张家港ML33 Eddy Current Displacement Sensor

Working principle:

The working principle of eddy current sensor system is eddy current effect, which belongs to an inductive measurement principle. The eddy current effect results from the energy of the oscillating circuit. Eddy currents need to be formed in conductive materials. An alternating current is introduced into the inner coil of the sensor probe to create a magnetic field around the probe coil. If you put a conductor in this field, according to Faraday's law of electromagnetic induction, eddy currents will be excited within the conductor. According to Lenz's law, the direction of the eddy current's magnetic field is opposite to the coil's magnetic field, and this will change the impedance value of the coil inside the probe. The change in this impedance value is directly related to the distance between the coil and the object being measured. After the sensor probe is connected to the controller, the controller can obtain the variation of voltage value from the sensor probe and calculate the corresponding distance value based on it. The principle of eddy current measurement can measure all conductive materials. Because the eddy current can penetrate the insulator, even if the surface is covered with the metal material of the insulator, it can also be used as the object of the eddy current sensor. The unique coil winding design can not only realize the compact shape of the sensor, but also meet the requirements of its operation in the high temperature measurement environment.

Scope of Application:

By measuring the relative position of the metal measured body and the probe end, the eddy current displacement sensor induces and processes the corresponding electrical signal output. Sensor can work reliably for a long time, high sensitivity, strong anti-interference ability, non-contact measurement, fast response speed is not affected by oil and water and other media, in large rotating machinery axis displacement, axis vibration, axis speed and other parameters of the long-term real-time monitoring is widely used. And has been extended to satellite launch, material identification, weighing measurement, metal plate thickness measurement, material shape variables and other applications.

Technical parameter：

Connection definition：

Product size：

The ML33 sensor system consists of a probe, preprocessor, cable, and accessories.

1、Eddy current sensor probe

Standard probe installation size:

Usually the probe consists of a coil, a head, a shell, a high-frequency cable and a high-frequency connector.

In the production process, the head body of the probe is generally made of high temperature resistant PPS engineering plastics, and the coil is sealed by "secondary injection molding". The probe can work reliably in harsh environment. Because the diameter of the head coil determines the linear range of the sensor system, we usually use the external diameter of the head body to classify and characterize each type of probe. In general, the linear range of the sensor system is roughly 1/2 ~ 1/4 times of the diameter of the probe head. The sensor probe of ML33 series is shown in the figure (standard type) :

The probe housing is used to connect and secure the probe head and is used as a clamping structure for the probe installation. The shell is usually made of brass nickel-plated process, engraved with standard threads and equipped with lock nuts. In order to adapt to different applications and installation occasions, the probe housing has different forms and different threads and dimensions.

Mounting size of countersunk probe:

Installation size of square probe:

Round probe mounting size:

Eddy current sensor preprocessor

The preprocessor is the signal processing center of the whole sensor system. On the one hand, the preprocessor provides high frequency AC excitation current to the probe coil to make the probe work; On the other hand, the preprocessor induces the gap change between the probe head body and the metal conductor in front of the head body through a special circuit. After processing by the preprocessor, the voltage or current output signal changes with the linear change of the gap.

Outline size of ML33 series preprocessor:

Product naming rules

1、Probe

●  A □□:Probe range code selection

▼   Probe code classification 

●  B□□ :No thread length option

  he threaded part of the probe is to facilitate installation, reduce invalid thread length, and make screwing bolts faster

▼Metric threaded probe

● C □□ Shell length selection

The length of the probe shell depends on the use of the site, in order to ensure the measurement accuracy, avoid the vibration of the probe rod to bring measurement interference, it is recommended not to use more than 300mm long shell length; When necessary, a mounting attachment for strengthening the probe rod should be attached.

▼Metric shell length

 

● D □□：Probe shape structure selection 

   This option does not represent the standard probe structure; C is for countersunk structure. Choose F to represent the square probe structure, choose Y to represent the circular probe structure.

