Encoder Technical terms and explanations

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August 26, 2021

There are many and difficult technical terms used to define the technical data of an encoder. Below you will find a glossary that explains some of these terms.

Technical terms and explanations

Absolute encoderShaft encoder that transmits unique coded data for each increment
AccuracyThe difference between the actual and measured position
Alarm signalServes to monitor the shaft encoder for malfunctions, such as glass breakage, fouling, short circuit, short circuit of signal line, and supply voltage too low
Amplitude regulationCurrent or voltage amplitude is constant through regulation
Analogue signalA signal whose level alters continuously
ASICApplication specific integrated circuit
Axial loadMaximum load on the shaft encoder‘s shaft in the axial direction
BandwidthFrequency range for output signals
Baud rateRate of data transfer (bits per second)
BCDBinary-coded decimal; binary representation of a decimal number
BinaryTwo logical states (yes/no); the basis of binary data-processing systems
Binary codeCode using binary numbering; often udes for absolute measuring systems
Bit (Binary Digit)The smallest unit of information of a binary system. A bit can be 1 or 0 (yes-or-no decision)
Bus cycleTime needed for polling every bus slave by the bus master
ByteSequence of 8 Bits
CALCAN application layer
CANopenLayer 7 protocol based on CAN
CCW (Counter clockwise)Turning the encoder shaft in counterclockwise direction (in view of the shaft side of the encoder)
Change of stateFor CAN: Bus node (encoder) sends it‘s data automatically when position change occurs
ChannelSignal track on which 1 or 0 is outputted
Code switching frequencyNumber of position steps per second. For absolute shaft encoders with parallel interface: The maximum output frequency of the LSB output driver (fmax) also limits the maximum permissible code switching frequency:
Code switching frequency max. = 2 · fmax for Binary code
Code switching frequency max. = 4 · fmax for Gray code
Coefficient of thermal expansionMaterial expansion under influence of temperature change [µm/°K m], relevant for linear scales
ComplementaryOutput circuit for which also the inverted signals are outputted (e.g. Channel A and Channel -A). Electrically, the 1/0 levels are transmitted as voltage differences between two lines. In this way the information signal (the difference) remains pure as in general interferences are interspersed equally on both lines
CW (Clockwise)Turning the encoder shaft in clockwise direction (in view of the shaft side of the encoder)
Data busSystem of lines over which data are transferred electronically in parallel or serially
DCDirect current (not alternating)
EDS - fileElectronic data sheet. This is a file with the device specific parameter description and is provided by the manufacturer of a DeviceNet or CANopen device
EnableControl input via which the data outputs can be activated
Gray codeA special binary code that changes only one data bit per measuring step at a time. It is used with absolute encoders
Harmonic distortionMeasure for the signal quality of sinewave encoder [%]. It describes the content of
harmonics in analogue signals. The lower the number the better the signal
Incremental encoderMeasuring method in which the variable is formed by counting increments (measuring steps). Transmits an electrical signal (yes/no) for each increment, determined by the marked disc
IPAlso named protection class.
The enclosure class is designated according to DIN 40050 / EN 60529, by IP and a two-figure code number. 1st digit Degree of protection against ingress of solid bodies:
0 - no special protection
1 - solid bodies with dia. > 50 mm, no protection against intentional penetration
2 - solid bodies with dia. > 12 mm, warding off fingers etc.
3 - solid bodies with dia. > 2.5 mm, warding off tools, wires, etc. (thickness > 2.5 mm)
4 - solid bodies with dia. > 1 mm, warding off tools, wires, etc. (thickness > 1 mm)
5 - dust in harmful quantities, complete shock-hazard protection
6 - dust /dust-tight), complete shock-hazard protection
 
2nd digit Degree of protection against water:
0 - no special protection
1 - water dripping vertically
2 - water dripping at angles up to 15° from vertical
3 - water dripping at angles up to 60° from vertical (spraying water)
4 - water from all directions (splashing water)
5 - water from a nozzle from all directions (hose-water)
6 - heavy seas or strong jet of water (flooding)
7 - water, if the device is immersed in water under specified conditions of pressu- re and time (immersion)
8 - water, if the device is submerged constantly. The manufacturer must describe the conditions (submersion)
9K - acc. to DIN 40050 / Part 9: protected against high-pressure water/ steam jet cleaning
 
Example: IP65 A device thus designated is dust-tight, and protected against hose-water
Output circuitSee below
Open- Collector outputAn output circuit where the emitter of the output circuit transistor is the common and the collector is open
Voltage OutputAn output circuit where the emitter of the output circuit transistor is the common and a resistor is inserted between the collector and the power supply to convert the output from the collector to a voltage
Line-driver OutputAn output method that uses a special IC for high-speed, long-distance data transmission that complies with the RS-422A standard. The signal is output as a differential secondary signal, and thus is strong with respect to noise. A special IC called a line receiver is used to receive the signal output from a line driver
Complementary OutputAn output circuit with two output transistors (NPN and PNP) on the output. These two output transistors alternately turn ON and OFF depending on the high or low output signal. When using them, pull up to the positive power supply voltage level or pull down to 0 V. The complementary output allows flow-in or flow-out of the output current and thus the rising and falling speeds of signals are fast. This allows a long cable distance. They can be connected to open-collector input devices (NPN, PNP)
Pulse (repetition) frequency, max. speedThe maximum signal frequency achievable by the shaft encoder, the product of rotary and number or markings
Radial loadMaximum loading of shaft encoder shaft in radial direction
Reference pulseSquare-wave signal generated by a reference mark, usually only one increment wide, to provide an absolute reference for an incremental shaft encoder
RepeatabilityDegree of deviation for a point approached repeatedly under identical operating conditions
ResolutionNumber of increments/pulse counts per revolution (rotary) or distance between two increments (linear)
RS 422Standardized interface for undirectional point-to-point connections (for description refer to „Complementary“); voltage difference 7 V DC max
RS 422/485Interfaces for serial data transfer with specifications to EIA standards
RS 485Like RS 422, however as a bidirectional bus interface
SenseThe Sense lines (Sense VCC and Sense GND) enable measurement of the factual encoder voltage without adulteration by voltage drop due to supply current and cable resistivity. With that e.g. supply voltage can automatically be adjusted
SSISynchronous-serial Interface; standardized interface for serial data transfer
Starting TorqueThe torque needed to rotate the shaft of the Rotary Encoder at startup. The torque during normal rotation is normally lower than the starting torque. A shaft that has a waterproof seal has a higher starting torque

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