DESCRIPTION AND OPERATION
DIGITAL I/O
2 - 4
I-E96-316A
®
The QRS has two possible propagation (speed) choices for DC
inputs to allow for contact debounce time: a slow setting (17
millisecond response time) and a fast setting (1.5 millisecond
response time). Jumpers on the QRS select the voltage level
and response time for each input.
explains the
jumper connections.
Digital Inputs
Current limiters and optocouplers in the isolation block isolate
the three field inputs from the module circuitry. The threshold
detection block circuits test the input voltage to determine if it
is at the proper voltage level to indicate an energized (closed) or
de-energized (open) state for the field device. These values are
sent to the digital I/O buffer block. Jumpers on the QRS select
the threshold detection voltage level.
Digital Outputs
The output isolation block consists of optocouplers to isolate
the control logic circuits from the process. Four open collector
transistors that can sink a 250 mA load make up the driver
block.
Figure 2-3. IMQRS02 Digital Input and Output Circuits
TP27116A
DIGITAL OUTPUT
DIGITAL INPUT
FROM OUTPUT
CIRCUITRY
FIELD
OUTPUT
+5 V
–
+
+5 V
+5 V +5 V
+5 V
FIELD
INPUT
–
+
4
2
3
1
–
+
TO INPUT
CIRCUITRY
1
3
2
4
