Download 1771-2.69, Allen-Bradley Wire Fault 15

Product Data
Wire Fault (1527V DC)
Input Module
AllenBradley
Wire Fault 1527V DC Input Module
(Cat. No. 1771-DW)
Product Data
Description
The Wire Fault (15-27V DC) Input Module converts seven on/off DC
inputs to logic level signals compatible with Allen-Bradley programmable
controllers that use the 1771 I/O structure. The module also detects if any
wire in the circuit connecting the input device to the module or to the
power supply has either:
short circuited to ground
open circuited
You must connect a shunt resistor across the terminals of the input device
to allow the module to monitor the wire condition for a fault. Seven shunt
resistors, one for each input, are supplied with your module.
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Product Data
Wire Fault (1527V DC)
Input Module
Input Devices
Typical 2-wire (hard contact) input devices compatible with the module
include:
DC pushbutton, limit, float, and selector switches
The off-state leakage current of your 2-wire input devices should not
exceed 1mA.
Input Indicators
Seven status indicators are located on the front of the module. These
indicators show the status of inputs or the presence of a wire fault (figure
1). The indicator is on when contacts are closed, off when contacts are
open, or flashing when the module detects that a wire in the input circuit
has faulted.
Input Indicators
Figure 1
Wire Fault Status Indicators
Reset Switch
2
A pushbutton reset switch is located below the last input indicator. Use the
switch to manually reset the module after you have corrected a wire fault
detected by the module. Press the switch using a narrow object such as a
ball point pen.
Product Data
Wire Fault (1527V DC)
Input Module
Module Operation
You program the module to report contact status or wire status. The
sequences for monitoring and reporting contact status (figure 2, upper
path) or wire status (figure 2 lower path) are described as follows.
Figure 2
Wire Fault Module Block Diagram
Module alternately monitors contact status:
Contacts close.
Opto-electrical isolator protects logic signals by isolating logic circuits
from input wiring.
Input filter removes false signals due to contact bounce or electrical
interference.
Input indicator turns on or off to show status of input contacts.
Logic circuits process and store signals representing contact status.
Module alternately monitors wire status:
Input wire faults.
Opto-electrical isolator protects logic signals by isolating logic circuits
from input wiring.
Module detects short circuited or open circuited wire by detecting a
change in line monitoring current.
Module latches faulted wire condition, if one exists.
Module flashes the indicator for that input.
Logic circuits process and store signals representing wire status.
Module reports contact or wire status:
Module detects that your program set or reset the request bit.
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Product Data
Wire Fault (1527V DC)
Input Module
Module reports corresponding contact or wire status to I/O adapter (if a
remote I/O system) or to PC processor.
PC processor and/or I/O scanner (if a remote I/O system) read(s)
corresponding contact or wire status and returned status bit into the
processor data table.
After corrective action is taken for a wire fault condition, your program
(or reset switch) resets the latched condition in the module.
Line Monitoring
The module provides a 6mA monitoring current through the shunt resistor
for each input wire when input contacts are open, and a 20mA current
when contacts are closed and the input wiring is good. A shorted or opened
circuit disrupts this current.
Programming
You program the wire fault module similar to standard discrete I/O
modules with the following exceptions. (Block transfer is not used.)
Contact/Line Status — Your module constantly monitors contact and
wire status. Your ladder program selects which status is reads. We
recommend that you toggle the request bit to alternately read contact or
wire status, and use appropriate logic when your program detects a wire
fault.
Request Bit — The request bit tells the module to report either contact
status (bit is set) or wire status (bit is reset). The request bit is bit 07 or 17
of the module’s output image table byte depending on whether the module
is in the left slot (bit 07) or the right slot (bit 17) of the module group.
When your ladder program sets the request bit, the module’s input image
table byte reports contact status of the seven inputs. When your ladder
program resets the request bit, the module’s input image table reports wire
status of the seven inputs. The module is unable to determine if the wire
fault is a short or open circuit.
