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Things to know about encoders
Guide for Rotary Encoders
Rotary Encoders
Rotary Encoders with analog or incremental interfaces in single or multiturn versions
Encoders are sensors that use electronics to record angle information in an application and convert it into electrical signals. Optoelectronic and modern technologies based on Hall effect sensors deliver excellent measurement results. In addition, the service life of the sensors is particularly long thanks to the contactless measuring principle. Thanks to the large selection of electrical signal outputs, connections and encoder designs, numerous variants are available for your application.
A key feature is the angle range that the encoder can detect. Angles up to 360 degrees are covered with single-turn encoders, and angles above with multiturn encoders. A distinction must also be made between absolute value output and incremental output. In addition, when choosing the correct product, it is important to pay attention to environmental influences and easy servicing.
Among all the possible parameters, each sensor technology has its own advantages and each sensor has its specific properties, which we would be happy to work out together with your application requirements as part of our advice. In demanding applications, technical product adaptations are often required. MEGATRON is your specialist for these cases and offers the best solutions technically and economically. We support you from the inquiry, through the implementation of the series to the "end of life" of your application with high delivery reliability and assured quality products as a long-term, reliable partner.
Index
What is a rotary encoder?
Encoders detect or specify angular positions/positions and convert this information into electrical signals. They are angle sensors that transmit their measured value to an electronic system without contact. And it is precisely this characteristic that distinguishes them from potentiometers, which are passive components. Basically, each encoder consists of a housing, an electronics with sensor as the heart of the measurement and the electrical connection. Depending on the version, a shaft with a shaft bearing is also part of the sensor in order to produce the angle measurement mechanically. There are numerous related terms for the word encoder. However, if the angle is provided as a complete value (i.e. as an absolute value) with a fixed reference to a zero position, then the rotary encoder is referred to as an absolute encoder. If only the change in angle is provided, i.e. the output signal only provides relative information, then the encoder is an incremental encoder. In this guide, only contactless technologies with magnetic or optical measuring principle are described.
What does "contactless" mean?
Contactless means that the measured value is transmitted to the electronics without contact. For example, a rotating part of the application is connected to the encoder's shaft, and the measured value is recorded by the electronics. However, there is no direct mechanical connection between the two components. Thus, the measured value is therefore transmitted without contact.
All contactless encoders from MEGATRON are based either on magnetism or on an optical measuring principle. With magnetic encoders there is practically no wear on the acquisition (electronics) and with optical encoders only the optical detection unit has a limited lifespan. The only noteworthy wear occurs in contactless encoders via its mechanical components for recording measured values when there is a shaft and shaft bearing.
Magnetic rotary encoder with Hall effect
The Hall effect, named after Edwin Hall, describes the occurrence of an electrical voltage, the so-called Hall voltage, in a current-carrying conductor (Hall element) that is located in a stationary magnetic field. If you place a circular diametrically magnetized (north pole / south pole) permanent magnet over a Hall element, expose this magnet to a rotary movement and measure the voltage at the output of the amplifier circuit, then a sinusoidal output voltage curve is measured.
In principle, external magnetic fields can interfere with this technology. So-called gradient-based Hall sensors are mainly used, which are largely insensitive to these disturbances.
For more details, see our guide on the topic of "absolute encoders".
For further details, see our guide to absolute encoders.
| Advantages of magnetic encoders | Disadvantages of magnetic encoders |
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Optical encoders
Optical encoders are based on a contactless, optical scanning principle. Light is generated by a light-emitting diode that shines through a coding wheel onto a photodetector. The photodetector generates an electrical signal that is processed by the electronics and used to output the measured value.
In non-contact rotary encoders with optical scanning systems, the light-emitting diodes are subject to a continuous ageing process during operation. In addition, dust on the optical system contribute to the ageing of the sensor.
For more details, see our guide to incremental encoders.
