Sensitivity and range of piezoelectric accelerometers - Solutions - Huaqiang

inductance

The sensitivity of the sensor is one of the most basic indicators of the sensor. The magnitude of the sensitivity directly affects the sensor's measurement of the vibration signal. It is not difficult to understand that the sensitivity of the sensor should be determined according to the magnitude of the measured vibration (acceleration value), but since the piezoelectric acceleration sensor measures the acceleration value of the vibration, and the acceleration value and the frequency of the signal are squared under the same displacement amplitude condition. It is proportional, so the acceleration signals in different frequency bands vary greatly in size. The acceleration of the vibration of a large-scale structure may be quite small. For example, when the vibration displacement is 1 mm, the acceleration of the signal with a frequency of 1 Hz is only 0.04 m/s2 (0.004 g); however, the displacement of the high-frequency vibration is A 0.1mm signal with a frequency of 10kHz has an acceleration value of 4x105m/s2 (40000g). Therefore, although the piezoelectric accelerometer has a large measurement range, for the vibration signal used to measure the high and low frequencies, the sensitivity of the acceleration sensor should be adequately estimated. The most commonly used vibration measurement piezoelectric accelerometer sensitivity, voltage output type (IEPE type) is 50~100mV/g, and charge output type is 10~50pC/g.

The measurement range of the acceleration sensor is the maximum measurement that the sensor can measure within a certain nonlinear error range. The nonlinear error of the general-purpose piezoelectric acceleration sensor is mostly 1%. As a general rule, the higher the sensitivity, the smaller the measurement range, and the smaller the sensitivity, the larger the measurement range.

The measurement range of the IEPE voltage output type piezoelectric accelerometer is determined by the maximum allowable output signal voltage within the linear error range. The maximum output voltage value is typically ±5V. The maximum range of the sensor is obtained by scaling, which is equal to the ratio of the maximum output voltage to the sensitivity. It should be pointed out that the range of the IEPE piezoelectric sensor is limited by the magnitude of the nonlinear error and by the supply voltage and the bias voltage of the sensor. When the difference between the supply voltage and the bias voltage is less than the range voltage given by the sensor specification, the maximum output signal of the sensor is distorted.
Therefore, whether the bias voltage of the IEPE type acceleration sensor is stable or not affects not only the low frequency measurement but also the signal distortion; this phenomenon requires special attention when measuring the high and low temperature. When the built-in circuit of the sensor is unstable under non-room temperature conditions, The bias voltage of the sensor is likely to drift slowly and slowly, causing the measurement signal to flicker.

The charge output type measurement range is limited by the mechanical stiffness of the sensor. Under the same conditions, the maximum signal output of the sensing sensitive core subject to nonlinear nonlinearity of the mechanical elastic interval is much larger than that of the IEPE type sensor. Most of the values ​​are required. Determined by experiment. In general, when the sensitivity of the sensor is high, the mass of the sensitive core is larger, and the range of the sensor is relatively small. At the same time, because the mass is larger, the resonant frequency is lower, which makes it easier to excite the resonant signal of the sensitive core of the sensor. As a result, the resonant wave is superimposed on the signal to be measured to cause signal distortion output. Therefore, when selecting the maximum measurement range, the frequency composition of the signal under test and the natural resonance frequency of the sensor itself should also be considered to avoid the resonance component of the sensor. At the same time, there should be enough safety space on the range to ensure that the signal does not produce distortion.

The calibration method of the sensitivity of the accelerometer is usually determined by the comparison method. The ratio of the output of the sensor vibrated at a specific frequency (usually 159 Hz or 80 Hz) to the acceleration value read by the standard sensor is the sensitivity of the sensor. The sensitivity of the impact sensor is measured by measuring the output response of the sensor to a series of different impact acceleration values, obtaining the correspondence between the input impact acceleration value and the electric output of the sensor within the measurement range, and then obtaining and calculating by numerical calculation. The line with the smallest difference between the points, and the slope of this line is the impact sensitivity of the sensor.

The nonlinearity error of the impact sensor can be expressed in two ways: full-scale deviation or linear error by segmentation range. The former refers to the error percentage of the full-scale output of the sensor as the reference, that is, the error is calculated according to the percentage of the full scale regardless of the measurement value. The linear error of the segmentation range is calculated in the same way as the full-scale deviation, but the reference does not use the full scale but the segmentation range to calculate the error value. For example, if the measuring range is 20000g, if the full-scale deviation is 1%, the linear error is 200g in the full range; but when the sensor measures the linearity error by 5000g, 10000g, 20000g, the error is still 1%. The linearity error of the sensor in different three ranges is 50g, 100g, 200g.