Preprocessor naming rules

● A □    Preamplifier shell selection

      A:  Type A shell

        B:  Type B shell

        R:  RS485 exclusive use

● B □    Output mode selection  

A: Represents the current 4-20ma output    +24 V DC power supply 

V1-1: Represents a voltage of 0-5v output      ±15V DC power supply

V1-2: Represents a voltage of 0-5v output      +12V DC

V1-3: Represents a voltage of 0-5v output      +24V DC power supply

 V2-1: Represents a voltage of 0-10v output    ±15V DC power supply

V2-2: Represents a voltage of 0-10v output    + 12V DC power supply

V2-3: Represents a voltage of 0-10v output       + 24V DC power supply

 R: Represents RS485 output             +12V DC power supply

Installation of probe

When installation the probe, you should pay attention to the following issues:

口The distance between the probe        口Distance between probe and mounting surface

口Mounting bracket selection             口Probe mounting clearance

口Installation of cable with probe          口Sealing and insulation of cable adapters

口Corrosion resistance of the probe        口High pressure environment of probe

●The distance between the probes

When the probe head coil through the current, there will be alternating magnetic field around the head, so pay attention to the installation of the two probes can not be too close, otherwise the two probes will interfere with each other through the magnetic field (as shown in the following figure between the probe distance), the output signal superimposed on the two probes of the difference frequency signal, resulting in distortion of the measurement results, This is called adjacent interference. Factors related to the exclusion of adjacent interference: the shape of the measured body, the diameter of the probe head and the installation mode. The minimum distance between probes in general is shown in the table below.

●Distance between probe head and mounting surface

The alternating magnetic field emitted by the head of the probe has a certain radial and transverse diffusion. Therefore, during installation, it is necessary to consider the influence of metal conductor materials on the installation surface, and ensure that the head of the probe is not less than a certain distance from the installation surface. The engineering plastic head body should be completely exposed to the installation surface, otherwise the installation surface should be processed into a flat bottom hole or chamfer, as shown in the following figure.

1. Select the sensor according to the range of the measuring position, the environment and size of the installation space, and the characteristics of the measured body material, and check whether the appearance of each part of the sensor is intact and whether each part is supporting (such as whether the diameter of the probe is consistent with the diameter of the supporting probe stipulated in the preprocessor type number, whether the cable length of the probe is in line with the requirements of the cable length of the preprocessor, etc.). Sensors ordered in complete sets are usually provided with a data verification sheet when leaving the factory, which indicates the model and number of each part of the sensor for matching calibration, so that users can check with the marks on the product according to it. Then, specific marks are made on the probe and preprocessor of the sensor respectively.

2. The probe cable connector is connected with the internal circuit, and does not have the sealing property. In order to avoid contact between the joint and the casing and to strengthen the tightness, the joint should be heated and shrink-wrapped with a heat shrink sleeve. This can also play a role in preventing the joint from loosening. Do not use sticky electrical tape to insulate the joint, as oil mist can dissolve the adhesive on the tape and contaminate the joint.

3. Once the length of the probe cable is selected, it can not be shortened or lengthened at will when in use. Too long cable can not be cut at will, otherwise it may cause the sensor to be seriously out of tolerance or not work normally. The probe cable length shall be the same as the cable length required by the preprocessor. Except for special specifications.
4, connect all parts of the sensor, power check the sensor, if out of tolerance, it needs to be recalibrated. During inspection, special attention should be paid to whether the material of the test piece is consistent with the material of the measured body or has similar composition.
5. If the supporting installation bracket has not been ordered, the appropriate installation bracket should be processed by itself. The external installation of the probe bracket is more complex, generally should be ordered.
6, in the frame processing support installation bracket of the screw hole, the internal installation of the probe bracket generally need two screw holes for fastening, the external installation of the probe is generally in the shell processing with threaded through holes.

7. Tighten and install the probe bracket. If the probe is installed externally, the probe should be first secured to the bracket, and then the bracket is screwed into the mounting hole.
8, adjust the probe installation clearance. The initial installation clearance of the probe has different requirements for different purposes.

9. Tighten and install the probe. For the internal installation of the probe, if the Angle bracket is used, the back is tightened with two nuts, and the clamping block is locked with fastening screws; For external mounting probes, tighten external mounting brackets. Fastening screws and nuts should be equipped with spring washers to prevent loosening.

Probe installation

The requirements of the working environment of the transmitter is much stricter than that of the probe, and it is usually installed away from the danger zone. The surrounding environment should be free of corrosive gases, dry, small vibration, and the ambient temperature is not much different from room temperature. Installation beside the machine, in order to ensure the transmitter safe and reliable work, it is necessary to use a special installation box. In order to prevent the interference caused by different ground potentials, it is necessary to use single point grounding.

Matters need attention

1.Requirements for probe mounting clearance