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Sensing the position of an object without touching it is the job of a
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proximity sensor. This machine's job is the test new parts. Each time the air
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cylinder goes down and back up again that's one complete cycle. If we could
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sense that operation then we could put that data into some software and we
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could start to monitor and analyze the machines effectiveness. We could start to
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calculate its OEE or overall equipment effectiveness. In this video workshop
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we'll show you how to wire this proximity sensor and get its data into a
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digital input and then put that into a software application to calculate that
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OEE. I could watch this stuff all day but let's head back to the workshop and get started.
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Now Before we jump right in let's start with the big picture.
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What's the signal path look like from a high level? This block diagram shows how
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we'll take a proximity sensor and convert its electrical signal to digital
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data suitable for use in any number of software and cloud applications. For this
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workshop I'll be using a SNAP PAC Learning Center. It's basically a SNAP
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PAC system with a controller, a rack, several i/o modules that we use for
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training here at opto 22. And this panel simulates some typical i/o signals like
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a meter, potentiometer, LEDs, and switches. The controller is running a control
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strategy that's loaded into its memory. I'll be using PAC control on this
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Windows laptop to configure the strategy and then download it to the controller.
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Now you can get your own Learning Center and free PAC Control software at
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workshop.opto22.com There's got to be more than a dozen different types of
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proximity or prox sensors; radar, lidar, inductive, optical, and Hall effect are
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just a small handful. For this workshop we're going to be using a Hall effect
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sensor which senses a magnetic field. This is a pneumatic ram like the
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one we saw on the machine. Air ports at either end push the shaft backwards and
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forwards. There's a magnet mounted on the end of the shaft inside the cylinder. We
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can see that by putting this paperclip on top as we move the shaft we can see
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the paper clip track the magnet inside up-and-down. We can sense that same
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magnetic field with this Hall effect prox sensor.
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Let's first power up the prox sensor on the bench and get the LED working in the
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end of it. Looking at the data sheet for the prox sensor we can see that it
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requires a voltage from 6 to 24 volts and it's DC at just a couple of
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milliamps. So let's use this 12 volt DC power supply here. First let's connect
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the ground wire and then the positive wire.
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Now let's actually attach the prox sensor to the air cylinder. Okay
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we've attached the sensor at the top of the cylinder so that we know whenever
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the machine cycle is complete and the shaft is at the top of the cylinder. We
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can see the LED is working. Every time the shaft hits the top of the cylinder
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the LED comes on. So we know our prox sensor is wired correctly. Now when it
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comes to wiring the digital input module we need to take a look at the prox
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sensor instructions. We need to know if we're wiring the sensor to the positive
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or negative rail of the power supply through the digital input module. If we
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take a look at the spec sheet for the sensor we can see that the circuit
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diagram shows that the load in, our case the digital input module, is wired into
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the negative or ground rail of the power supply. So let's grab a digital input
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module. Now these come available in 4 16 and 32 channels per module. I'll use this
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four channel version the SNAP-IDC5. Notice how the wiring diagram is on the
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back of the module it's also available on the datasheet on our website. So let's
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first wire the power supply common to the first channel input on the module.
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Screw that down tight.
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Now we're going to wire the prox sensor to terminal 2 which is the hot wire of the
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module.Let's screw that down tight. Now let's connect that wire from the digital
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input to the prox sensor. First of all I'm going to crimp the prox sensor side.
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Squeeze that down nice and tight. Now let's push the wire in from the digital
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input module and let's crimp that side down. Okay that's the wiring done. Okay
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next we snap the module into position 7 at the end of the rack. Now let's make
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sure that both the prox sensor LED and the module LED are both working as
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expected.
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Yep beautiful every time the shaft gets to the end of the cylinder both the prox
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sensor and the module LED both work as expected. Okay so that's the wiring end
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the module installation done. Let's move on to the laptop now and configure the
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sensor in the software. Here we are in PAC Control we've already got our I/O
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rack configured so now let's double click on the empty slot in position 7 to add
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our digital input module, a SNAP-IDC5.
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Double click on the first point of the module and open the point configuration
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dialog. Now we can give the prox sensor a tag name like 'test_cycle_complete'. This
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is where the prox sensor is given a meaningful name for all of your software
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applications or cloud services so make sure you choose your name accordingly.
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Now click on the debug button to download this configuration to your
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controller. Click 'yes' to save and 'yes' that you've
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made a change and the download process will start. Once it's done click 'run' to
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execute the new strategy. Now double-click the point name in this
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debug window and we can confirm that we've configured our prox sensor correctly by
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viewing the digital state in real time. See how the state changes every time I
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move the shaft back and forth. So at this point you can use PAC Control to monitor
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the time it takes the machine to test each part and perhaps sound an alarm if
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it goes outside of any limits. Or we could log the number of test cycles per
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minute to the controller. Using a tool like NODE-Red you can write the test
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cycles to a database either locally or in the cloud or we could send it to any
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number of cloud services like Microsoft Azure or IBM Watson where it could be
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monitored and analyzed for overall equipment effectiveness. For more
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information about OEE and to see the parts that we used in this workshop
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visit workshops.opto22.com. So there you go the electrical signal from the prox
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sensor has been converted to digital data and analyzed for any anomalies.
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Cheers mate!