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Encoder Frequently Used Terms Ⅱ!

Changchun Rongde Optics Co.,Ltd.   Release time:2018-09-10   Browse:988

Bit: In incremental encoders a bit refers to 1 quantum of data or 1 increment of digital code. In absolute encoders a bit refers to the number of tracks which normally equate to the power of 2 of the final resolution, e.g., 8 bits equals 2 to the 8th power (256 positions), 12 bits equals 2 to the 12th power (4096 positions), etc.

Line Driver: A type of encoder output. This is the general term used for a differential output driver intended for use with a differential receiver. Line drivers can be used to source or sink current, have a low output impedance and, when used with a differential receiver, have a high noise immunity, even when used with particularly long cable runs.

Complement: The inverse of a digital signal. When a data channel transitions from the HI state to the LO state, it’s complement will transition from LO to HI. Complementary output signals, when used with a differential receiver can utilize common mode noise rejection (CMNR) to reduce noise susceptibility.

Natural Binary Code: A common absolute encoder output format, it is constructed so the code counts up using natural sequence of binary counting. Example, the counting goes 000, 001, 010, 011, 100, and so on. The drawbacks to using this code sequence is that at several count positions, the code will have transitions on multiple bits simultaneously. Because of the normal variations caused by gate delays, line impedances, and other factors, the actual transitions don't occur simultaneously. Reading data during one of these times could result in an erroneous reading. Control systems can overcome this issue by taking multiple readings.

Open Collector: A type of encoder output driver that utilizes an NPN transistor. Electrically it is a current sink and requires a pull-up resistor from the supply voltage to the signal high line. This resistor can be internal or external to the encoder.

Edge Detection: Also called quadrature detection. A technique used in incremental quadrature encoders whereby the controller counts the edge transitions on the encoder signals. Counting the transitions on a single channel doubles the resolution (two transitions for every cycle). Counting transitions on two channels in quadrature results in four times the base resolution.

Parallel Absolute Output: Each bit of the data word is output in parallel on a separate data line. For example, an 8-bit parallel output would have eight distinct data lines. Together these eight lines are capable of representing up to 256 unique positions. Resolution for absolute encoders is expressed in bits and counts, where each successive bit increases the resolution by a factor of two. 10 bits = 210 = 1,024 counts per revolution

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