Capacitive Sensor Measuring Principle Capacitive Measuring Principle

For general acoustic emission applications, the signal frequency band range is mostly between 25kHz and 750kHz, so resonant sensors are more suitable. Resonant narrowband sensors with a general broadband frequency of 150kHz are commonly used for metal materials and other applications; For acoustic emission signals such as corrosion and leakage, resonant sensors with a resonant frequency of 40kHz are commonly used; Due to the relatively low response sensitivity of wideband sensors in a wide frequency band, wideband sensors are selected for spectrum analysis. Qingcheng acoustic emission sensor is made of high-quality stainless steel material, and the overall shielding design can effectively reduce interference; It is suitable for bridge wire fracture monitoring, valve pipeline leakage monitoring, tool wear monitoring, wind power equipment monitoring, rotating equipment acoustic emission monitoring, structural parts damage monitoring, storage tank floor acoustic emission monitoring.

Commonly used thermocouples are divided into *** and cheap metals.

There are.

Platinum rhodium 10 - platinum.

Platinum rhodium-13 - platinum.

Platinum rhodium-30 - platinum 6

There are cheap metals.

Copper - Constantan.

Iron - Constantan.

Nickel - copper-nickel.

Nickel branding - nickel-silicon.

The equilibrium condition of the tributary bridge: the product of the resistors of the two opposing resistors is equal.

Static indicators: precision, accuracy, precision.

It's as if I've never heard of dynamic indicators.

Mohr elements have not heard of it.

Looks like there's a Hall sensor.

Its main material is magnets.

Piezoelectric sensors: Sensors based on the piezoelectric effect. It is a self-generating and electromechanical conversion sensor.

Its sensitive elements are made of piezoelectric materials. When a piezoelectric material is stressed, an electric charge is generated on the surface. This charge is amplified and converted by the charge amplifier and the measuring circuit to become the output of electricity proportional to the external force.

Piezoelectric sensors are used to measure forces and non-electrophysical quantities that can be converted into forces, such as pressure, acceleration, etc. (see Piezoelectric Pressure Sensors, Accelerometers). Its advantages are frequency bandwidth, high sensitivity, high signal-to-noise ratio, simple structure, reliable operation and light weight. The disadvantage is that some piezoelectric materials require moisture protection measures and the DC response of the output is poor, requiring a high input impedance circuit or charge amplifier to overcome this drawback.

The emergence of supporting instruments and low-noise, small-capacitance, and high-insulation resistance cables makes the use of piezoelectric sensors more convenient. It is widely used in engineering mechanics, biomedicine, electroacoustics and other technical fields.

Strain sensor: Strain sensor is a widely used one at home and abroad, it is a resistance strain gauge as a conversion element, the non-electric such as: force, pressure, displacement, acceleration, torque and other parameters into electricity.

Photoelectric sensor: A sensor that converts an optical signal into an electrical signal.

Thermoelectric sensor: A sensor that converts a heat signal into an electrical signal.

1.The experimental principle of capacitor discharge measurement capacitance is used.

After the capacitor is charged, the relationship between the charge Q and the voltage U and capacitance C between the two plates satisfies Qcu. U can be measured by DC voltmeter, and Q can be measured by capacitor discharge. Make the capacitor discharge through high resistance, the discharge current decreases with the voltage drop between the two plates of the capacitor, and the discharge current value at different times is measured until i 0, and the curve of the discharge current i with time is made, and the area under the curve is equal to the charge carried by the capacitor.

The capacitance of the capacitor can be found from c q u.

2.Capacitance is measured using the discharge time ratio.

The measurement principle is to connect the measured capacitance and the reference capacitance to the same resistor to form an RC network. By measuring the ratio of the discharge time of the two capacitors, the capacitance value of the capacitor under test can be calculated. Measurements range from pf (10-12F) to dozens of NF (10-9F) and in parasitic capacitance.

It has great advantages in terms of suppression and temperature stability.

3.Utilize a microcontroller.

Pulse measurement measures the time constant.

RC then calculates the capacitance.

The measurement principle is to connect the measured capacitance and resistance in series to form an RC network, and then you can use this time constant to get an oscillator, adjust the waveform of the oscillation signal and then start counting the pulse value, the possible period is t=a0 rc, a0 is a constant.

