5-21
OPERATION
To minimize the scaling operation error, select such a scaling factor that permits the
largest possible number of digits to be contained in scaling display values (DSP).
The relationship between the scaling input and display values for input pulse
frequency is represented by the following equation.
Scaling display value = α (multiplication factor) × Input frequency (Hz)
Where α = DSP ÷ INP.
α is often an indivisible number such as α =5.654866... particularly when the input
value is converted to a circumferential velocity. This is because such a conversion
involves π.
There are innumerable combination of scaling input values (INP) and scaling display
value (DSP) that result in α =5.654866... as follows.
INP (Hz) DSP
1 5.654866...
2 11.30973...
5 28.27433...
10 56.54866...
...
On the other hand, DSPs that are programmable are limited to 5-digit integers.This
means that DSPs must be rounded off to the nearest integers as follows.
INP (Hz) Programmable DSP
1 00006
2 00011
5 00028
10 00057
...
Hence, if the input frequency is 1000 Hz, the error between the scaling result and the
ideal value increases with the decreasing number of digits contained in the DSP.
INP (Hz) Programmable DSP Scaling result Ideal value |Error|
(Readout)
1 00006 6000 5655 345
2 00011 5500 5655 155
5 00028 5600 5655 55
10 00057 5700 5655 45
..
Select a combination of the DSP and INP so that the scaling output contains the
largest possible number of digits. Doing so minimizes the scaling operation error.
How to Determine
Appropriate
Scaling Factor
5-13 Specifying the Scaling Factor (K3MA-F)
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