Inputs - AB Quality ALLEN-BRADLEY 1791 User Manual

Chapter 1
Introducing Block I/O

Inputs

Simplified Schematic
Channel 0 Input
inV0
inI0
249Ω
RET in0
GND in0
1-4
Discrete transfer (Figure 1.3) is intended to be used with controllers which
do not have block transfer capability. However, discrete transfer can be
used with any PLC family controller. When using discrete transfer, the
block looks like a 1/2 I/O rack to the controller (four words of input image
table memory and four words of output image table memory). Note that
certain alarms and user scaling features are not available when using
discrete transfer.
Figure 1.3
Block I/O Connection in an SLC System using discrete transfer
1747 SN Remote I/O
Scanner Module
Blocks are daisy chained to
a scanner
A simplified schematic of the input circuit of one input channel is
shown below.
20MΩ
20MΩ
ATTENTION: The 249 ohm
input current shunt is rated at
0.25 Watts. Do not exceed this
power rating or apply more
Analog Input
1
than 6V across the resistor
Common
Inputs have selectable input ranges as shown below.
Application
voltage
voltage or current
voltage
voltage or current
1/2
Analog Multiplexer
Channel 0
Channel 1
Channel 2
Channel 3
Input Range Resolution
+10V 14 Bits
+5V 14 Bits
0 to 10V 14 Bits
0 to 5V 14 Bits
Block I/O each block
is 1/2 I/O rack
1/2
+
= 1 I/O Rack
Instrumentation
Amplifier
+
-
Analog Input
1
Common
10828 I
A/D
12501-I