First, differential transformer (LVDT) high-precision digital series displacement meter main features
The high precision digital displacement meter consists of a differential transformer (LVDT) and an electrical measuring instrument. The electrical measuring instrument is composed of an electronic measuring circuit and a digital panel meter. Among them, LVDT is a sensor that turns the measured displacement into an electrical signal. It is used to measure the deformation (displacement) produced by various models, specimens, rock mass, concrete, metal or non-metallic materials under the action of force or temperature, and to measure the deformation of various materials over time ( Creep) In the electro-hydraulic servo system for displacement detection, etc., it is also possible to measure various physical quantities, such as pressure, force, tension, and liquid level changes, which are previously converted into linear displacements. The output signal of the displacement meter is convenient for wired telemetry, automatic control, digital instrument display, recording with XY function, easy to communicate with the computer interface for data acquisition, processing and control, etc., which can meet modern scientific research, industrial and agricultural production and national defense construction. The need for precise measurement and automatic control of the amount of displacement.
1. When the LVDT housing is clamped to the reference object that is considered to be stationary, the measuring rod can be rigidly connected to the measured object (non-rebound type), or it can rely on the built-in return spring of the sensor (rebound) Equation) By placing the rod on the measured point, you can directly measure the displacement relative to the reference. However, the rebound type sensor may have a hysteresis when measuring the rapidly changing dynamic displacement due to the large spring inertia.
2. Use of YWDA series sensors:
The YWDA series is a mechatronic product that encapsulates the sensor and transmitter in the same housing. The shape of this product is slightly longer than the YWGA type, but it is convenient to use. It is powered by three cores (positive, negative, ground) in the five-core shielded cable, and the other two cores are signal output, which can be directly connected to the secondary instrument or computer. The YWDA and SMA series sensors are separate products from the transmitter and the sensor. The two are connected by a six-core cable. The transmitter is a 70×60 rectangular circuit board with a gold finger plug. The circuit board can be installed in a small metal box, and the two sides of the box are respectively equipped with a sensor and a socket for external power supply and output signals. When supplied, the board can also be placed in a small metal box. The board has a socket that can be installed in the user's cabinet or chassis. The probe of the sensor is a semi-circular carbide type.
3. Secondary instruments matched with it:
(1) YWGA, and SMA sensors can be equipped with 5CB-10C precision digital displacement meter (can work with 1 to 30 sensors at the same time), and the displacement meter is equipped with 4 1/2 digits (full scale display ±19999) LED (LED) digital display with a key switch to switch between different sensors, the meter number shows the corresponding sensor displacement reading. At the same time, the real-time signal output of all sensors on the rear panel of the displacement meter is collected by the computer. The displacement meter uses 220V ± 10% AC power supply, and the internal voltage regulator circuit can supply power to the sensor, no need for other power supply.
(2) DB-6D multi-point displacement meter is a portable, 4 1/2 digit liquid crystal display with built-in rechargeable battery, suitable for use in environments without AC power.
(3) Use the small metal transmitter box described above.
(4) YWDA type sensor can directly connect to the microcomputer through a dedicated external real-time acquisition 16-bit A/D converter board, sampling time 10μs, 16-channel analog input, 12V power supply, and parallel communication with the computer. A set of acquisition software is included with the card, which is graphically displayed, full-featured and easy to operate.
4, sensor use precautions
(1) Please do not let the moving iron core and the measuring rod be deformed and bent due to the large direction finding force, otherwise the flexibility of the rod activity will be seriously affected. The housing of the sensor is a highly magnetically permeable material and should be protected from falling and impact. Please take care.
(2) The sensor stem (head) should be in vertical contact with the object under test. The point to be measured should be on a plane with a certain degree of finish.
(3) When clamping the sensor housing before measurement, avoid looseness, but the force is too large and too strong, and the housing may not be sunken or deformed.
(4) The effective working section of the sensor is generally in the middle of the active area of the pole. The probe is not a valid working area in the vicinity of the fully extended and fully compressed sections. When installing the sensor, adjust the position of the sensor (moving) so that the displacement does not change beyond the effective measurement range. The displacement reading can be observed so that the displacement is within a predetermined change and the signal output does not exceed the rated range.
(5) If the rod is found to be affected by dust or oil adhesion, please wipe and clean the rod with alcohol cotton, but the sensor should not be disassembled to avoid damage or reduce the measurement accuracy.
