 Welcome to Absolute Optical Encoders. An Absolute Optical Encoder is an electromechanical device used to provide feedback signals for motion control applications. These feedback signals can give the following types of information about rotary or linear mechanisms. Direction of rotation, position, and velocity. An Absolute Optical Encoder contains a disk, which is connected to the shaft being measured. The disk is placed between light sources and sensors. As they rotate together, pulses of light from an emitter strike a sensor. Every time a slot on the disk is aligned between them, each pulse of light is converted to an electronic pulse by the signal conditioner. It is called an Absolute Encoder because it always measures the absolute position. This means that the actual position is indicated by whatever measurement is made at that particular moment. An Absolute Encoder with four tracks is shown. It represents four-bit binary numbers. Each track requires a separate set consisting of an LED and a phototransistor sensor. Each track produces a binary bit, so four-bit binary words are produced to indicate the position. By using four digits, the binary count of 000 through 1111, representing numbers 0 through 15, is possible. If each number represents a section of equal size, the encoder disk is divided into 16 22.5 degree sections. Pure Binary Wheel, an Absolute Encoder that uses pure binary numbers can present a problem. If all the bits do not change at exactly the same moment as the encoder crosses over from one section to the next, a false number may be detected for a brief moment. One example is when the count increments from 01112 to 1002. If the most significant bit changes earlier than the other three bits, the encoder's output will temporarily read 11112, which represents a 180-degree error of the encoder position. To avoid this problem, another binary number system, called the Gray Code, is used instead. Gray Code Wheel. The Gray Code uses only ones and zeros as the digits for each of the bits. This table shows a comparison between the standard binary system and the Gray Code. With standard binary numbers, it is common to have more than one digit change simultaneously. With Gray Code binary numbers, only one bit changes at a time. The advantage is that if a bit changes too soon or too late, the error is very brief. It is also insignificant because it is less than one degree and never indicates a zone more than one section away. If each number represents a section of equal size, a Gray Code wheel with four digits gives the encoder a resolution of only 22.5 degrees for each number. The resolution is determined by the following calculations. The 16 represents the number of different four-bit numbers that exist. Resolution equals 22.5. To provide better resolution, some Gray Code wheels have more than four tracks that represent more than four-bit words. Question 1 of 3. An absolute encoder with six tracks requires separate sets of light sources, LEDs, and sensors. B6. Question 2 of 3. More than one digit can change at a time when a code goes from one count to the next. 8. Standard Binary. Question 3 of 3. The resolution of a Gray Code number is B degrees if the section of a five track encoder rotates 360 degrees. B11.25. You have completed absolute optical encoders.