Dynamic Calibration Equipment for Sensors - Shakers

Dynamic calibration equipment for sensors - Shakers

Shakers are important equipment for the calibration of acceleration sensors, velocity sensors, displacement sensors, force sensors and pressure sensors for vibration and shock measurements.

1.Usage

Yangzhou Xiyuan DC series of small electrodynamic shaker is a kind of electrodynamic converter, that is, the electrical energy is converted into mechanical energy, the specimen to provide excitation force of a device. It can be used as a vibration table, small instruments, parts for environmental vibration testing, fatigue testing and on-site calibration of the sensor.

2.Technical indicators

3.Working Principle

When the power amplifier supplies the moving coil variable frequency current, according to the law of electromagnetic induction, it can be obtained:

(1) F=0.102 BLI×10                                            

(2) Fmax=0.102 BLImax×10 Where.

Fmax is the maximum value of the excitation force F (Newton), that is, the so-called maximum excitation force

B is the average magnetic induction in the working air gap (Tesla)

I is the instantaneous value of the current supplied by the power amplifier (amperes)

Imax is the maximum magnitude of the current I (amperes)

L is the effective length of the coil wire cutting the magnetic lines of force (meters)

(1), (2) formula can be obtained α = F / I = Fmax / Imax = 0.102BL × 10 For each type of shaker, B, L are constants, so α that is a fixed value. Usually called the force constant of the shaker.

4.Shaker Control Methods

1）. Acceleration input control: this is the most common control method, that is, the acceleration sensor is placed on the connection surface of the device under test for feedback control; for multi-point connection, and the connection point is far away from the device under test, usually also take multi-point control (multi-point average or multi-point maximum value, etc.);

2）. force limit control: for some more complex dynamic coupling situation, will be added to the vibration table force sensors to achieve this kind of control; based on the measured interface dynamic force, increase the test bench and the test object between the force limit control, can be limited to slow down the test of the test over-testing or under-testing; due to the technical capabilities of the force limit control is used less;

3）. Acceleration limit control: for some special equipment, according to measured data, in a specific location to increase the acceleration limit control; usually require the smallest possible modification of the input spectrum; this method is also called “limit”, can effectively protect the equipment under test does not experience excessive load;

4）. Acceleration response control: based on measured data, some positional response of the device as a control; this control is not common, generally for the connection bracket dynamics of more complex systems will be used in this way, such as the aircraft combination of outboard and so on;

5）. Open-loop waveform control: usually the shaker is a closed-loop system work, this approach generally simulate short-term or transient random vibration.

5.Main characteristics

1). Spring Characteristics In order to reduce the zero-order resonance peaks, eliminate the resonance of the springs themselves, and reduce nonlinear harmonic distortion, two sets of linear springs are used as the suspension for the moving coils of the shaker.

2). Frequency Response Characteristics The zero-order intrinsic frequency of the moving parts of the shaker is different. This resonant frequency will not affect the test results when exciting large specimens or when using force transducers to measure the frequency response function of the specimen.

3). force constant α due to the number of turns of the coil of each shaker, the magnetic induction intensity does not exactly match, so the force constant of each shaker is slightly different, labeled in the certificate of conformity of the force constant is in the displacement S = 0, that is, the vibration of the shaking table moving coil is in the neutral position of calibration.

4). Magnetic field shaker magnets using rare earth materials, a neodymium boron as a magnet. The magnets will maintain a highly stable magnetic induction strength after magnetization and aging on a special device.

6.Utilization

A. The shaker can be suspended in one of the following three ways:

(1) The shaker is rigidly fixed to the floor. This method of fixing requires that the resonant frequency of the vibration system in the form of the shaker and supports, fixtures, etc., be 3-4 times higher than the operating frequency of the shaker. For this reason, bulky, rigid stands and fixtures are used wherever possible. For non-temporary fixing or shakers working at fairly low frequencies, this method is more appropriate.

(2) The shaker is elastically fixed to the floor. This fixing method requires that the resonant frequency of the vibration system formed by the shaker and the spring is 3-4 times lower than the lowest operating frequency of the shaker. For this reason, the shaker is usually connected to the support by a rubber cord or metal spring. This method facilitates multiple installations and greatly reduces the transfer of energy from the shaker to the ground. It is recommended that this method be used whenever possible when the shaker's operating frequency is f > 5 Hz.

(3) The shaker is elastically fixed to the specimen itself. This method requires that the resonant frequency of the vibration system formed by the shaker and the spring be 3-4 times lower than the lowest operating frequency of the shaker. For this reason, the shaker must also be suspended from the specimen by a rubber cord or metal spring. This is the only method that can be used when the shaker cannot be fixed to the ground by either method, such as on bridges, wings in flight, and other free-hanging structures.

B. Shaker-to-specimen connection

The connecting rod supplied with the shaker is used exclusively to connect the shaker to the specimen. The connecting rod serves primarily to transfer the excitation force to the specimen, but it also serves to protect the shaker (if the direction of excitation of the specimen is not in line with the axis of the shaker due to improper installation of the shaker, the connecting rod will be bent or even broken, resulting in damage to the shaker). The connecting rod must be connected to the specimen and shaker in such a way that the supporting spring is unloaded or lightly loaded. Once connected, a nut must be attached to each end of the connecting rod to prevent loosening due to vibration.

C. Maximum Travel Limit

If the shaker exceeds the maximum travel, the moving coil skeleton will hit the limiter and make a clattering noise. When this noise is heard, the excitation current must be reduced quickly to avoid damage to the shaker.

D. Maximum current limit

This shaker is used with the XY-series power amplifiers. Regardless of what power amplifier is used, the current through the moving coil must be monitored. Long time use should be less than the maximum allowable RMS current, short time use can be used in the maximum RMS current. (Forced ventilation is preferred).

E. Forced ventilation    

In order to ensure the stability of the coil work, can be forced ventilation, in the bottom of the vibration table has a screw, remove the air can be sent. (Pressure greater than 0.5 atmospheres, flow rate of 60-80 kg / min)

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