DESCRIPTION AND OPERATION
ANALOG I/O
2 - 2
I-E96-316A
®
ANALOG I/O
The QRS can input four separate analog signals (1 to 5 VDC),
and output two separate analog signals (1 to 5 VDC, 4 to 20
mA). The module accepts analog inputs that are either single
ended or differential voltages. It allows for a common mode
(inputs change together proportionally) differential voltage of
±
10 VDC. The QRS output mode is selectable: current or volt-
age. Figure
shows the analog input and output circuits.
Analog Inputs
The input conditioning block consists of two pole input filters
that reduce input signal noise. They provide 37 db of normal
mode rejection (differential change) and 53 db of common
mode rejection for the differential inputs.
The QRS uses analog voltage inputs only. Its respective Termi-
nation Unit (TU) or Termination Module (TM) is configurable for
current or voltage inputs; resistors on the TU/TM convert ana-
log current inputs to voltages that are sent to the QRS.
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.
Figure 2-2. IMQRS02 Analog Input and Output Circuit
TP27117A
ANALOG OUTPUT
BIAS
VOLTAGE
FROM D/A
CONVERTER
FIELD
OUTPUT
S3
FEEDBACK
+
–
+
–
–
+
–15 V
+24 V
–
+
ANALOG INPUT
TO A/D
CONVERTER
FIELD
INPUT
+
–
–
+
