大富豪棋牌游戏安卓版下载⎛⎝oYXgj⎠⎞ Simple analysis of error source of pulling rope displacement sensor

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Simple analysis of error source of pulling rope displacement sensor

Release date: June 21, 2019 Number of hits: 163

Pulling rope Displacement sensor It's also called pull wire Displacement sensor Compared with grating ruler, laser interferometer and other sensors, although its accuracy is not high, it is widely used because of its convenient installation, low price, large measurement distance, strong anti-interference ability and many other advantages.

Because the influence of various factors on the error should be considered in the process of design, installation, detection, measurement and use.

Next, through preliminary analysis, find out the error caused by different factors.

1. Principle and application of rope displacement sensor

The wire rope displacement sensor is used to measure the displacement with high flexibility and toughness composite steel wire. The steel wire is wound on the drum by spring, and Yuci changes the displacement into rotation motion. The cylinder is directly connected with a precision rotary encoder, and the displacement is converted into current, voltage or digital pulse output.

In use, the displacement sensor is installed in a fixed position, and the pull rope is connected to the moving object. The linear movement of the pull rope is aligned with the axis of the moving object. When the object moves, the displacement sensor outputs the digital signal. The pull rope displacement sensor can be used to measure the movement distance, speed, inductive position or limit sensor, calculator for recording mechanical movement times, etc. Application fields include testing, instrument calculation, transportation, robot, hydraulic device, pneumatic device, industrial automation, motion control, etc. The measuring distance ranges from tens of millimeters to more than ten meters, so it is widely used.

2. Sensor factors

According to JJF 1305-2011 "calibration specification for linear displacement sensor", the basic error of typical pull rope displacement sensor is generally between ± 0.05% ~ ± 0.5%. The parameters such as linearity, repeatability and return error should be paid attention to. In terms of linearity, attention should be paid to the difference between the percentage of full scale and the percentage of measured value. If the error cannot be confirmed, the length measuring machine and other instruments should be used to calibrate it.

In the choice of resolution, it is recommended to select the resolution according to the demand, which is enough. The theory of analog signal sensor is infinite, but it is affected by the accuracy, stability and repeatability of the instrument in practice. However, some digital signal sensors have a resolution of 0.001mm, but the sensor with high resolution may not match the display instrument with low reading speed, resulting in data loss.

Pull rope displacement sensor is divided into analog signal and digital signal according to the output signal. The analog signal is divided into voltage output and current output. Analog signal should pay attention to the problem of transmission distance, if the transmission distance is too large, it will seriously affect the accuracy. Analog signal will have the problems of signal interference, stability, drift and load size.

The digital output is divided into square wave pulse output and gray code signal. Generally, digital signal does not have signal interference, drift and other problems. The digital output sensor generally chooses the incremental type, otherwise it can not distinguish the direction.

It is necessary to pay attention to whether the stack structure of the sensor is consistent with each other.

3. Instrument factors

Attention should be paid to the matching problem with the sensor when selecting the secondary instrument. First of all, the instrument should meet the requirements of overall accuracy in the number of display digits and ratio setting digits. Some display instruments or use single-chip microcomputer ratio bit less, which affects the accuracy of adjustment. For example, the maximum allowable error of the sensor is ± 0.5%, while the ratio digit can only be adjusted by 1%, so the accuracy affected can only reach ± 0.1%.

Secondly, we should pay attention to the reading speed of counting device. The speed of the digital output sensor is seriously lost when the data is too fast. The reason for this phenomenon is that the data of display instrument or counting device is slow to read. Some meters are designed for counter, which can not be used in pull wire displacement sensor. In addition, the factor of resolution is also very important. If it needs to be applied in the situation of high speed, such as the motion speed > 0.5m/s, it is recommended to select the sensor with low resolution or the display instrument with high reading speed. In general, for 0.01mm/pulse sensor, the reading speed of the instrument is recommended to be ≥ 30Hz.

4. Influence of installation location and environmental factors

The installation should conform to Abbe principle as far as possible to reduce the system error. Abbe principle means that the standard length (standard line) should be placed on the extension line of the measured length (measured line) in the length measurement. In addition, the measurement direction of the sensor should be horizontal as far as possible. However, if the measurement distance is long and the installation is horizontal, attention should be paid to the influence of the self weight of the stay wire.

In environmental problems, attention should be paid to the effect of material expansion coefficient on accuracy. If it is used outdoors and the measurement distance is long, the influence of crosswind should also be considered.

But the influence of the above factors on the displacement sensor is relatively low. If the measurement direction of the sensor is not parallel to the movement direction, the vertical direction of the sensor is offset by 10 mm on the measuring length of 1 m (it can be observed by naked eyes obviously). However, the error is only increased by 0.05mm, that is 0.005%, which is very small compared with the error of 4-0.05% ~ 4-0.5% of the ordinary cable displacement sensor.

In addition, the corresponding protection level should be selected according to the use environment, including sensors, instruments, converters and connecting wires. In the harsh environment, if there is no corresponding protection level, the use can not be guaranteed, let alone the accuracy. The selection of stainless steel and corrosion-resistant stay wire is guaranteed for long-term use.

epilogue

Generally speaking, the factors of sensors and instruments have great influence on the overall accuracy, which should be considered emphatically. Readers can choose sensors and display instruments scientifically and reasonably according to their own situation and referring to the above points, so as to eliminate all kinds of factors affecting error and improve the overall accuracy.


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