The Tips And Attention For Vibration Testing ?
Basic Exciter Instrumentation
A basic set-up consists of an exciter, a power amplifier, an exciter control, an accelerometer or force transducer and a conditioning amplifier. The exciter is selected primarily according to the force or acceleration required, but other parameters may be important such as Its abiUty to take up side loads, the transverse vibration and the distortion of the waveform.
The exciter Is Isolated from its base by springs, in most cases giving sufficient protection from environmental vibration when bolted directly on the floor. However, to reduce the vibration transmitted to the building by exciters used for high level applications, the exciter must be
mounted on resilient material or a seismic block.
Sine Excitation
Sine signals, swept or at a single frequency, are by far the most commonly used excitation Inputs: the control is relatively simple, a large amount of reference material exists, and the response Signals are easy to measure. When the signals are swept, a feedback control, known as a compressor Is applied. The demand to the compressor is that it should be fast enough to react to low damped resonances even at high sweep rates. A dynamic range of at least 80 dB and compressor rates up to 1000 dB/sec are normally found. Sine signals are described by their frequency and amplitude. In Vibration testing the amplitude is normally In terms of peak values (displacement as peak-peak) with
frequencies ranging between 2 and 10,000 Hz.
Random Excitation
A random signal used in vibration testing has a continuous spectrum, with amplitudes varying according to a Gaussian distribution. Within the specified frequency range any amplitudes should be present, but in practice the generators and amplifiers will give limitations. In vibration testing It is generally demanded that a random Signal should contain peak-values of three times the RMS value.
The force produced by an exciter is mainly limited by the heating effect of the current. i.e. the RMS value. whereas the power amplifier rating is influenced by the peak values. To give the same force the amplifier must therefore be larger when used with random than with sine
excitation. The random spectrum is described by its power spectral density or acceleration spectral density. ASD (m/s2)2/HZ. To shape and control this. the vibration must be analyzed by a narrow band analyzer and compressor loops applied to each bandwidth. Digital tech
niques based on Fourler transforms are normally used and the control is achieved using a computer, a process called equalization.
The random capacity of an exciter is specified as the maximum acceleration spectral density at different loads of a spectrum, shaped according to the Internaional Standard, ISO 5344.
Environmentall Testing
An environmental test Is performed to determine the ability of equipment to withstand specified severltles of vibration, shock, temperature, humidity, etc. The requirements may be set by the user or the supplier with reference to some national or military standard. These standards describe the test procedures, but do not state the individual test levels.
The fundamental standards are IEC 60068, tests Fc and Fd, which in several countries have been accepted as national standards.
The contents of all standards largely fall Into 3 groups:
-The mounting of the test object,
-The endurance conditioning and the vibration response investigation.
-Mounting of the Test Object
As the test Is performed to simulate the environmental influence, the object must be mounted on the exciter table by its normal means of attachment. In most cases ,this requires a special fixture, which allows the specimen to be vibrated along the specified axes.
The method of mounting must be described in the test, and so must the point on the specimen to which the control accelerometer is attached. Also, It must be specified whether the object should be operating during the test.
Fixture
In cases where the test object cannot be mounted dIrectly on the exciter table a fixture, sometimes Of a rather complex nature. is required for fastening the object. The fixture must be stiff enough to transmit the generated force or motion uniformly to the test object. thus not
Introducing any resonances. It is important to check the design by measuring the vibration levels on the surface of the fixtures by means of accelerometers. All resonances must tie outside the test frequency range. The natural frequency of a construction will be almost the same whether the material is steel or aluminium and as the total weight of test object and fixture is a restricting tactor in the application of an exciter. aluminium will normally be the best choice. To obtain a high resonance frequency. it wilt always be necessary to over-dimension the structure, so no considerations normally have to be taken concerning the mechanical strength.
For minimizing the weight of the fixture, it can be constructed of relatively thin plates, supported by braces. The plates are of Simple geometric shapes with responses easy to calculate. Much care should be taken In assembling: bolts can introduce spring/mass effects, weld
ing can introduce Internal stresses. If resonances cannot be avoided the damping can be Increased by laminating with a damping material such as rubber or by filling cavities with foamed plastic.
| Shaker Model | JQA-202-335 JQA-203-335 |
| Frequency Range (Hz) | 5~3000 |
| Rated sinusoidal force (KN) | 20 |
| Shock force (KN) | 40/60✱ |
| Max. acceleration (m/s²) | 980 |
| Max. speed (m/s) | 2 |
| Max. displacement (mmp-p) | 51/76 |
| Max. load (kg) | 300 |
| Vibration isolation frequency(Hz) | 2.5 |
| Shaking table type | JQ-20 |
| Moving parts weight (kg) | 23 |
| Armature diameter (φmm) | 335 |
| Allowable eccentric moment (N x m) | 490 |
| Outer dimension (W·H·D) (mm) | 1080*990*860 |
| Shaker weight (kg) | 1600 |
| Power amplifier model | PA-20 |
| Max. output power (KVA) | 20 |
| Amplifier Size (W·H·D) | 550*1750*850 |
| Power amplifier Weight (kg) | 410 |
| Power Amplifier working model | Switch |
| System power consumption (KVA) | 40 |
| Cooling method | Forced air cooling |
| Fan model | FJ-3000 |
| Rated flow (m³/min) | 40 |
| Rated wind pressure (kPa) | 3.5/8.8 |
| Fan power (KW) | 7.5 |
Guangdong Jianqiao Testing Equipment Co.,Ltd is a large scale professional manufacturer specializing in R&D ,production and sales of vibration test system,environmental test chamber and battery testing equipment.With the advantage in Technicians in R&D department,professional production and sales teamand perfect after-service department.and several ,senior R&D Engineer haired across the country .Our marketing network covers major large and medium-sized cities among the country. In the past 20 years, Jianqiao provide high quality products and one -stop solutions for dozens of top 100 enterprises and 11289 end users.
The company manufactures all kinds of vibration and environmental testing equipment in strict accordingwith ISO9001 and products meet the standard of ISO, ASTM , DIN ,EN , BS , UL , JIS , GB/T , GJB,JIS,ANIS,UL,IEC etc. and other domestic and international standards .Our products are widely used in New energy vehicles, aerospace, - shipping, electronics industry and other industries, and are applicable to all scientific research units, quality inspection institutions and academic fields.
