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How To Detect Objects with a Do-more PLC
(VID-DM-0023)
- Learn how to connect any PNP or NPN proximity, photo electric or ultrasonic sensor and mechanical switches to a Do-more PLC for object sensing and detection. A Do-more H2-DM1E is used in this video, but is also applicable to the T1H-DM1x Terminator PLCs.
Detecting objects with a Do-more PLC is easy. In this video we'll use - and 3 proximity sensors, an Ultrasonic sensor and 3 different types of Photo sensors diffuse, retro-reflective and through beam to detect the presence of an object. Here's what it looks like on the test rack. Here are the three Inductive Proximity Sensors, the Ultrasonic sensor and the Through beam, diffuse and retro reflective photo-optic sensors. First we'll connect the proximity and ultrasonic sensors, then we'll swap those out with the photo sensors. The Do-more has a 4 slot base with AC Power Supply, the CPU and an 8 discrete input module. Two of the proximity sensors are intentionally NPN and the other prox. and the ultrasonic are PNP just so you can see how to connect the different sensor types to your controller. Since we have both types of sensors, we need to make sure the PLC input module can handle both NPN and PNP. This Do-more input module has two commons. That's perfect because we can simply connect one common to the positive voltage rail so the NPN sensors can pull the I/O terminal low when they activate, and we'll connect the other common to the negative rail so the PNP sensor can pull the I/O pin on the PLC up when it goes active. And that's all you really need to remember when you have an NPN sensor which sinks current, you need an input module that can source the current. When you have a PNP sensor that sources current, you need an Input module that can sink the current. And since this input module handles both we're in good shape. AutomationDirect's sensors have a diagram on the sensor or on the wire showing exactly how to wire the sensor. This little box is the sensors load - which is the PLC and for this sensor we see that the PLC provides or sources current from the positive rail to the input of this sensor. So we know without even looking at the part number, that this must be an NPN sensor to sink that sourced current to ground. So we connect the two NPN sensors to this block of I/O with the positive common and we connect the two PNP sensors to this block with a grounded common. Perfect. If we bring up the Do-more Designer software and connect to the PLC, we can instantly see the results in the dataview when I pass a metal object in front of the inductive proximity sensors, we see the result and when I wave my hand in front of the Ultrasonic we also see that result. Easy. Notice that even though the NPN sensors are pulling the input terminal low, and the PNP's are pulling it high, none of that matters here. All we see in the dataview is if the sensor is ACTIVE. Once the sensor is properly wired you don't worry about whether the signal is high or low. The optical sensors are exactly the same thing. We have a through beam, a diffuse and a retro reflective sensor, but all we really care about is: are they NPN or PNP? The through beam is NPN and the other two are PNP, so we connect the NPN sensor to the I/O block with the Positive common and the PNP sensors to the I/O block with the negative or grounded common. I replaced the other sensors with these so when we bring up the dataview we get the exact same result. Mechanical switches can be connected as either sinking or sourcing it doesn't matter. AC Proximity sensors can also be used for sinking or sourcing, just make sure you have an input card that can handle the AC voltage. If you have any questions, please don't hesitate to contact AutomationDirect's Free Award Winning Tech Support during regular business hours. They will be happy to help. Also, don't forget the forums. There are lots of folks there that love to share their years of experience. Just don't post any Tech Support Questions on the forums AutomationDirect's support staff doesn't monitor the forums on a regular basis.
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