Rockwell Automation 1791-XXXX ANALOG BLOCK I/O - Manual (Page 16)

Introducing Block I/O
Chapter 1
1-9
Voltage Outputs - 1791ĆN4V2 and 1791ĆNDV
A simplified schematic of a +10V output channel is shown below.
2
Opto
Isolation
DAC
Precision
Operational
Amplifier
Digital
Output
V
OUTS
2
V
OUT
V
RET
+
-
Isolated Analog
Output Common
2
2
Note: Schematic does not show overvoltage protection circuits. 12501-I
Isolated Analog
Output Common
Isolated Analog
Output Common
The +10V output provides 14 bits of resolution and is capable of driving
loads as small as 1k ohm. The output sacrifices a small amount of the
resolution to provide a margin of 2.5% to allow for system or calibration
inaccuracies as shown below.
14 Bits
13.96 Bits
Nominal Range
Resolution
Margin Margin
10.25 10 0 -10 -10.25 Output Signal
Scaling
The digital data sent to the output is always scaled by the values set in the
maximum (S
max
) and minimum (S
min
) scaler values using a two point
scaling method. When digital data sent equals S
max
, the output produces
+10.000V and the digital data sent equals S
min
, the output produces
–10.000V. The following equations shows this relationship:
Vout = M x Module Data + B
where:
20V
(Smax – Smin)
10 x (Smax + Smin)
M =
B =
(Smax – Smin)