What are the principles and characteristics of capacitive displacement sensors?
The principle of capacitance displacement sensor
capancdt capacitive displacement sensor is based on the principle of plate capacitance. The two poles of the capacitor are the sensor and the object being measured opposite to it. If there is a stable alternating current through the sensor, the output voltage of the alternating current will be proportional to the distance between the sensor and the measured object, so that distance information can be obtained by measuring the change in voltage.
The capacitive displacement sensor is a precision measuring instrument based on the principle of non-contact capacitive principle. It has the non-friction and non-destructive characteristics common to non-contact instruments. It also has a large signal-to-noise ratio, high sensitivity, low zero drift, and wide frequency response. , Small non-linearity, good accuracy and stability, strong anti-electromagnetic interference ability and convenient operation.
In practical applications, due to the unique design of the magnetic shielding ring, the capacitive sensor of German Miyrid can achieve almost perfect linear measurement. However, capacitive sensors require that the dielectric between the probe and the measured object must be uniform and constant. The measurement system is very sensitive to changes in the dielectric within the measurement range. The capacitive displacement sensor of German Miyridium can also be used for insulator measurement, because these insulators will change the dielectric constant in the measurement gap. Through the adjustment of the subsequent circuit, even if the insulator is measured, an almost linear signal output can be obtained. Due to the electromagnetic conversion process, capacitive sensors can measure all metals. The capacitance measurement system mainly measures the impedance value of the plate resistance, and the impedance value is proportional to the distance between the probe and the measured object.
The traditional capacitive sensor emits magnetic field lines from the side of the electrode. This magnetic field can cause erroneous measurement results. The capacitive sensor of German Miyridium has a grounding shielding ring, which can effectively reduce the side magnetic field and boundary effects, thereby obtaining more accurate measurement results. The magnetic field lines emitted from the ground shielding ring will not affect the measurement results.
High precision measurement
The capacitive measurement principle is one of several measurement principles with the highest accuracy. But the problem is that such a small measurement distance will cause the same small change in the measurement signal. In other words, only a small amount of electrons between the probe and the measured object can be used to show the change in distance. This means that if a small leakage current or parasitic current flows through the circuit from the probe to the controller, it will also affect the accuracy of the measurement results. Therefore, the cable between the probe and the controller requires a special double shielded cable. This special, fully enclosed RF cable guarantees high signal quality. The use of double-shielded cables and grounded magnetic shielding technology makes high-precision measurement possible.
The change in the conductivity of the measured object caused by the change of the ambient temperature has no effect on the measurement result. The capacitive measuring principle allows the sensor to be used even in fluctuating temperature environments. The capacitance sensor probe of German Miyridium has a very complicated internal structure. As a plate capacitor, the sensor can be installed on different mechanical structures according to the different requirements of customers.
The capaNCDT capacitive sensor of Miyrid Corporation in Germany is one of the most accurate displacement sensors in the world. The resolution can reach the nanometer level.
Mi Iridium’s capacitive sensor can be changed without recalibration. This undoubtedly greatly facilitates customers. This allows capacitance sensors and controllers of different ranges to be easily replaced without recalibration. The time to replace a sensor is only a few seconds, which is a huge advantage over most sensors on the market. German Miyridium also allows non-contact grounding of the measured object. If two-channel measurement is used at the same time, such as thickness measurement, the measurement results of the two channels must be synchronized. The object under test must be grounded. For capaNCDT series measuring systems, the grounding work is done by the controller. The process is done automatically.
Capacitive measurement principle characteristics:
Using the capacitive measurement principle, a clean and dry environment is required, otherwise the change in the dielectric constant of the material between the sensor probe and the measured object will affect the measurement result. We also recommend that the cable length between the probe and the controller is as short as possible at any time. For standard equipment, it is equipped with a preamplifier, and the cable length is set to 1m (depending on the choice of different modules, the longest can be up to 3m). If equipped with an external amplifier, the cable length between the probe and the controller can reach 20m.
Capacitive displacement sensors are generally used in applications requiring very high accuracy. They are used for measurement tasks such as vibration, oscillation, expansion, displacement, deflection and deformation. Therefore, capacitive displacement sensors are often used as quality assurance.
The latest type of capacitance displacement, the resolution can reach nanometer level. Due to its super temperature stability, capacitive sensors are the ideal choice under severe temperature fluctuations.
Application case: brake disc inspection
A typical case of capacitive displacement sensor is to measure the deformation of the brake disc under force. In order to get the measurement results closer to the real brake conditions, the brake discs must be tested under extreme conditions.
The brake disc rotates at a speed of 2,000 rpm and the temperature reaches 600°C. Only measurement methods with high measurement speed or cut-off frequency can not be affected by the changes in the magnetic and conductive properties of the measured object due to high temperature. The sensor probe also provides a particularly high resolution, because the deformation caused by the force of the brake disc is less than 100μm. The capacitive displacement sensor provided by German Miyridium can almost meet the needs of this application and is an ideal choice.
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