DESCRIPTION AND OPERATION
ANALOG I/O
2 - 2
WBPEEUI240755B0
®
ANALOG I/O
The CIS and QRS modules can input four separate analog sig-
nals configurable as voltage (one to five VDC) single ended or
differential, or current (four to 20 milliamperes) field powered.
It allows for a common mode (inputs change together propor-
tionally) differential voltage of ±10 VDC. The I/O module out-
put mode is selectable: current or voltage.
Analog Inputs
The input conditioning block consists of two pole input filters
that reduce input signal noise (Fig.
). Refer to Table
for
normal mode rejection (differential change) and common mode
rejection specifications for the differential inputs. The input
conditioning block consists of an I/E conversion resistor and a
configuration jumper (for each channel) to configure the I/O
module to input current or voltage (single ended or differen-
tial).
The input select block consists of an analog multiplexer and
an inverting difference amplifier. The multiplexer selects one of
the four inputs or the reference block inputs (calibration volt-
ages). The difference amplifier converts the selected input to a
single ended signal.
The A/D converter block circuit changes the input signal to a
12-bit value that is sent to the I/O expander bus interface.
This value is an analog count that corresponds to the input
voltage. Nominal input range is 1 to 5 VDC (4 to 20 milliamps);
however, it allows for a 0.75 to 5.25 VDC (3 to 21 milliamp)
input range which is
±
6.25 percent of the nominal input range
span (4 VDC).
Figure 2-2. Analog Input Circuit Example
FIELD
INPUT
J17
1
2
3
4
T00325A
TO INPUT
SELECT
BLOCK
