Delta RMC101 - Manual (Page 587)

Quadrature with Analog Output 6.3
Transducer Interface Modules 6-43
6324.75
50598 8 Invalid scale Invalid
Therefore, in this example, a Scale of 25299 and a Prescale Divisor of 4 should be used. Notice
that this reduced the error in the scale factor.
3. Entering the Correct Scale Value
Now that the Prescale Divisor has been calculated, you must multiply the exact Scale value you
found in step one by this Prescale Divisor and round to the nearest integer. For example, if you
had a scale that came to 2949.12, then you would have selected a Prescale Divisor of 8.
Therefore your correct Scale parameter would be 2949.12 x 8 or 23592.96 rounded to 23593.
Therefore, your effective scale is 23593 / 8 = 2949.125, which is within 0.0002% of the exact
scale.
Note: If the Scale parameter value you calculate to enter is 32768, you must enter 0 instead.
This is required because the range of signed 16-bit number is 32768 to 32767. Therefore, 32768
is not a valid number. We chose 0 to represent this value instead.
Example 1:
A user with a 1024-line encoder wishes to have position units in tenths of a degree of rotation on
the encoder’s shaft. Therefore, the user has 4096 counts per revolution and wants to have 3600
position units over that distance. This gives us the following exact scale calculation:
Notice that the scale comes out to a whole number. This is an ideal situation, as there will be no
scaling error. This will be the case when encoders are used that have line counts that are powers
of two, such as 64, 256, 512, 1024, 2048, and 4096.
We choose a Prescale Divisor of 1 for the following two reasons:
• We have no choice. Any larger divisor, when multiplied by the Scale value, would overflow the
acceptable range for the Scale value.
• Whenever the Scale calculated in the first step comes out to an exact number, the larger
Prescale Divisors do not add any accuracy to the scale. For example, suppose this user wanted
position units of degrees. Therefore, the scale would be 360 x 32768 divided by 4096, which
comes exactly to 2880. Even if we used a divisor of 8, the scale value entered would be 2880 x 8,
which is 23040. The effective scale is 23040/8, which comes out to 2880.
Therefore, we use the following two values:
Scale = 28800
Prescale Divisor = 1
Example 2:
A user has a 200-line encoder mounted on shaft A. Shaft A is geared 1:15 with shaft B, which
does the work. Therefore, it is on shaft B that the user wishes to have position units measured in
1000ths of a revolution.
We know that the user has 1000 position units per revolution on shaft B. We need to find out how
many encoder counts there will be for one revolution of shaft B. There are 800 quadrature counts
per shaft A revolution. Because it will take fifteen turns on shaft A to turn shaft B once, there will