Digital IO Application Wiring Guide: Wiring Inputs
In this first installment of digital IO application wiring guides, I'll be covering three common use cases for interfacing with Vention's digital IO module input pins. Please leave a comment if you have a specific wiring application you'd like me to cover in an upcoming post!
Vention's digital IO module is equipped with 4x 24V digital inputs. The full electrical specifications for the digital IO module can be found here. In a nutshell, the digital inputs have pull-up resistors. They are "normally high", meaning if no sensor is connected, or if the sensor is not triggered, they will report a "logical 1" or a signal voltage of 24V.
Digital inputs can be used to sense and response to external signals, such as sensors, buttons and even other controllers, such as PLCs or microcontrollers. This application guide will cover interfacing with these three scenarios:
- Interfacing Vention input pins with sensors
- Interfacing Vention input pins with buttons
- Interfacing Vention input pins with 3rd party outputs
1. Interfacing Vention input pins with sensors
Sensors generally require 3 connections to be made in order to properly function. The 24V pin and ground pins are used to provide power to the internal electronics of the sensor, and then the 3rd pin changes voltage between 0 and 24V as the sensor toggles between active and inactive states.
When you purchase a Vention sensor, there will be 3 "pigtail" connections coming out of the end of the cable. These pigtails should be screwed into the black terminal block of your digital IO module, as shown below:
All of Vention's sensors follow the same color scheme: Blue connects to 0V, Brown connects to 24V and black connects to the "active" pin. Vention's sensors are "NPN", which means the sensor outputs a signal value of 0V when it is active.
For example, the Retroreflective sensor will output a signal of 0V whenever the light beam is broken. Since the digital IO module reports a signal of 24V normally, the digital IO module will properly detect this change in sensor signal and report it your applications software.
If your sensor is of the "PNP" type, then extra considerations need to be made. Consult your sensors data sheet to determine whether it is "PNP" or "NPN"
A "PNP" sensor will report a signal value of 24V when the sensor is active, however the Vention digital IO module will also report a value 24V if the sensor is inactive! If you wire a "PNP" sensor directly to the Vention digital IO module, then your application software will be unable to detect the difference between a sensors "active" and "inactive" states.
If you must use a PNP sensor, a relay can be installed between the sensor and the input pin. See example #3 for an example.
2. Interfacing Vention input pins with buttons
Another common use case is to interface the digital IO module with push buttons. When pressed, the push button should connect the digital IO modules input pin directly to the digital IO's ground (0V) terminal.
Please note that the 24V pin should never be connected directly to the 0V pin. If your digital IO module suddenly becomes unresponsive, or if you see a red LED illuminating the interior of the module, please reach out to the customer support team at +1 800-940-3617 for assistance.
3 Interfacing Vention input pins with 3rd party outputs
In some cases, a Vention system should act in response to some other controller's output. Robot controllers, PLCs and vision systems will sometimes have output pins that signify a certain event has occurred. For example, some computer vision units will use a set of digital outputs to signify whether a part has either passed or failed a visual inspection.
Generally, these 3rd party outputs have a separate power source than MachineMotion, so the 3rd party output cannot be directly wired into the digital IO inputs. Instead, it is recommended to use a relay in order to isolate the two systems from each other.
A relay can be thought of as a push button that is controlled by another circuit, rather than controlled by a human.
Just like the push button example, the relay should connect the input pin to the digital IO's ground. Next, the two wires coming from the relay should be connected to the PLC. Of these two wires, one should be connected to the PLC's output pin, and the other should be connected to either the PLCs ground pin. There should be no wires directly connecting the digital IO module to the PLCs output. The PLCs' documentation will likely give extra guidance on proper wiring into their output ports.
Post below with any additional wiring questions you may have, and please get in touch if you have application specific questions for you and your design.
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