Acceleration (Maximum)
Maximum acceleration is the maximum rate of shaft speed change which will not mechanically affect the rated performance of the encoder. It is typically expressed in radians per second squared (rads/sec²).

Accuracy
Accuracy is the precision to which the output electrical signals represent exact mechanical shaft position. (Accuracy is not to be confused with resolution.)

Axial Load
Axial load is the force applied to a shaft end surface directed along the axis of rotation.

Channel
A single channel equals one incremental output.

Complementary
Complementary is the term for two identical periodic signals where one signal is electrically inverted from the other.
Example of singlechannel electrically inverted.
Complementary signals are typically generated by inversion of the electrical output from a single channel.

Differential Line Driver
Output stage of the encoder which produces two “complementary” pulse trains per output channel. These complementary outputs can be transmitted through long cables with minimal loss of signal integrity. Electrical noise effects are reduced when the signals are compared by the “differential line receiver.” Receiver input impedance should be matched to the line driver output and the transmission line for best noise immunity.

Direction Sensing
Direction sensing is the technique for detecting the direction of angular or linear motion where the output levels are Logic 1 (high) for one direction of motion and Logic 0 (low) for the opposite direction of motion. This is typically done in the user’s control.

Dual Channel
A dual-channel encoder produces two incrementaloutputs. These two outputs are generally in quadrature (90° phase separation) relationship to each other. They are typically referred to as Channel A and Channel B.

Frequency Response
Frequency response for an incremental encoder is the maximum frequency of the output signal in Hertz.

Incremental Encoder
An incremental encoder is a device which provides a series of periodic signals due to mechanical motion. The number of successive cycles (signals) corresponds to the resolvable mechanical increments of motion.

Index (Marker)
The index is a separate output signal generated by a special track which produces a single pulse (or transition change) at a unique position on the disk.
The index is typically used to identify a center, home position, reset point, or zero reference.

Gated Index (Marker)
A gated index requires an internal electrical circuit which causes the index to correspond in a direct relationship to the A and/or B channel.

Multiplication
Multiplication is any technique to derive an output resolution greater than the base line count of the encoder. This can be internal or external.

Operating Frequency
Operating frequency is the speed (revolutions per minute) times the resolution (lines per turn) divided by 60.
Operating frequency =
(RPM x Resolution)/60

Phase
Phase is electrical degrees of dis-placement between two encoder outputs, typically 90° in quadrature encoders.

Position Error
Position error is the difference between the theoretically correct shaft position and its position as indicated by the encoder cycle count.

Quadrature
Quadrature is the term for two identical periodic signals when the phase displacement is nominally 90 electrical degrees.

Quadrature Error
Quadrature error is the phase error when the specified phase relationship between any two channels is nominally 90 electrical degrees.

Radial Load
Radial load is the force applied to the encoder shaft perpendicular to the axis of rotation. Note: It is important to note where the force is being applied along the shaft, due to the cantilever effect.

Radial Load (Maximum)
Maximum radial load is the maximum force which may be applied perpendicularly to the shaft axis at a specified point along the shaft without exceeding manufacturer’s specifications.

Resolution
Resolution is a term defining the available number of divisions per turn for rotary encoders or per inch (millimeter) for linear encoders.
Resolution is theoretically unrelated to accuracy. Resolution is typically specified in pulses per revolution, cycles per revolution, counts per revolution, lines per inch (millimeter), bits per turn, bits per inch (millimeter), etc.

RPG (Rotary Pulse Generator)
Rotary pulse generator is another term for incremental encoder.

Symmetry
Symmetry is the ratio of the ON time to the OFF time of the output signal for one channel. This ratio is optimally 50–50.

Tachometer (Digital)
Tachometer is a term for an incre-
mental encoder that is used to indicate
or control speed.

Torque (Running)
Running torque is the rotary force required to keep an encoder shaft turning. It is typically expressed in oz-in.

Torque (Starting or Breakaway)
Starting (breakaway) torque is the rotary force required to overcome friction and cause the encoder shaft to begin rotating.