Principle and Application of Eddy Current Sensor

The basic working system of eddy current sensors consists of the measured object, probe, extension cable, and preamplifier. The preamplifier generates high-frequency oscillating current that flows into the probe coil through an extension cable. The coil generates an axial magnetic field. When the measured metal body approaches this magnetic field, eddy currents are generated on the surface of the measured metal (the strength of the eddy currents varies with the distance between the probe and the surface of the measured body), thereby causing the coil toQValue changes. When the distance is small, the eddy current effect is strong, and the coilQSmall value; When the distance is large, the eddy current effect is weak, and the coilQThe value is high. In practical applications, the coilQThe change in value is detected and amplified by the preamplifier, and converted into a change in voltage. Realize the mechanical displacement(gap)Convert the value into a voltage value.

2、 The influence of the tested material on the characteristics of eddy current sensors

Different tested objects have a significant impact on the characteristics of the sensor, and it is necessary to determine the material of the tested object when purchasing an eddy current sensor. Most manufacturers use45#Steel debugging before leaving the factory. Different materials of tested objects8mmThe probe sensor test is as follows.

3、 Characteristics of eddy current sensors

▲ Reliability:

=probe-30℃～150℃, extension cable in-30℃～200℃, the preamplifier is in-30℃～80℃； relative humidity95%Long term work in the environment will not cause damage. Selection of probe head bodyPPSEngineering plastics are molded through molds. Ensure that the probe has high strength and high temperature resistance(220℃)Corrosion resistance performance; Not easily damaged and will not corrode even when exposed to certain chemicals; Ensuring the reliability of the probe;

=Connect the probe signal to the coaxial cable used for the preamplifier. Coaxial cables should be selected with a wide temperature range(-55℃～200℃)Flame retardant and corrosion-resistant; High cable strength and good consistency of electrical characteristics (beneficial for reducing interchangeability errors);

=Industrial standard plug sockets are used for cable joints, which have low contact resistance and increased reliability;

=The output terminal of the preamplifier has fault tolerance and overload protection, so even if the wrong wire is connected, it will not cause damage to the circuit of the preamplifier;

=The preamplifier has lightning protection and suppresses power grid spikesMake the preamplifier safer.

▲ Temperature stability and accuracy:

=Relying on advanced compensation circuits to mitigate the effects of temperature changes in probe coils and cables(-22℃～120℃)Within the temperature range, the maximum deviation is less than ±5 % (Including linearity and sensitivity deviation)；

=Probe sensitivity error ±3%；

=Probe linear error ±1%；

=frequency responseDC～5 kHz

=resolution1um

4Technical parameters of eddy current displacement sensor

at room temperature25℃, tested material45#steel,power supply-24V±10%, load10KUnder the condition of Ω, the measured parameters are as follows:

5、 Application of eddy current sensors

Eddy current sensors can measure: shaft displacement, shaft vibration, speed, etc.

1 Axial displacement measurement with an accuracy of1%The output can be selected from voltage output and current output. Install as shown in the following figure.

2Shaft vibration measurement with an accuracy of5%Install the following image.

3Speed measurement, accuracy0.1%Install as shown in the following figure