Status Bit — The status bit identifies whether the module is reporting
contact status or wire status. The status bit confirms the function dictated
by the request bit. The status bit is bit 07 or 17 of the module’s input image
table byte depending on whether the module is in the left slot (bit 07) or in
the right slot (bit 17) of the module group.
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When Data Table
Bits Are
I/O Data Indicates
Contacts Are
Status Data Indicates
Wires Are
Set
Reset
Closed
Open
Faulted
Good
Product Data
Wire Fault (1527V DC)
Input Module
For example, the module’s input image table byte for contact status (inputs
10 and 12 closed) and wire status (wires to inputs 11 and 15 faulted) would
appear as follows:
Bit Designation
07
06
05
04
03
02
01
00
17
16
15
14
13
12
11
10
Contact Status
1
0
0
0
0
1
0
1
Wire Status
0
0
1
0
0
0
1
0
Function
status bit
Data is contact status or wire status depending on status bit 07 or 17.
If all bits of the wire status byte are set, then the power supply could have
failed, or the field wiring arm could have been removed from the wire fault
module.
Module Reset — You must correct the cause after the 1771-DW module
detects a wire fault. Moreover, bits in the input image table remain set until
they are reset manually or by program reset.
Manual reset
Press the reset switch on the front panel
Program reset Reset bit 00 or 10 (depending on module location)
of the module’s output image table byte using
program logic
Use either method for resetting one or more wire faults that the module has
detected, and for resetting the module at power-up.
If you want to disable the pushbutton reset switch, change a configuration
plug inside the module. Do this by removing covers, locating the (blue)
configuration plug on the component side of the board behind the LED
indicator assembly, and floating the plug on one pin.
WARNING: Do not use the complementary address of this
module for word manipulation, or any I/O module as the
complement to this module. The reset bit (00 or 10) must be
reserved for the reset function. If you use the complementary
word address for an I/O module or for word manipulation,
unpredictable operation could occur with possible damage to
equipment and/or injury to personnel.
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Product Data
Wire Fault (1527V DC)
Input Module
Example Program — Examples of user program logic (figure 3) show
methods for storing contact status and wire status, resetting the module,
and conditioning the use of contact status according to the status of the
input wires.
The example program toggles the request bit on alternate scans so that the
module constantly updates contact status and wire status. The program
stores contact status and wire status in separate storage words. In this
example, it stores contact status in word 250 and wire status in word 251.
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Product Data
Wire Fault (1527V DC)
Input Module
Figure 3
Example Programming
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Product Data
Wire Fault (1527V DC)
Input Module
Input Connections
Connect your 2-wire input devices to the 1771-WA field wiring arm
terminals 0 thru 6. Terminal 7 is not used. Connect the positive output from
the power supply to each input device the negative output to the module’s
DC common terminal, terminal B. Connect the appropriate shunt resistor
across the terminals of each input device that the module monitors for a
wire fault. All unused inputs must have a shunt resistor in line with the
power supply’s positive terminal. Otherwise, the module reports a wire
fault for an input not connected (figure 4).
Figure 4
Input Connections
Power Supply
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You should maintain a constant input voltage between each of the module’s
input terminals (0 thru 6) and common terminal (terminal B). Select a
power supply voltage that produces 15V DC up to 27V DC between the
input and common terminals of the module. Allow for a voltage drop in the
wires to your input devices, especially if you choose a voltage at either end
of this range. We recommend a nominal supply voltage of 24V DC. Using
a power supply voltage other than 24V DC "5% will require that you
select a different shunt resistor and provide your own for each input.
Product Data
Wire Fault (1527V DC)
Input Module
Shunt Resistor
Use the 3.3k carbon film 1/2-watt resistors supplied with your module as
shunt resistors if your power supply voltage is 24V DC. Connect a shunt
resistor across the terminals of each input device that you want to monitor
for a wire fault.
WARNING: Connect the shunt resistor across the terminals of
the input device, or as close to the input could be intermittent or
not function. This situation could possibly cause damage to
equipment and/or injury to personnel.
