Precautions for selection and use of the hottest a

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Precautions for the selection and use of absolute incremental encoder

I. Q: what are the precautions for the selection of incremental rotary encoder

three parameters should be paid attention to:

1. Mechanical installation size, including positioning seam, shaft diameter and installation hole position; Cable outgoing mode; Installation space volume; Whether the protection grade of working environment meets the requirements

2. whether the resolution, that is, the number of pulses output per cycle when the encoder works, meets the design accuracy requirements

3. electrical interface, encoder output modes commonly include push-pull output (F-type HTL format), voltage output (E), open collector (C, common C is NPN tube output, C2 is PNP tube output), and long line driver output. Its output mode shall match the interface circuit of its control system

II. Ask: how to use the incremental encoder

1, the incremental rotary encoder has a difference in resolution, which is measured by the number of pulses generated per cycle, ranging from 6 to 5400 or higher. The more the number of pulses, the more the global electrolyte sales is 117000 tons, and the higher the resolution; This is one of the important bases for model selection

2, the incremental encoder usually has three signal outputs (six differential signals): A, B and Z. generally, TTL level is adopted. A pulse is in front, B pulse is behind, and a and B pulses differ by 90 degrees. Each circle sends out a Z pulse, which can be used as the reference mechanical zero position. Generally, we use a ahead of B or a ahead of B ultrasound to judge the direction. Our incremental encoder is defined as the shaft end, so the encoder rotates clockwise as a positive rotation, a ahead of B is 90 °, and vice versa. A ahead of B ultrasound is 90 °. There are also differences, depending on the product description

3, PLC is used to collect data, and high-speed counting module can be selected; The industrial computer is used to collect data, and the high-speed counting board can be selected; It is suggested to use the input port with optocoupler to collect data with single chip microcomputer

4, it is suggested that the B pulse should be a forward (forward) pulse, the a pulse should be a reverse (backward) pulse, and the Z origin zero position pulse

5, set up a counting stack in the electronic device

III. about outdoor use or use in harsh environments

a friend came to email and asked that his equipment was used in the field, and the on-site environment was dirty, and he was afraid of damaging the encoder

our company has aluminum alloy (special requirements can be made of stainless steel) sealed protective shell, double bearing heavy-duty encoder, which is not afraid of dirt when placed outdoors, and can be used in steel plants and heavy equipment

however, if there is space for the installation part of the encoder, I still suggest adding a protective shell outside the encoder to strengthen its protection. Unexpectedly, the encoder is a precision component, and there is still a certain gap between the value of an encoder and a protective shell

IV. from proximity switch, photoelectric switch to rotary encoder:

positioning in industrial control, the application of proximity switch and photoelectric switch has been quite mature and easy to use. However, with the continuous development of industrial control, there are new requirements. In this way, the application advantages of using rotary encoder are highlighted:

Informatization: in addition to positioning, the control room can also know its specific location

flexibility: the positioning can be flexibly adjusted in the control room

convenience, safety and longevity of on-site installation: one way to eliminate the size of the fist is to open a rotary encoder with the air release screw of the oil pump, which can measure the distance from several to dozens or hundreds of meters, and N stations. As long as the safety installation problem of a rotary encoder is solved, it can avoid the trouble of mechanical installation of many proximity switches and photoelectric switches on site, which are easy to be damaged and troubled by high temperature and moisture. As it is a photoelectric code disk, there is no mechanical loss. As long as the installation position is accurate, its service life is often very long

multifunction: in addition to positioning, it can also transmit the current position remotely and convert the movement speed, which is particularly important for the application of frequency converter, stepping motor, etc

Economy: for multiple control stations, the cost of only one rotary encoder, as well as the more important installation, maintenance and loss costs are reduced, and the service life is increased. Its economy is gradually highlighted

with the advantages mentioned above, rotary encoder has been more and more widely used in various industrial control occasions

v. about power supply and connection between encoder and PLC:

there are three kinds of working power supply for general encoder: 5VDC, VDC or VDC. If the encoder you buy uses VDC, you can use the 24V power supply of PLC. It should be noted that:

1. The current consumption of encoder is within the power range of PLC

2. If the encoder is output in parallel, connect the i/o point of PLC. It is necessary to know whether the signal level of the encoder is push-pull (or push-pull) output or open collector output. If it is open collector output, there are two types: n-type and p-type, which need to be the same as the i/o polarity of PLC. If it is a push-pull output, there is no problem with the connection

3. if the encoder is a driver output, the general signal level is 5V. Be careful when connecting. Do not damage the signal end of the encoder by letting the 24V power level string into the 5V signal wiring. (our company can also make wide voltage driver output (VDC), which should be noted when ordering)

VI. in many cases, the encoder is not broken, but just the cause of interference, resulting in bad wave shape and inaccurate counting. How to judge? Thank you

the encoder is a precision component, which is mainly due to the serious interference around the encoder, such as whether there is interference caused by the frequent starting of large motors and electric welding machines, whether it is transmitted in the same pipeline with the power line, etc

it is also important to choose what kind of output to resist interference. Generally, the anti-interference of output with reverse signal is better, that is, a+~a-, b+~ can measure the tensile strength, specified non proportional extension strength, elastic modulus, elongation and other mechanical properties of steel strand, b-, z+~z-, which is characterized by adding 8 wires of power supply, rather than 5 wires (zero in total). The transmission with reverse signal in the cable is symmetrical and subject to little interference. Judgment can also be added in the receiving equipment (for example, when the signal of the receiving equipment uses the 90 ° phase difference of a and B signals, and reads the four states of level 10, 11, 01 and 00, it is counted as an effective pulse. This scheme can effectively improve the anti-interference performance of the system (accurate counting))

even the encoder is good or bad. Its code disk electronic chip internal circuit signal output varies greatly. Otherwise, how can a 1000 line incremental encoder vary from more than 300 yuan to more than 3000 yuan

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