor. The
Rate Conversion Factor (RCF) can be selected to provide indication in Rate per
Second (X1), Rate Per Minute (X60), or Rate per Hour (X3600).
There may be situations where there are many more pulses per display unit
than needed. In these situations the minimum SCM value (0.01) may not provide
enough significant digits in the Scale Factor. To achieve more significant digits,
the Rate Conversion Factor should be set to Rate per Second and the following
formula be used.
SF = K
T
x RCF ¸ SCM
WHERE:
RCF = 60 for display reading in Rate Per Minute or 3600 for display
reading in Rate Per Hour
RATE SCALING EXAMPLE:
EXAMPLE #1:
A 60-tooth gear is mounted to a roll that has a circumference of 2 feet. It is desired
to have a rate readout with a resolution in 10ths of feet per minute. Calculate the
Scale Factor and Scale Multiplier values necessary to provide the desired readout.
In this example one revolution of the web will provide 60 pulses for 2 feet of linear
travel. Since the desired display units are to be in tenths of feet, it is necessary to
convert 2 feet to tenths (2
¸ 0.1 = 20), giving us 20 tenths (display units). The Total
Scaling, “K
T
”, is calculated by simply plugging in the two numbers into Formula #1.
K
T
= Display Units
¸
Number of Pulses = 20
¸
60 = 0.333333
To get the maximum number of significant digits in the Scale Factor we use
formula #2 and a Scale Multiplier value of 0.1 as shown below.
SF = K
T
¸
SCM = 0.333333
¸
0.1 = 3.3333
To obtain rate indication in Feet Per Minute, the Rate Conversion Factor is
programmed for the Rate per Minute mode. A decimal point is programmed to
0.0, which allows the unit to display in 10ths of feet.
EXAMPLE #2:
The shaft of a positive displacement pump has a 14 tooth sprocket that is being
sensed by a magnetic pickup. It is known that the unit pumps 810 liters of water
per minute, when the shaft is turning 400 RPM. It is desired to have a display
readout in liters per minute.
With the Legend Plus, it is not necessary to deal with time unit conversions. From
the information given, we know that when the shaft has turned 400 revolutions, 810
liters of water will have been pumped. The first step we need to take is to calculate the
number of pulses that occur when 810 liters have been pumped.
Number of Pulses = # of Rev x Pulses per Rev
= 400 Rev x 14 PPR = 5600 pulses.
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