Red Lion GEMINI 42 - Manual (Page 63)

rules stated above, a Scale Multiplier Value of 0.01 is chosen and the Scale Factor
is calculated as shown below. This will provide maximum amount of conversion
accuracy possible. SF = K
T
/SCM
SF = 0.020833/SCM
SF = 0.020833/0.01 = 2.0833
In situations where the Total Scale Factor 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 Factor, “K
T
”, can be programmed directly into the Scale Factor
Value and a Scale Multiplier value of 1 (the factory set value) used. For example;
if the display units are in feet and there are 100 pulses per foot, the Total Scaling
Factor, “K
T
”, would be 0.01 ( K
T
= Display units/pulses per display units = 1 / 100
= 0.01). Since the Total Scaling Factor, “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, or programmed to, 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 can be selected to provide indication in Rate per Second,
Rate Per Minute, or Rate per Hour.
Note: 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 mode 1, Rate
per Second and the following formula be used.
SF = K
T
x CF
SCM
Where: CF = 60 for display reading in Rate Per Minute, or
CF = 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 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, giving us 20 tenths (display units). The
Total Scaling Factor, “K
T
”, is calculated by simply plugging in the two
numbers into formula #1.
K
T
= Display Units/Number of Pulses
K
T
= 20/60 = 0.333333
In order 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 SF = 0.333333/0.1 = 3.3333
To obtain rate indication in Feet Per Minute, the Rate Conversion Factor is
programmed for Rate per Minute mode. A decimal point is also added to provide
for a display of feet in 10ths.
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 when the unit is pumping 810 liters
of water per minute, the shaft is turning 400 RPM. It is desired to have a display
readout in liters per minute.
With the Gemini, 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 Revolutions x Pulses per Rev.
NUMBER OF PULSES = 400 Rev x 14 Pulses per Rev = 5600 pulses.
We now have all the information necessary to scale the rate. The Total Scaling
Factor, “K
T
”, is calculated using Formula #1 as shown below.
K
T
= Display Units/Number of Pulses
K
T
= 810/5600 = 0.144643
It is noticed that there are more significant digits in the Total Scale Factor,
“K
T
”, than there are available for the Scale Factor, “SF”. In order to acquire the
maximum amount of significant digits for the Scale Factor, Formula #2 is used
and a Scale Multiplier value of 0.1 is selected.
SF = K
T
/SCM
SF = 0.144643/0.1 = 1.4464
The Scale Factor, “SF”, then becomes 1.4464 (1.44643 rounded to 4 decimal
places). This provides the maximum amount of conversion accuracy possible.
The final step is to select a Rate Conversion Factor. The Rate Conversion
Factor is chosen to be Rate Per Minute as was required.
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