Capacitive sensors work as follows:

Capacitive sensor is also often called capacitive level meter, the capacitance detection element of capacitive level meter is based on the principle of cylindrical capacitor, the capacitor is composed of two insulated coaxial cylindrical plates inner electrode and outer electrode, between the two cylinders charged with the electrolyte of the dielectric constant, the capacitance between the two cylinders is the length of the overlapping part of the two cylinders.

d is the diameter of the outer cylinder electrode. d is the diameter of the inner cylinder electrode; e is the dielectric constant of the intermediate medium. In the actual measurement, d, d, e are basically unchanged, so the measurement of c can know the level of the liquid, which is also one of the reasons why the capacitive sensor has the characteristics of easy to use, simple structure and high sensitivity, and low price.

Capacitive sensors use various types of capacitors as sensing elements, and the capacitance of the capacitor changes due to the change to be measured, and the change in capacitance can be converted into an electrical signal output through the measurement circuit. By measuring the magnitude of the electrical signal, it is possible to determine the size to be measured. This is how capacitive sensors basically work.

An introduction to capacitive sensors

Capacitive sensors typically use a round or metallized film as one of the electrodes of the capacitor. Capacitive pressure sensors belong to the capacitive sensors with pole distance variation, which can be divided into single capacitive pressure sensors and differential capacitive pressure sensors.

Single capacitive sensor

It consists of a round thin film with fixed electrodes. The diaphragm can be made by plating a metal layer of plastic. This type is suitable for measuring low pressures and has a high overload capacity.

Single-capacitive pressure sensors with piston moving diaphragms can also be used to measure high pressures. This type reduces the direct pressure area of the diaphragm to allow for a thinner diaphragm to increase sensitivity.

It is also packaged as a whole with various compensation and protection parts and amplification circuits to improve immunity to interference. This sensor is suitable for measuring dynamic high pressures and telemetry of aircraft. Single-capacitive pressure sensors are also available in microphone type (i.e., microphone type) and stethoscope type.

Differential capacitive sensors

Its pressurized diaphragm electrode is located between two fixed electrodes and constitutes two capacitors.

How do capacitive sensors work? What items does it detect?

Capacitive sensors use various types of capacitors as sensing elements to convert measured physical or mechanical quantities into capacitance changes, which is actually a capacitor with variable parameter balance. Capacitive sensors are widely used for the measurement of displacement, angle, vibration, velocity, pressure, composition analysis, media characteristics, etc. The most commonly used are parallel plate capacitors or cylindrical capacitors.

Capacitive sensor is also often called capacitive level meter, the capacitance detection element of capacitive level sensor is based on the principle of cylindrical capacitor, the capacitor is composed of two insulated coaxial cylindrical plates inner electrode and outer electrode, between the two cylinders charged with an electrolyte with dielectric constant e, the capacitance between the two cylinders is c = 2 el lnd d, where l is the length of the overlapping part of the two cylinders.

d is the diameter of the outer cylinder electrode. d is the diameter of the inner tube electrode, and e is the dielectric constant of the intermediate medium. In the actual measurement, d, d, e are basically unchanged, so the measurement of c can know the level of the liquid, which is also one of the reasons why the capacitive sensor has the characteristics of easy to use, simple structure and high sensitivity, and low price.

Measure the amount of charge stored on the plate, or dielectric strength. Check the capacity, choose the range according to the different capacity, use two meter pens to lap the two feet of the capacitor during the test, the watch needle has a certain value, and then return to the infinity bit, change the meter pen and try again, this time the pointer swings slightly off, and then back to infinity, indicating that the capacitance is not damaged, if it cannot return to infinity, it means leakage, if it means that the needle does not swing, it means that the internal circuit or no capacity. Then, compare the capacitance with the same gauge and virtual spike grid to see if the capacity is reduced.

<>1. The capacitance sensor is also known as the capacitance level meter, and its capacitance detection element works based on the principle of cylindrical capacitor, the cylindrical capacitor is mainly composed of two coaxial cylindrical plates that are insulated from each other, and the medium is filled between the two plates, then the capacity of the capacitor is c=2 el lnd d, wherein, represents the dielectric constant of the medium between the two plates, l represents the length of the two plates that coincide with each other, d represents the diameter of the outer cylindrical plate, and d represents the diameter of the inner cylindrical plate. Since the three parameters of d, d, and e do not change when measured under fixed conditions, the level height can be known according to the measured capacitance.

2. Capacitive sensors have certain advantages over resistive sensors and inductive sensors, but they are not perfect, and they also have shortcomings

3. Advantages: Cheap, affordable; High sensitivity and accuracy; Simple structure; It can also be applied in harsh environments; Good temperature stability; with an averaging effect; Good dynamic responsiveness; High overload capacity.

4. Disadvantages: output is non-linear; The sensitivity and measurement accuracy of parasitic capacitance and distributed capacitance are easily affected and unstable; The connection circuit is more complex.