Red Lion GEMINI 2 - Manual (Page 51)

4. Any calculated scale factor may be divided by a factor of 10, by programming
Function Code 61 (dummy right-hand zeros) to [61 1], which will display a
constant zero in the least significant digit.
(Note: This decreases the precision of the display from +/-1 digit to +/-10 digits.)
The same procedure may be accomplished for 100 and 1000 with [61 2] and
[61 3].
The use of one or more of the above capabilities will solve most applications
where the calculated scale factor value exceeds 5.9999.
There are two other considerations that should be discussed concerning
sample time and scale factor calculations.
1. Occasionally, the input pulse rate will greatly exceed the desired readout, and
this may result in a scale factor with only 1 or 2 significant digits programmed
into the Gemini. For example, assume a calculated scale factor of 0.003246.
Instead of programming 0.0032, the Function Code 45 (scale multiplier) is
programmed [45 3], which multiplies the input pulses by 0.01 and allows the
scale factor of 0.3246 to be used. This increases the precision by adding two
additional significant digits.
2. In applications where greater precision is desired, it may be necessary to use a
longer sample time. This will take a larger sample of incoming pulses, and will
in fact result in greater precision. (In most cases, the input pulses available will
allow for +/-1 digit precision even at the one-second sample time level.)
APPLICATION EXAMPLE [B]
The shaft of a positive displacement pump has a 14-tooth sprocket that is being
sensed by an LMPC0000. The unit is pumping 810 liters of water per minute when
the shaft is turning 400 RPM. The desired readout is in liters per minute (LPM).
CALCULATING PPS
RPM x PPR = PPS = 400 x 14 = 93.33 PPS
60 60
CALCULATING SCALE FACTOR AT 1-SECOND SAMPLE TIME
Desired Readout = Scale = 810 = 8.68
PPS x Sample Time Factor 93.33 x 1
In this application, the 5.9999 scale factor has been exceeded. To complete the
requirements, the calculated scale factor 8.68 is divided by 2, and the resultant
4.34 is loaded into the scale factor. Then the Function Code 44 (number of count
edges) is programmed [44 2], which doubles the input pulse rate, and causes the
Gemini to register the correct display at the 4.34 scale factor level.
APPLICATION EXAMPLE [C]
In this application, a photo-cell sensor is being used to count each bottle as it
moves along a bottling process. The requirement is to display bottles per minute
(BPM). There is no rotary motion that can be sensed to gain a greater input pulse
rate. Normal rate is 400 BPM.
The PPS formula does not fit this application. In this case, in order to calculate
PPS, the 400 BPM rate is simply divided by 60 seconds.
400 BPM = 6.66 PPS
60 seconds
First, the 6.66 PPS is factored into Formula (B), using a one-second sample
time.
Desired Readout = Scale = 400 = 60.06 Scale Factor
PPS x Sample Time Factor 6.66 x 1
The 60.06 is well above the 5.9999 capability, and the use of other Gemini
2000 capabilities will be necessary.
The magnitude of difference between the calculated scale factor and 5.9999
indicates that a sample time of 10 should be tried next.
60.06 = 10.01 - Sample Time 10 seconds
5.9999
Desired Readout = Scale = 400 = 6.0060
PPS x Sample Time Factor 6.66 x 10
This is just above the 5.9999 scale factor range; however, we can use Function
Code 44 to bring this scale factor value within the unit’s range. Simply divide
6.0060 by 2 and program 3.0030 into the scale factor. Then program Function
Code 44 (number of count edges) to [44 2] to double the input pulse rate. The
Gemini will now update every 10 seconds, and indicate the correct BPM rate.
This application demonstrates how the various Gemini capabilities can be
grouped together to solve a special rate indication application.
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