Coding wheel
The overview of all incremental encoders with optical sensor technology can be found here
| Advantages of optical encoders | Disadvantages of optical encoders |
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Incremental encoders
Incremental encoders output a certain number of rectangular signals instead of information proportional to the angle (cf. absolute encoders). They are also referred to as pulses. Incremental encoders are therefore also called rotary pulse encoders and the number of pulses per revolution is always given (unit imp./rev.). One pulse corresponds to one period duration. The term "one increment" is also used for a period duration. This also explains the term incremental encoder. An external evaluation unit is always required to evaluate the measurement result of an incremental encoder, for example a counter.
Signal sequence incremental encoder
The following points are to be observed in particular:
- For an angle measurement, the number of pulses must be counted in an external evaluation unit and the sum of the pulses must be converted into an angle.
- If the operating voltage of the counter is interrupted, the counter information is usually lost. If then the absolute value of the angle relative to a reference point is to be measured or calculated, referencing must be carried out by passing through the zero position.
- For a speed measurement, the number of pulses per time is calculated.
Incremental encoders are available with different numbers of pulses per revolution. If, for example, there are 360 pulses/rev, this means that 360 pulses (360 signal periods) are output per full shaft revolution (360°). If, for example, 1024 pulses/revolution are specified, this means that 1024 pulses (1024 signal periods) are output per full shaft revolution (360°).
Incremental encoders are available from MEGATRON as Hall encoders and as optical encoders. For a detailed description, see the Incremental Encoder Guide.
Absolute encoders
Absolute encoders output an analogue or digital signal proportional to the angle. There is therefore a fixed reference point for the angle measurement. Rotary encoders with analogue output provide the measured angle as output voltage, output current or pulse width (PWM). Digital interfaces for the output of absolute values are available in the form of communication protocols.
For a detailed description, see the Absolute Encoder Guide.
Analogue output signal of a singleturn absolute encoder
| Measured angle [°, degrees] | Output voltage [Volt] |
| 0° | 0 V |
| 360° | 10 V |
| 45° | 1.25 V |
| 90° | 2.5 V |
| 180° | 5 V |
| 360° | 10V |
The table shows the output voltage curve at different measurement angles using the example of a 0...10 V voltage output
Single- vs. Multiturn encoders
Singleturn encoders
Singleturn encoders are absolute encoders that can only measure the angle of one full revolution. After one full revolution, the output signal shows the same value every 360° as for 0°. Most contactless singleturn absolute encoders measure the full angle range from 0° to a maximum of 360°. Only a few products measure angles in a limited angular range, for example +/- 45°.
Multiturn encoders
True-Power-On absolute encoder HSM22M
Compared to single-turn encoders, multiturn encoders are able to measure angles beyond 360° The measuring system is able to count the number of revolutions, and it is usually programmed so that the signal rises continuously over the maximum electrically effective angular range. For example, certain multiturn absolute encoders from MEGATRON are able to measure angles up to a maximum of 72000° (up to 200 shaft revolutions). The overview of all multiturn encoders can be found here.
Without special precautions, such encoders lose their position information if the supply voltage is interrupted. One class of multiturn encoders are true power-on encoders. Such an encoder also delivers a correct output signal if the angle of rotation changes as desired during a temporary absence of voltage.
Actual value device and setpoint device
The two terms "actual value device" and "setpoint device" are defined by their purpose in the application. Some encoder models can be used for both purposes.
For a setpoint device, a value is set manually. A setpoint is specified via a manual rotation of the encoder shaft (usually via an adjustment button mounted on the shaft). These adjusters / manual adjusters are used in control panels, for example to navigate through menus or to specify various parameters for measuring devices. The overview of devices for manual input can be found here.
The actual value encoder is used as a synonym for an angle sensor or rotary encoder if an angle is simply measured and is not specified manually by hand. Since this does not necessarily correspond to the target value in an application, the two terms are used to differentiate. Setpoint and actual value transmitters can be parts of control loops.
MRX50 rotary encoder as setpoint devices
Angular properties and direction of rotation
Mechanical angle of rotation
The mechanical angle of rotation is the entire angle at which the encoder can be operated mechanically. The mechanical angle of rotation is not mechanically limited for most contactless encoders, i.e. the shaft of the encoder can be operated clockwise and counterclockwise continuously without stopping the rotary motion. With a few exceptions, there is the option of mechanical end stops. These are particularly useful for setpoint devices (manual adjusters). One example is the ETAM25 series from MEGATRON which has mechanical end stops.
