The encoder is an instrument that is used to measure the angular displacement of a wheel or shaft. Encoders are found in many digital devices, and magnetic and optical encoders are particular types with pros and cons. Magnetic systems provide a very low cost for relative accuracy in position measurement but suffer from the problem of magnetic interference, which can lead to inaccuracies. Optoelectric encoders offer high levels of accuracy without interference (typically), but they are more expensive to produce, requiring higher design and manufacturing standards.
The encoder consists of a wheel or disk with slots, holes, tabs, or teeth along the rim. These slots, holes, tabs, or teeth divide the wheel into sections. The wheel is built to rotate freely and has a shaft attached. The post is connected to an output shaft that goes through the drive train. This shaft has an optical sensor that looks for a preprogrammed specific mark on the disk.
When this mark is in alignment with the sensor, it will send an electrical signal out from the encoder, indicating that the input and output are in the correct alignment. This system uses clockwise movement to track forward movement, which has advantages and disadvantages and key performance parameters.
Optical Encoders
The optical encoder is less durable than the magnetic and piezo-electric types of encoder. The optical encoders are prone to damage from dust in the air, heavy winds, mechanical shock, and vibration. Since these are magnetic sensors, the encoder must be shielded against interference, making optical speed controllers with integrated sensors difficult to produce.
Furthermore, since they use infrared light instead of regular light sources, they have difficulty reading at night or under adverse weather conditions.
Also, since they are made out of plastic materials and require electrical circuits to be hidden behind a plastic cover, they tend to get damaged or destroyed over time due to weather exposure or errors in care (if stored in an area exposed to extreme temperature changes).
Magnetic Encoders
Magnetic encoders can be very accurate if they are kept away from magnets. Magnetism affects the output, causing uncountable errors with the final calculation. The main advantage is that magnetic encoders are generally easier to install and far less expensive than other encoder systems. Magnetic encoders have a maximum speed of 20,000 rpm in the open air and 1,000 rpm when installed in a metal housing.
The encoder’s top speed can be reduced if installed in a metal housing. It will be at most that speed with the need for additional shielding. Generally, however, when dealing with steel material, magnetic encoders are less affected by steel than their counterparts. Magnetic-coupled encoders also require more bytes to be input into the encoder’s memory than optical or electronic-coupled encoders.
The magnetic encoders are also susceptible to dust, so they must be kept clean. Magnetic encoders will generally work in all temperatures except extreme heat or cold. This type of encoder is designed to work within an atmosphere range of -40 °C to 85 °C. Magnetic encoders also have a zero output when the disk goes to zero.
This means the magnetic sensor will send no signal, causing no harm to the calculation. However, additional sensors are required with this type of encoder system as there is a chance that the magnetic sensor will not be able to read properly because of rough surfaces and gaps on the disk.
Optical and magnetic encoders are commonly used to measure position, speed, and motion control in various industrial applications.
Here’s a comparison between these two types of encoders:
1. Principle of operation
Optical encoders use light and photodetectors to detect the position and motion of an object. On the other hand, magnetic encoders use magnetic fields and Hall-effect sensors to measure position and motion.
2. Accuracy
Optical encoders typically have higher accuracy compared to magnetic encoders. Optical encoders can provide resolution to a fraction of a micron, while magnetic encoders are usually limited to around 10 microns.
3. Environmental considerations
Optical encoders are sensitive to environmental factors such as dust, moisture, and temperature variations. On the other hand, magnetic encoders are less affected by these factors, making them more suitable for harsh environments.
4. Durability
Magnetic encoders are generally more durable and robust compared to optical encoders. Optical encoders are sensitive to physical impacts and shocks, while magnetic encoders can withstand harsh physical conditions.
5. Cost
Optical encoders are generally more expensive than magnetic encoders, especially for high-resolution applications. Magnetic encoders are a more cost-effective option for lower-resolution applications.
Power consumption
Optical encoders typically require more power compared to magnetic encoders, making them less suitable for battery-powered applications.
| Optical Encoder | Magnetic Encoder | |
| Working | Optical sensor detects changes in light | Magnetic field sensor detects changes in magnetic field |
| Output Signal | Digital or analog signal | Digital signal |
| Resolution | High resolution | Lower resolution |
| Accuracy | High accuracy | Moderate accuracy |
| Operating | Limited by dirt, dust, | Resistant to dust, dirt, grease |
| Environment | grease, and vibrations | and vibrations |
| Cost | Expensive | Inexpensive |
| Application | Precision measurement, robotics, automation | Harsh industrial environments, motion control, robotics |
| Ease of | Requires careful | Easy to install and use, |
| Installation | installation and calibration | minimal calibration required |
| Maintenance | Requires periodic cleaning and maintenance | Low maintenance required |
Conclusion
Magnetic and optical encoders are now commonplace; in fact, they are probably one of the most affordable and powerful solutions that can be used in a variety of situations. However, each type has its advantages and disadvantages. Optical encoders can perform extremely well under harsh environmental conditions while also being highly reliable due to their relative immunity to mechanical shocks.
Magnetic sensors are more suitable for rugged applications and can withstand more physical damage compared to other types of sensors. There is no one-size-fits-all solution, so be sure to pick the encoder that best suits your application’s needs before you install it.
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