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  • An encoder is a device that is used in many industries to provide feedback.

  • In the most basic terms, an encoder,

  • regardless of the type, which we will cover later,

  • senses position, direction, speed, or counts.

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  • Encoders will use motion, under a variety of technologies,

  • and translate it into an electrical signal.

  • That signal is then sent back to a controlling device,

  • such as a PLC, and is interpreted, meaning scaled,

  • to represent a value that will then be used within the program.

  • Some of the technologies involved in encoders aremagnetic”,

  • mechanical”, “resistive”, andoptical”.

  • Opticalis the most widely used encoder motion translating technology.

  • There are different types of encoders

  • such asabsoluteandincremental”.

  • We will describe those in greater detail in a future lesson.

  • But for now, an example of an incremental, optical type encoder

  • uses a beam of light that passes through a disk

  • that has opaque lines in a specific pattern,

  • somewhat like the spokes of a wheel.

  • On the other side of the disk is a photo sensing device

  • that will interpret the light, based on the pattern on the disk,

  • picture a shutter, blocking and unblocking the light.

  • The pulses of light are then converted to an electrical signal

  • to be sent back to the processor,

  • through the encoder's output.

  • Encoders have a wide range of uses

  • which includeclosed-loopapplications

  • such asservo or VFD control”, “measuring”, andcounts”.

  • Here are some examples of processes that may use an encoder.

  • For VFD control, you may be running a pump,

  • on a VFD, to fill a tank full of a liquid.

  • You are requesting a certain speed

  • and want to verify that the pumps VFD is at the requested speed.

  • Anencoderon the VFD may be used for feedback of speed.

  • Next, let's give an example for a “measuringprocess.

  • In this application, you will need to cut some aluminum product to a particular size.

  • You are passing a long roll, meaning hundreds of feet,

  • of the aluminum sheet through a cutting mechanism.

  • You need to determine the amount of aluminum fed,

  • so that you can cut the sheets to the proper size

  • that will be used in a separate manufacturing process.

  • An encoder, attached to the conveyor

  • and reading the material that is feeding through your cutting assembly,

  • will indicate the length of material that has been fed since the last cut.

  • That feedback can then be used to adjust the cutting blade

  • to sever the length required.

  • For an example ofcounts”, consider this process.

  • You have a conveyor line that has bottles running on a conveyor.

  • They are counted by a photo-eye sensor when entering the assembly.

  • They have a cap with an aluminum tamper-proof foil on top

  • that needs to adhere to the bottle.

  • Once the foil is sealed, the bottle will then move down the conveyor line

  • and verified that it exited the cap sealing assembly

  • via an exit photo-eye sensor.

  • Some of the requirements for this station are:

  • The same number of bottles that enter the assembly

  • must exit in a “predetermined time frame”.

  • The bottle must not remain in front of anentranceorexitsensor.

  • The bottle must not be exposed to the inductive sealer

  • longer than a predetermined amount of time.

  • You must make this assembly flexible enough

  • to handle many types of bottles

  • and entrance and exit sensor placement.

  • Consider a prescription bottle, easy right? No handles,

  • just a bottle that is a standard size.

  • Now consider an antifreeze bottle

  • with a somewhat small cap and a very large handle.

  • How in the world are you going to meet the requirements for the machine

  • and remain flexible? If you put a pill bottle in, yep, easy peasy right?

  • bottle in, seal, bottle out, no sensors blocked.

  • If any of the requirements fail,

  • bottle in, seal, tips over and isn't counted out,

  • machine halts and alerts an operator of a malfunction.

  • How about theantifreezebottle?

  • Bottle in, cap passes in front of an entrance sensor,

  • bottle counted, then the handle;

  • the system faults because it sees a blockage at the entrance.

  • How do you tell the machine that this is expected behavior?

  • An encoderof course, and a “selector switchfor a setup mode.

  • To set up, insert your product, in this case, the antifreeze bottle.

  • You make sure to feed cap first

  • and it must contain a foil.

  • Your program reads an entrance on the sensor

  • and recordsan encoder reading

  • as well as determines that this is a “capand records that fact.

  • Your program then reads another entrance

  • and determines that this is notcap

  • and must be some other acceptable part of the bottle, possibly a handle.

  • The single bottle continues down the line

  • where the exit sensor is triggered.

  • At that point,you again record the encoder value.

  • You now have an encoder count

  • that registered at the entrance and exit.

  • In the code, you subtract the entrance from the exit

  • and you have a bottlecount”.

  • You now know precisely how long it will take that bottle

  • to move through the system,

  • meeting themust enter and exit

  • in a predetermined timeframe, in this case, encoder counts.

  • You have also made the flexibility aspect of different types of bottles

  • as well as being able to place the entrance and exit sensors

  • any reasonable distance apart.

  • When back in run mode,

  • the code knows that there's a handle to ignore

  • when it comes into the process and doesn't fault the machine.

  • You register the encoder at each bottle entrance

  • and predetermine when the bottle must exit.

  • If the bottle doesn't exit the machine in a timely manner,

  • which is based on your projection

  • and the current encoder count, the machine faults.

  • This is a great use of an encoder that is fully configurable.

  • Count in, count out, subtract, done.

  • Don't miss the next lesson

  • where we are going to discuss incremental and absolute encoders.

  • Want to learn PLC programming in an easy to understand format

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An encoder is a device that is used in many industries to provide feedback.

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