Dec 09, 2021 
In a series of modern machinery industries like construction, building materials, mining, engineering vehicles, metallurgy, water conservancy, port machinery and other fields related to large heavy equipment, the reliability and safety of equipment comes first in process control.
For safety requirements, reliable feedback of encoder signals are directly related to control safety and reliability. Unreliable and inappropriate encoder selection will lead to frequent equipment debugging and maintenance. As a result, labor costs of debugging and maintenance may rise hugely, and on-site service engineers will never be enough.
Image 1: A sample encoder manufactured by KOYO.
So what are the techniques of selecting the right encoder?
The specific work environment of various devices determines the selection of different encoders and their transmission methods.
A.The work environment is complex. Frequency converter, large motor and high and low voltage power supply system, signal cable and power line are arranged together, making heavy electrical interference for encoders.
B.Some devices need to be moved in long-distance and are difficult to ground.
C.The distance of signal transmission is long, and the safety and reliability of signal data are required to be precise.
D. Real-time and reliable signal transmission is required to ensure secure control response.
E. Many of the encoders are used in outdoor or in harsh environment, which requires the industrial class of products.
Therefore, right selection of encoders is very important for the use of heavy machinery and equipment. Encoders can be divided into incremental encoders and absolute encoders based on signal principle.
Image 2: Three SICK encoders are used on a wind power equipment for blade adjustment and pod adaptation.
Absolute encoders have been widely used in many fields due to their in place design and excellent process performance, and have won good market reputation.
Incremental encoders convert displacement into periodic electrical signal, then transform this electrical signal into counting pulse, and the number of pulses is used to represent the displacement.
In diverse fields, there are more extensive use of encoders. Based on different uses and principles, the performance of different encoders excel in the work environment that fits them.
Here’s a comparison of the differences between these two types of encoders.
Absolute Encoder
When an absolute encoder rotates, there are one-to-one codes (binary, BCD codes, etc.) output corresponding to the position. From the change of code size, the position of the positive and negative direction and displacement can be determined without phase circuit.
An absolute encoder has an absolute zero code. After a power failure or shutdown, the code of the power failure or shutdown position can still be accurately read and the zero code in the encoder can be accurately found. When the power is turned on, the measurement is restarted.
Video 1: 3D animation of how an absolute encoder works. (Source from: learnchannel on YouTube.)
When purchasing absolute encoders, besides examining the model, the performance serial number and the number of segmentation (or digits) needs to be paid attention too.
For selection of the number (or digits) of the split, here’s a reference formula:
Number of divisions = 360°/design resolution
The output code system and output mode of the selected absolute encoder should correspond to the user's rear processing circuit.
In general, the measuring range of absolute encoders is 0°～360°, but special models can achieve multi-turn measurement.
Selection Notes about Absolute Encoders
* Parameters
When choosing an absolute encoder, you need to consider the corresponding parameters. The first is the mechanical installation size of the equipment, including the shaft hole size, installation hole position, and the corresponding outlet method that the equipment adapts to.
Second, the size and space of the equipment should meet the installation requirements of the equipment, as well as the material protection level of the equipment. Besides, it’s important to pay attention to the resolution of the device in order to ensure that the device has high-quality signal processing capabilities.
* Interface Selection
In the working process of absolute encoder, the corresponding electrical selection is used to help complete the corresponding work. Therefore in the process of selecting an absolute encoder, it is necessary to pay attention to the corresponding electrical interface, which indicates whether it matches the corresponding Voltage output and the output of integrated electrical appliances.
As a result, the output mode of the device can help the corresponding control system and circuit to match each other.
Image 3: Wiring and configuration label of a Nemicon absolute encoder.
* Choice of the Dealer
Generally, choosing equipment dealers is also an important part.
First, analyze from various practical aspects, including the market scale and reputation of the dealer, and its price positioning compared with competitors on the market. In a word, when choosing the right dealer, users need to choose the appropriate equipment and services according to their own use, so as to guarantee the future use.
Incremental Encoder
When an incremental encoder rotates, it has corresponding pulse output. Its rotation direction and the increase and decrease of pulse quantity is read by the phase judging circuit and counter at the back.
The counting point can be set arbitrarily, and it can realize unlimited accumulation and measurement of multiple turns. It is also possible to use the Z signal for each pulse transmitted as a reference mechanical zero position. When the number of pulses is fixed, the original pulse can be multiplied by the 90° phase difference A and B signals to improve the resolution.
When ordering incremental encoders, please specify the selected model, number of output pulses per revolution, power supply voltage, wire outlet mode, and signal output mode. Besides, users should know whether the mechanical installation size of the selected model can meet your requirements.
The number of output pulses per revolution should be selected according to the following formula.
Number of output pulses per revolution (P/r) = 360°/design resolution
When selecting the signal output mode, please note its match with the rear circuit. If the long-line drive output mode is selected, users should select a matching receiver so that the rear circuit can accept the data.
Image 4: Baumer Incremental encoder BHF 16.24K4096-E2-5
Selection Notes about Incremental Encoders
* Parameters
When purchasing appropriate incremental encoders, users need to consider the technical parameters. So what factors do the technical parameters of encoders include?
First of all, the installation limits and methods. Generally speaking, we will divide the installation methods of encoders into two types, base installation and flange installation. There are different characteristics with the two methods.
Secondly, the signal processing frequency of the encoder. Whether there's internal chip and relevant technical parameters of the central processing module are also factors worth paying attention to when selecting encoders.
* Quality of the Encoder
First, note the material of the encoder. Generally speaking, encoders are made of new composite materials and metal materials.
When an encoder is made, it needs to be tightly closed to ensure that the device is absolutely hermetic. The quality of encoders can also be considered from various components, so as to better meet the use of the equipment.
* Price
When choosing incremental encoder, or anything, we need to consider its price. What factors should be taken into account for this part?
The main considerations are device performance and the choice of channels. If users want the encoder to have an advantage in performance, they need to consider the market changes of encoders and make a reasonable choice according to their actual situation.
Thank you for your reading and more information please visit the website https://okmarts.com/
