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楼主: sundy_chinavib

关于ICP加速度传感器使用的一些疑问

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发表于 2012-10-11 23:16 | 显示全部楼层
以下内容选自mmf。de网站,介绍关于IEPE标准的,可供参考。
IEPE Standard
Metra manufactures many accelerometers featuring a built-in preamplifier. It transforms the high impedance charge output of the piezo-ceramics into a low impedance voltage signal which can be transmitted over longer distances. Metra uses the well-established IEPE standard for electronic accelerometers ensuring compatibility with equipment of other manufacturers. IEPE stands for "Integrated Electronics Piezo Electric". Other proprietary names for the same principle are ICP®, CCLD, Isotron®, Deltatron®, Piezotron® and others.
PrincipleThe built-in circuit is powered by a constant current source (see Figure 4). This constant current source may be part of the instrument or a separate unit. The vibration signal is transmitted back to the supply as a modulated bias voltage. Both supply current and voltage output are transmitted via the same coaxial cable which can be as long as several hundred meters. The capacitor CC removes the sensor bias voltage from the instrument input providing a zero-based AC signal. Since the output impedance of the IEPE signal is typically 100 .. 300 Ohms, special low-noise sensor cable is not required. Standard low -cost coaxial cables are sufficient.

                               
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Figure 4: IEPE principle
The constant current may vary between 2 and 20 mA (Do not confuse with 4 to 20 mA standard!). The lower the constant current the higher the output impedance and, therefore, the susceptibility to EMI. A constant current value of 4 mA is a good compromise in most cases.
The bias voltage, i.e. the DC output voltage of the sensor without excitation, is typically between 12 and 14 V. It varies with supply current and temperature. The output signal of the sensor oscillates around this bias voltage. It can never become negative. The upper limit is set by the supply voltage of the constant current source. This supply or compliance voltage should be between 24 and 30 V. The lower limit is determined by the built-in amplifier. Metra guarantees an output span of > ± 5 V. Figure 5 illustrates the dynamic range of an IEPE compatible sensor.

                               
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Figure 5: Dynamic range of IEPE transducers
Low Power IEPEParticularly for battery-operated equipment it may be unfavorable to provide a sensor supply with 4 mA constant current from a 24 V compliance voltage, requiring a power of 100 mW. For this reason Metra has introduced a low-power version of the IEPE standard, which is applied in some accelerometers and in some vibration meters . Low Power IEPE accelerometers usually have a bias voltage of 4 to 8 V. So a compliance voltage of 10 to 12 V is sufficient. The constant current supply may be as low as 0.1 mA, depending on the transducer model. This can reduce the power consumption of the transducer by up to 99 %.
Frequency PerformanceThe lower frequency limit of Metra´s transducers with integrated electronics is 0.3 Hz for most shear and bender accelerometers and 3 Hz for compression sensors. The upper frequency limit mainly depends on the mechanical properties of the sensor. In case of longer cables, their capacitance should be considered. Typical coaxial cables supplied by Metra have a capacitance of approximately 100 pF/m.
The nomogram in Figure 6 shows the maximum output span of an IEPE transducer over the frequency range for different cable capacitances and supply currents. With increasing cable capacitance the output span becomes lower. The reason for this influence is the reduced slew rate of the built-in amplifier at higher load capacitances. With very long cables the full output span of ± 6 V can only be reached at frequencies up to a few hundred Hertz. For a cable capacitance up to 10 nF (100 m standard coaxial cable) and 4 mA supply current the reduction of the output span can be neglected.

                               
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Figure 6: Output span of IEPE accelerometers for different cable capacitances and supply currents

Figure 7 shows the typical frequency response of the sensor electronics under the influence of different cable capacitances and supply currents. At higher capacitances the upper frequency limit drops due to the low pass filter formed by the output resistance and the cable capacitance. At 4 mA the cable capacitance can be up to 50 nF (500 m standard coaxial cable) without reduction of the upper frequency limit.

                               
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Figure 7: Frequency response of IEPE accelerometers for different cable capacitances and supply currents
Today in most applications IEPE accelerometers are preferred. However, charge mode accelerometers can be superior in some cases. The following table shows advantages and drawbacks of both sensor types.


IEPE Sensors
Charge Mode Sensors
Advantage
  • Fixed sensitivity regardless of cable length and cable quality
  • Low-impedance output can be transmitted over long cables in harsh environments
  • Inexpensive signal conditioners and cables
  • Intrinsic self-test function
  • Withstands better harsh conditions like dirt and humidity
  • No power supply required - ideal for battery powered equipment
  • No noise, highest resolution
  • Wide dynamic range
  • Higher operating temperatures
  • Smaller sensors possible
Disadvantage
  • Constant current excitation required (reduces battery operating hours)
  • Inherent noise source
  • Upper operating temperature limited to <120 °C
  • Limited cable length (< 10 m)
  • Special low noise cable required
  • Charge amplifier required
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发表于 2012-10-13 15:08 | 显示全部楼层
imglcao 发表于 2012-10-11 09:42
这个并未作深入的测试,因为单纯对供电来说,一般的恒流电路都完全能够满足使用而不会有影响,只是有些电 ...

谢谢!大致上已经明白了
发表于 2012-10-13 22:16 | 显示全部楼层
9V到24V不能升压,需要斩波器
发表于 2012-10-18 08:28 | 显示全部楼层
您好:
   我也在做这方面的东西,可以肯定的说,硬件肯定比软件块,可靠;我有现成的加速度转速度的原理图;
发表于 2012-10-18 15:21 | 显示全部楼层
guerhan 发表于 2012-10-13 22:16
9V到24V不能升压,需要斩波器

对电的东西不是太了解,但我们的恒流源一直是用9V电池供电,利用升压电路至20-24V/2-10mA给ICP传感器供电,至少18年前就是这样了。
发表于 2012-10-18 20:17 | 显示全部楼层
imglcao 发表于 2012-10-18 15:21
对电的东西不是太了解,但我们的恒流源一直是用9V电池供电,利用升压电路至20-24V/2-10mA给ICP传感器供电 ...

可以升压,只是要处理干净
发表于 2012-12-4 21:47 | 显示全部楼层
你可以去电子市场转转,买个恒流源
发表于 2012-12-8 12:33 | 显示全部楼层
本帖最后由 clhwyq 于 2012-12-8 12:37 编辑
imglcao 发表于 2012-10-10 08:16
一般来说,供电都是18-30V,电流2-20mA,只要供电是在这个区间的一个稳定值,对输出信号是没有任何影响的。 ...


如果供电功率不够,不但对输出信号的幅值有影响,对信号的频率也有非常大的影响,准确的说,就是测量出来的信号是错误的,不是真实信号。

另外,9V电是可以升到30V的。用加速度传感器通过硬件积分电路或者软件积分可以得到速度与位移,只是其随着时间的推迟其累积误差越来越大。
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