(6) A linear power supply is recommended for the external power supply. If a switching power supply is used, the clutter (interference) voltage in the signal output will increase significantly. The requirements for the stability of the external power supply voltage of the circuit board are selected according to the accuracy and stability requirements of the measurement. For the high requirements, a linear power supply with good stability should be selected. The actual power consumption of each board is no more than 10mA. (But the actual power supply should have a margin, preferably not less than 50mA).
(7) If the data acquisition system is connected, the slope can be corrected in the software. Calculate the correction factor according to the data in the factory test report, and multiply it by the collected data. If you have any questions, please call us in time, thank you!
Third, the measurement demonstration process description
When the measured object moves from right to left and contacts with the sensor probe in the horizontal direction, the sensor will display the measured object relative to (by sandwiching) on the 5CB-10C precision digital displacement meter. The displacement value of the yellow bracket on the sensor housing (considered to be the reference).
When the measured object continuously moves to the left, the displacement value displayed on the instrument gradually increases from small to large, until the measured object does not move left and right, and the displayed value reaches 5.000 and remains unchanged.
After that, the object is no longer moved left and right, and soon it begins to produce a process of up and down vibration. The vertical direction sensor is fixed by the connecting rod and the green column, and the column can move up and down, so that the sensor head can not only touch the surface of the object to be tested, but also can continue to move down, and finally the column is fixed at an appropriate position. The reference point of vibration.
The oscilloscope (or computer) displays a horizontal line when the measured object has not yet generated up and down vibration or the sensor probe is not in contact with its surface.
When the measured object starts to vibrate and comes into contact with the sensor probe, the frequency of the vibration is lower, and the displayed waveform density is sparse. At the same time, the amplitude of the vibration gradually increases from small to small, and the waveform gradually increases from small to small.
When the frequency of the vibration of the measured object gradually increases, the waveform gradually becomes dense.
When the object under test vibrates up and down strongly, the envelope of the oscillating wave then swings up and down.
After that, the vibration gradually weakens until it stops, and the amplitude of the waveform gradually decreases until a horizontal line appears.
The demo can be repeated on a weekly basis.
Through this demonstration, the LVDT can be used to accurately measure static and quasi-static displacements or dynamic displacements, as well as the geometry of objects or components. This demonstration device can be modified to automatically sort the mechanical components.
Fourth, the working principle
The differential transformer displacement sensor (LVDT) is an electromagnetic induction principle. Unlike a conventional power transformer, the LVDT is a measuring component for weak magnetic coupling of an open magnetic circuit. It uses epoxy glass cloth, stainless steel and other materials as the coil bobbin. With a different wire diameter enameled wire, a set of primary coils are wound on the skeleton, and two sets of secondary coils, the working mode of which depends on the movement of the magnetic core in the bobbin. When the primary coil supplies an alternating voltage (excitation voltage) of a certain frequency, the movement of the iron core in the coil changes the magnetic field distribution of the space, thereby changing the mutual inductance between the primary and secondary coils, and the secondary coil is generated. Inductive electromotive force, with different positions of the core, the mutual inductance is different, and the induced electromotive force generated by the secondary is also different, so that the displacement of the iron core (the actual iron core is kept in contact with the measured object through the measuring rod, That is, the displacement of the measured object becomes the voltage signal output. Since the voltages of the two secondary coils are opposite in polarity (see Figure 1), the output of the sensor is the difference between the voltages of the two secondary coils, and the voltage difference is The amount of displacement is linear. When the iron core is in the middle of the coil, the two-stage coils induce equal voltages but opposite phases, and the voltage difference is zero. When the iron core moves to the right, the voltage induced by the right secondary coil is greater than that of the left side, and the voltage difference between the output of the two coils varies linearly with the displacement of the core (the solid portion of the first quadrant), which is effective for the LVDT. Measuring range (half). When the iron core continues to move to the right, the difference between the output voltages of the secondary coils is not linear with the core displacement, which is a buffered, non-measured area (dashed line segment). On the contrary, when the iron core moves from the middle position of the coil to the left side, it is also the same. The solid line on both sides of the zero point is generally a symmetrical measurement range, except that both are AC signals with a phase difference of 180 degrees. The actual LVDT coil is usually fastened to the housing, and the iron core and the measuring rod are fastened to another body. When the relative displacement between the two bodies occurs, a displacement voltage output is generated.