Information on electrical and mechanical angle of rotation and direction of rotation of the ETAM25 series
Electrically effective angle of rotation
The electrically effective angle of rotation is the angular range in which the output signal changes. The following illustrations show exemplary signal output functions of singleturn absolute encoders. In both cases the mechanical angle of rotation is 360°.
Example 1
Example 2
- In the first example, the encoder signal changes over the entire angular range of 0...360°. The range shown in orange is the electrically effective angle of rotation.
- In the second example, by programming the output signal differently, there are two different areas where a signal change occurs: Here the electrically effective angle of rotation is in the range between 0°...90° and between 180°...270°.
Sense of rotation (CW/CCW)
When programming the output signal curve, it is important to specify the sense of rotation of the desired output signal curve. The sense of rotation must be specified when describing the desired output signal curve so that an unmistakable relationship is established between the signal and the direction of rotation of the shaft.
The direction of rotation of the shaft is specified when the encoder is viewed from the front. That is, when the observer looks at the shaft bearing and the shaft end. With a kit encoder (without its own shaft), the observation is made on the side of the housing facing the magnet.
A distinction is made between clockwise and counter-clockwise. For the description, the abbreviations CW for clockwise and CCW for counter-clockwise have become established. The adjacent graphics illustrate the difference in the signal curve using the example of a single-turn absolute encoder. The sense of rotation CW or CCW can be selected for almost all absolute encoders by the customer when configuring the encoder.
Resolution and update rate
Digitally operating devices process the measurement signals with a certain resolution. For absolute encoders with digital signal processing, two parameters are relevant, which can also be found in the encoder data sheet:
The resolution (in bit)
- The higher the resolution of a digitally operating sensor, the finer analogue signals can be processed. Analogue output curves of digital devices therefore always have a fine step (staircase formation). The height of those steps is determined by the resolution of the sensor.
The update rate (in microseconds [µs] or milliseconds [ms])
- Signals from digitally working sensors are always transmitted with a certain time delay.
If this information can be found in a data sheet of an encoder, this is an indication that it processes data digitally. A detailed description of the meaning of these values and sample calculations can be found in the absolute encoder guide.
Protection against environmental influences / IP protection
IP stands for Ingress Protection. The IP grade specifies what measures are in place to protect shaft bearings, housings and the electrical connections against penetrating solids and fresh water of a product. One speaks formally correctly of the IP protection class of a product.
The consideration for the protection of liquids only refers to fresh water. All other media such as oils, salt water, suspensions, alkalis or acids are excluded from consideration.
The IP specification consists of two digits, which are followed by the two letters "IP":
- First digit: Protection against penetrating particles
- Second digit: Protection against ingress of fresh water
Fully sealed ETx25K Hall kit encoder: Caution, the magnet is exposed. The sealing is only valid for electronics and housing.
Distinction of IP protection
Shaft side, rear side or IP protection of the electrical connection
For contactless angle encoders, in addition to the total value for the product, a distinction is made between shaft-side IP protection, rear-side IP protection and IP protection of the electrical connection. However, in the case of an electrical connection cable with tinned cable ends, the cable ends are excluded from the IP protection consideration.
IP protection observed with one shaft in motion and at standstill
For angle encoders with their own shaft bearing, a distinction is often made between the protection class for the shaft in motion and the shaft at standstill. In these cases, the information is defined by the letters "M" for movement (shaft in motion) or "S" stop (shaft at standstill) following the IP protection numbers.
A higher shaft-side IP protection for a stopped shaft can be relevant if the encoder is part of an application/plant which is only cleaned during a (plant) standstill.
Electrical connections
Supply voltage
All contactless angle encoders require a direct voltage (DC) as supply voltage (VSUP) for operation. A distinction is made between rotary encoders that have a supply voltage change within a defined range if
- there is a ratiometric relationship to the output signal
- no ratiometric relationship exists, i.e. has no influence on the output signal
With a ratiometric relationship between supply voltage and output signal, the output signal changes in the same multiplicative ratio as the supply voltage. This option is only available for absolute encoders with analogue signal output.
