Open collector wiring without a resistor – Rockwell Automation 1756-LSC8XIB8I ControlLogix Low-speed Counter Module User Manual
Page 78
78
Rockwell Automation Publication 1756-UM536A-EN-P - April 2012
Appendix C
Alternate Wiring for Non-IEC Type 3 Sensors
Choose a Pull-up Resistor for
an Open Collector Sensor
To choose a pull-up resistor for an open collector sensor, use the module’s
nominal input current specifications in
and the transistor’s current rating
to calculate the voltage drop across the pull-up resistor when the transistor is Off
and On:
– Choose a pull-up resistor that provides a minimum of 10V at the
module terminals when the transistor is Off (input module is On).
– Choose a pull-up resistor that provides a maximum of 5V at the module
terminals when the transistor is On (input module is Off ).
shows examples of two pullup resistor values with various power supply
voltages and their actual measured values.
Open Collector Wiring
without a Resistor
If the off-state current of your open collector device complies with the module's
off-state current specification of <1.5 mA max, the device may be wired as shown
below. The module's input impedance will function as the pull-up resistor.
Table 9 - Pull-up Resistor Examples for Open Collector Sensors (actual measured values)
R_Pullup
(Ohms)
V_Supply
(Volts)
V_Terminals
(Volts)
V_R_Pullup
(Volts)
I_R_Pullup
(mA)
P_R_Pullup
(Watts)
499
12
10.1
1.9
3.8
0.00722
499
24
21.6
2.4
4.8
0.01152
499
30
27.5
2.5
5
0.0125
1000
12
9.2
(1)
(1) A 1000 ohm pull-up resistor is not recommended for 12V applications because it does not provide a minimum of 10V at the
terminals.
2.8
2.8
0.00784
1000
24
19.3
4.7
4.7
0.02209
1000
30
25.1
4.9
4.9
0.02401
1
3
5
7
0
1
9
2
1
1
1
4
1
3
1
6
1
5
1
8
1
7
1
0
2
9
1
2
2
1
2
4
2
3
2
6
2
5
2
8
2
7
2
0
3
9
2
2
3
1
3
4
3
3
3
6
3
5
3
GND-0
GND-1
GND-2
GND-3
CTR-GND-0
GND-4
GND-5
GND-6
GND-7
Not Used
CTR GND-1
CTR GND-2
CTR GND- 3
CTR GND-4
5
6
7
7
IN-0
IN-1
IN-2
IN-3
CTR-0
IN-4
IN-5
IN-6
IN-7
Not Used
Not Used
CTR GND-
CTR GND-
CTR GND-
CTR GND-
CTR-1
CTR-2
CTR-3
CTR-4
CTR-5
CTR-6
CTR-7
2
4
6
8
1756-LSC8XIB8I
12…24V DC
+
-