What signal sensor is HYDAC sensor
HYDAC sensor is a typical self generating sensor, which is based on the piezoelectric effect of certain crystals generating charges on their surface after being subjected to force as the conversion principle.
HYDAC sensor, also known as piezoelectric accelerometer. It also belongs to inertial sensors. It utilizes the piezoelectric effect of certain substances such as quartz crystals, and when the accelerometer is vibrated, the force exerted by the mass on the piezoelectric element also changes accordingly. When the measured vibration frequency is much lower than the natural frequency of the accelerometer, the change in force is proportional to the measured acceleration.
The upper limit frequency of the HYDAC sensor accelerometer depends on the resonance frequency in the amplitude frequency curve. Generally, for accelerometers with small damping (z<=0.1), if the upper limit frequency is set to 1/3 of the resonance frequency, the amplitude error can be guaranteed to be less than 1dB (i.e. 12%); If taken as 1/5 of the resonance frequency, it can ensure that the amplitude error is less than 0.5dB (i.e. 6%) and the phase shift is less than 30.
But the resonance frequency is related to the fixed condition of the accelerometer, and the amplitude frequency curve given by the accelerometer at the time of leaving the factory is obtained under the fixed condition of rigid connection. The actual fixing method often makes it difficult to achieve a rigid connection, resulting in a decrease in resonance frequency and upper limit frequency.
The fixing method of HYDAC sensor
The use of steel bolts for fixation is a method to achieve the factory resonance frequency. All bolts should not be screwed into the base screw holes to avoid deformation of the base and affecting the output of the accelerometer.
Applying a layer of silicone grease on the installation surface of HYDAC sensors can increase the connection reliability of uneven installation surfaces. When edge bolts and mica washers are needed to fix the accelerometer, but the washers should be as thin as possible. Using a layer of thin wax to stick the accelerometer onto the flat surface of the specimen can also be used in low-temperature (below 40 ℃) situations.
The handheld probe vibration measurement method is particularly convenient for multi-point testing, but the measurement error is large, the repeatability is poor, and the upper limit frequency is generally not higher than 1000Hz. Fixing the accelerometer with a magnet is convenient and mostly used in low-frequency measurements. This method can also connect the accelerometer to the edge of the specimen.
The fixing method of HYDAC sensors using rigid adhesive bolts or adhesives is also long. The resonance frequencies of a typical accelerometer using the various fixing methods mentioned above are approximately 31kHz for the steel bolt fixing method, 28kHz for the mica gasket, 29kHz for the wax coating method, and 2kHz for the handheld method,Magnetic fixation method at 7kHz.
The dimension of sensitivity is the ratio of the dimensions of the output and input quantities. For example, if a displacement sensor outputs a voltage change of 200mV when the displacement changes by 1mm, its sensitivity should be expressed as 200mV/mm.
When the output and input dimensions of the sensor are the same, sensitivity can be understood as amplification factor.
Improving sensitivity can achieve higher measurement accuracy. But the higher the sensitivity, the narrower the measurement range, and the poorer the stability.
resolution
Resolution refers to the ability of a sensor to perceive small changes in the measured data. That is to say, if the input quantity slowly changes from a non-zero value. When the input change value does not exceed a certain value, the output of the sensor will not change, that is, the sensor cannot distinguish the change in this input quantity. The output will only change when the input quantity changes beyond the resolution.
Usually, the resolution of each point in the full-scale range of sensors is not the same, so the large change value in the input quantity that can cause a step change in the output quantity in the full-scale range is commonly used as an indicator to measure the resolution. If the above indicators are expressed as a percentage of full scale, they are called resolution. There is a negative correlation between resolution and sensor stability.
Selection Principles
To carry out a specific measurement work, it is necessary to consider which principle of sensor to use, which requires analyzing multiple factors before determining. Because even when measuring the same physical quantity, there are multiple principle sensors available for selection. Which principle sensor is more suitable depends on the characteristics of the measured object and the conditions of the sensor, taking into account the following specific issues: the size of the measuring range; Requirements for sensor volume at the measured location; Is the measurement method contact or non-contact; The method of signal extraction, wired or non-contact measurement; The source of the sensor, whether it is produced or imported, whether it can withstand it, or self-developed. [6]
After considering the above issues, we can determine which type of sensor to choose, and then consider the specific indicators of the sensor.
Sensitivity selection
Usually, within the linear range of the sensor, it is desirable for the sensitivity of the sensor to be higher. Because only when the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial for signal processing. However, it should be noted that the sensitivity of the sensor is high, and external noise unrelated to the measured object is also easily mixed in, which can be amplified by the amplification system and affect the measurement accuracy. Therefore, it is required that the sensor itself should have a high signal-to-noise ratio and minimize the interference signals introduced from the outside.
The sensitivity of HYDAC sensors is directional. When the measured quantity is unidirectional and requires high directionality, sensors with lower sensitivity in other directions should be selected; If the measured vector is multidimensional, the smaller the cross sensitivity of the sensor, the better.
The frequency response characteristics of HYDAC sensors determine the frequency range being measured and must be maintained without distortion within the allowable frequency range. In fact, there is always a certain delay in the response of sensors, and it is hoped that the shorter the delay time, the better.
The higher the frequency response of the HYDAC sensor, the wider the measurable signal frequency range.
In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive errors.
linear range
The linear range of a sensor refers to the range where the output is proportional to the input. In theory, sensitivity remains constant within this range. The wider the linear range of the sensor, the larger its range and can ensure a certain measurement accuracy. When choosing a sensor, after determining the type of sensor, it is necessary to check whether its range meets the requirements.
However, in reality, no sensor can guarantee linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, sensors with small nonlinear errors can be approximated as linear within a certain range, which will bring great convenience to the measurement.