Furthermore, not all available supply voltage ranges can be combined with every output electronics. When selecting the supply voltage, it should therefore be checked whether the desired output circuitry is available for the desired supply voltage. The data sheet of the angle encoder provides information about the possible combinations.
Redundancy
Some applications require redundancy of the sensor signal. The following objectives are often the reason for using redundant encoders:
Increasing the availability of systems
- The double design of the sensor reduces the probability of system failure. If one of the two lines fails, an error is logged. However, the machine or plant can continue to run until the next maintenance interval, where the sensor is replaced without loss of machine time.
Increase of the operational safety
- When operating safety-critical machines (e.g. vehicles, aviation, etc.), a failure can be fatal. The redundancy enables a safe, controlled shutdown of these machines or systems until the sensor is replaced. Redundancy is mandatory for many applications of this type.
If it is not possible to install two encoders in principle, it is possible to implement encoders with two separate supply voltages and separate ground (GND) for the operation of the encoder, which provides an electrically isolated, additional electronics.
- With magnetic angle encoders, the magnet is always installed at the end of the shaft. Therefore, it is not possible here to lead the shaft through the housing to another sensor. The magnetic sensor element itself is double/redundant and for some models galvanically separated as an option.
- With optical angle encoders it is possible to realize tandem versions, which mechanically only have the shaft in common, but are otherwise completely doubled.
Signal outputs
The following signal outputs are available for contactless absolute encoders.
Analogue:
- Voltage output (different ranges, ratiometric, non-ratiometric)
- Current (0...20 mA, 4...20mA,...)
- Pulse width modulation (PWM)
Digital:
- SPI: Serial Peripheral Interface
- SER: Special form of the SPI format
- SSI: Synchronous Serial Interface
The following output circuits are available for contactless incremental encoders:
- OC (Open Collector, Pull Up resistor not integrated in encoder)
- Voltage Output (Open Collector circuit incl. pull-up resistors integrated in the encoder housing)
- TTL (Transistor Transistor Logic)
- PP (Push Pull)
- Linedriver
Cabling
Cable lengths and cable tolerances
For electrical connection cables (tolerances) of angle encoders, other guidelines apply than for encoder housings and shafts. Note: If the line tolerances are not explicitly mentioned in the data sheet, the IPC / WHMA-A-620 applies:
| Cable length | Permissible tolerance of the connection cable (incl. plug) |
| ≤0.3 m | +25 mm -0 mm |
| >0.3 m...1.5 m | +50 mm -0 mm |
| >1.3 m...3 m | +100 mm -0 mm |
| >3 m...7.5 m | +150 mm -0 mm |
| >7.5 m | +5% -0% |
Cable Shield
For MEGATRON angle encoders with metal housing, the connection cable is shielded by an external cable shield. With all angle encoders in a plastic housing, the connection cable is not shielded.
Designs of rotary encoders
Encoders are offered in a wide variety of housing designs. They can be divided into kit encoders (without shaft bearing), and encoders with shaft bearing. In the latter case, a distinction is made between versions with plain bearing or ball bearing, and solid or hollow shaft.
Kit-Encoder
MAB12AH series magnetic kit encoder
Kit encoders have no shaft and therefore no shaft bearing. For these encoders the term "encoder with external shaft bearing" is also used because the bearing is not part of the encoder. With magnetic encoders a magnet is fixed to the end of the shaft, with optical kit encoders the encoder disc is fixed to the shaft in the application. Kit encoders are suitable for highest speeds up to many thousands of rpm and are practically not subject to mechanical wear.
Due to the lack of mechanical connection between the magnet and the encoder, the following decouplings can be realized:
- Mechanical decoupling
- Galvanic decoupling (no electrical potential reference between shaft and encoder)
- Thermal decoupling
Encoders with bearing - "shaft encoder" and "hollow shaft encoder"
These encoder types have their own shaft bearing. A distinction is also made between two designs: Encoders with solid shaft (then often just called "shaft") and encoders with hollow shaft.
The versions with solid shaft are also called shaft encoders. For shaft encoders, the term "angle encoder with integral bearing shaft" is also used.