If the power supply voltage is lower than 23V DC or greater than 25V DC,
use a different shunt resistor. Select the value of the shunt resistor based on
power supply voltage as follows:
Power Supply
Shunt Resistor
15V DC
18V DC
21V DC
24V DC
28V DC
1.8k ohms
2.2k ohms
2.7k ohms
3.3k ohms
3.9k ohms
Use shunt resistors having a "5% tolerance.
If your power supply voltage is other than those listed, calculate the value
of the shunt resistor as follows:
R = Power Supply Voltage – 800
0.006
Wire Resistance
The wire resistance is the total resistance in the wires (figure 4) between:
positive power supply terminal and input device
input device and input terminal on the module
module common and negative power supply terminal
Calculate your wire resistance by multiplying the total length of wire in
feet by the resistance per foot for the following wire sizes.
Wire Size
Ohms per Foot
10
12
14
16
18
0.000999
0.001588
0.002525
0.004016
0.006385
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Product Data
Wire Fault (1527V DC)
Input Module
Your wire fault module operates correctly if the wire resistance is less than
the maximum allowable value. The maximum allowable wire resistance
depends on the power supply voltage as follows:
Power Supply
Maximum Wire
Resistance
15V DC
18V DC
21V DC
24V DC
28V DC
25 ohms
50 ohms
75 ohms
100 ohms
133 ohms
WARNING: Your wire fault module will not operate correctly
if the resistance in the wires to each input device exceeds the
maximum allowable value. Intermittent operation could occur
with possible damage to equipment and/or injury to personnel.
If the resistance in the wires to each input device exceeds the maximum
allowable value for a power supply voltage, either use a heavier gage wire
(lower wire size), or raise the power supply voltage.
Input Filtering and
Circuit Protection
Input filtering limits the effect of voltage transients caused by contact
bounce and/or radiated electrical noise. If not filtered, voltage transients
could produce false data. The delay due to input filtering is nominally
33"6ms for turning inputs on or off, or 3"2 ms for detecting a wire fault.
Module logic and wire fault monitoring circuits are protected from
possible damage due to electrical transients by 1500V opto-electrical
isolation. The module’s inputs are protected from the application of reverse
voltage up to 250V DC.
CAUTION: Application of voltages above the maximum
specified input voltage can damage module circuitry.
Keying
The module is keyed to guard against installation in the wrong module slot.
To implement this protection, insert keying bands supplied with the I/O
chassis into the upper backplane connector of the slot for this module in
the following positions (figure 5):
Between 2 and 4
Between 20 and 22
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Product Data
Wire Fault (1527V DC)
Input Module
Figure 5
Keying Bands Placement
You can change the positions of keying bands if subsequent system design
requires the insertion of a different type of I/O module in this slot.
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Product Data
Wire Fault (1527V DC)
Input Module
Specifications
Inputs
G 7
OptoElectrical Isolation
(contact and line monitoring inputs)
G 1500V DC
Module Location inputs)
G 1771 I/O chassis
Backplane Current
G 300mA max
Input Voltage Range
G 15 to 27V DC
Environmental Conditions
G Operating Temperature
0 to 60°C (32 to 1 40°F)
G Storage Temperature
-40 to 85°C (40 to 185° F)
G Relative Humidity
Nominal Input Current
(closed contacts)
G 20mA @ 24V DC typical
Maximum OffState Current
(@ 24V DC)
G 1mA
5 to 95%
(without condensation)
Wiring
Nominal Line Monitoring Current
(@ 24V DC)
G 6mA contacts open
G 20mA contacts closed
G Less than 4mA for detection of
wire fault
G 14 gauge stranded (max)
G 3/64 inch insulation (max)
Keying
G Between 2 and 4
G Between 20 and 22
Input Impedance
G 1k2k ohms (on state)
G 2k3k ohms (off state)
Input Signal Delay
G 33"6ms for contact status
G 3 " 2ms for wire fault status
1985 Allen-Bradley Company.
PLC is a registered trademark of Allen-Bradley Company.
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Publication 1771-2.69 — February 1986
Supersedes Publication 1771-2.69 — February 1985
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