Scaling - AB Quality ALLEN-BRADLEY 1791 User Manual

Chapter 1
Introducing Block I/O

Scaling

1-6
This is illustrated using the +10V scale below:
Resolution
Input Signal
I1 I2
In the above scale, input signals 1 thru 5 produce corresponding internal
analog to digital converter (ADC) binary counts. A full scale (FS) voltage
input produces an internal count of 16383 (input signal 1), while a bottom
scale (BS) voltage input produces an internal count of 0000 (input 5).
During calibration, the module's representation of the counts are adjusted
so a voltage of nominal full scale (NFS) will produce a count shown as
input signal 2 while the nominal bottom scale voltage (NBS) produces a
count shown as input signal 4. For each range scale, the input voltage
which produces the ADC count of input signals 1 thru 5 in the above scale
are shown below:
Input Signal +/-10V
10.25V (FS)
I1
+10.000V (NFS)
I2
0.000V
I3
-10.000V (NBS)
I4
-10.25V (BS)
I5
The input data represented at the module is always the internal ADC binary
counts scaled by values set in the maximum (S
scaler value using a two point scaling method. The input voltage which
produces input signal 2 (V
signal 4 (V ) is equal to S
nbs
Smax
Scaling
Input Signal
I1 I2
Vnfs
Voltage
14 Bits
13.96 Bits
I3
Nominal Range
0-10V +/-5V
10.25V (FS) 5.125V (FS)
10.00V (NFS) 5.000V (NFS)
5.00V 0.000V
0.00V (NBS) -5.000V (NBS)
-0.25V (BS) -5.125V (BS)
) and minimum (S
max
) is always equal to S
nfs max
as shown below:
min
I3
I4 I5
0-5V
5.125V (FS)
5.000V (NFS)
2.500V
0.000V (NBS)
-0.125V (BS)
)
min
, and voltage of input
Smin
I4 I5
Vnbs