Hollow shaft encoders on the other hand, as the name suggests, do not have a solid shaft. An application-side shaft is inserted into the hollow shaft and attached to it. For versions with through holes, it is even possible to push the shaft completely through the encoder, which can then be freely positioned axially.
Installation and mounting
The possibilities of mechanical mounting of the encoder in the application depend on the design of the encoder housing. MEGATRON offers a total of five different mounting options for its contactless encoder families. The mounting can be done by means of
- Bushing
- Flange
- Threaded holes
- Synchro flange
- Mounting ring
- Spring plate
Central thread and union nut (bushing)
The version with central thread is a very easy and quick fastening method. For mounting an encoder with bushings, generally only one single hole has to be drilled in the mounting plate of the application. The bearing bush of the encoder is guided through this hole until the face of the encoder housing or the surface of the centring collar rests on the mounting plate. Finally, the encoder is fastened to the mounting plate by means of a union nut and shim/locking washer. The union nut and washer are often included in the scope of delivery.
Some encoder families also have an anti-rotation pin. This prevents unintentional rotation of the encoder housing around the centre axis during fastening of the union nut. An additional second hole for this anti-rotation pin must be drilled in the mounting plate. In addition, the anti-rotation pin (if present) fulfils the function of a zero point reference (0° position).
To fix the encoder in a mounting plate, the hole breaks through the mounting plate completely. This can facilitate the penetration of liquids and dust from the front to the back of the mounting plate. To prevent this, an additional sealing element is optionally included in the scope of delivery, which is inserted between the front of the encoder and the mounting plate. This sealing element is an option for the ETx25 encoder family, for example.
Absolute encoder series ETA25 with central thread (bushing)
Flange mounting
Flange mounting is a widely used, simple mounting method that prevents the encoder housing from twisting around the centre axis during mounting. To fasten the sensor, three holes must be drilled in a mounting plate in the application. One hole is required for the centring collar or the central thread and two more are needed for fastening the encoder by means of screws. The screws for fastening are usually not included in the scope of delivery.
Mounting with threaded holes
Fastening by means of threaded holes is a very safe method and is based on commercially available standard parts. To fasten such encoders, at least three holes must be drilled in a mounting plate in the application: One hole for the centring collar and two additional holes for mounting the encoder. A threaded hole in the encoder housing serves as a zero reference (0° reference). The screws for fastening are usually not included in the scope of delivery.
Servo flange
This mounting method allows the zero point (reference point) to be changed subsequently by rotating the encoder housing, and is therefore particularly useful for absolute encoders. At least four holes must be drilled in a mounting plate for mounting.
- One hole for the centring collar, which completely penetrates the mounting plate and
- three additional holes on the back of the mounting plate for screwing the clamps, which do not have to penetrate the mounting plate.
The synchro clamps are not part of the scope of delivery and can be ordered from MEGATRON as accessories. By means of the terminals, the encoder is fixed by the contact pressure against the mounting plate. The fourth threaded hole in the encoder housing serves as a zero point reference (0° reference).
Mounting by means of a mounting ring
This mounting method is limited exclusively to encoders without shaft bearing (kit encoder). For mounting, at least three holes must be drilled in a mounting plate: One hole for the centring collar, which completely penetrates the mounting plate, and at least two additional holes on the back of the mounting plate for fixing the mounting ring, which do not have to penetrate the mounting plate. If the encoder is initially loosely attached with the mounting ring, this allows the encoder to be rotated around the centre axis to align the zero point (i.e. especially useful for absolute encoders). The position is then fixed simply by tightening the screws.
MxB22 series kit encoder with mounting ring
Spring plate assembly
This mounting method is only used for hollow shaft encoders. The advantage of this method is that mechanical influences on the encoder caused by radial and axial eccentricities of the application-side shaft can be minimized, which reduces the load on the bearing. This mounting method requires at least 2 holes for mounting the encoder.
Product customization
For over 60 years, MEGATRON has been a reliable partner for your design-in. In addition to the various options of our sensors, we also offer specific designs starting from small quantities, which are exactly tailored to your application requirements. Whether it is a project in the early phase or a series production - we will be pleased to accompany and support you.
