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ROC827 Instruction Manual
Issued Mar-06 Input/Output Modules 4-9
Figure 4-7. Analog Output Module Field Wiring
Note: All I/O modules are isolated on the field side. Be aware that you can
induce ground loops by tying commons from various modules together.
4.5 Discrete Input Modules
The eight-channel Discrete Input (DI) modules monitor the status of
relays, open collector/open drain type solid-state switches, and other two-
state devices. Discrete Inputs come from relays, switches, and other
devices, which generate an on/off, open/close, or high/low signal.
The DI module provides a source voltage for dry relay contacts or for an
open-collector solid-state switch.
The DI module’s LEDs light when each input is active.
Each DI channel can be software-configured to function as a momentary
or latched DI. A latched DI remains in the active state until reset. Other
parameters can invert the field signal and gather statistical information on
the number of transitions and the time accumulated in the on- or off-state.
Caution
The Discrete Input module operates with non-powered discrete devices,
such as “dry” relay contacts or isolated solid-state switches. Use of the DI
module with powered devices may cause improper operation or damage.
The DI module senses the current flow, which signals the ROC827
electronics that the relay contacts have closed. The opening of the contacts
interrupts the current flow and the DI module signals the ROC827
electronics that the relay contacts have opened. A ROC827 can read a DI a
maximum of 20 times per second (50 millisecond scan).
+
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I
+V
250
CONTROL
CURRENT LOOP
DOC0505A
CONTROL
CURRENT LOOP
CONTROL
CURRENT LOOP
CONTROL
CURRENT LOOP
+
-
CURRENT LOOP DEVICE 4-20mA
ROC800 POWERED
1-5 VOLT CONTROL DEVICE
Representative
Internal Circuit
Field Wiring