What is Encoder?

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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.

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 are magnetic, mechanical, resistive, and optical.

Optical is the most widely used encoder motion translating technology. There are different types of encoders such as absolute and incremental. 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 include closed-loop applications such as servo or VFD control, measuring, and counts. 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. An encoder on the VFD may be used for feedback of speed.

This example is for a measuring process. 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 rolling/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.


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