ML33-RG High temperature resistant type eddy current displacement sensor

I. Principle of ML33-RG high temperature resistant type eddy current displacement sensor:

Eddy current sensor systems work on the eddy current effect, which is an inductive measuring principle. The eddy current effect originates from the energy of an oscillating circuit. The eddy currents need to be formed in a conductive material. By introducing an alternating current into the coil inside the sensor probe, a magnetic field is formed around the probe coil. If a conductor is placed into this magnetic field, eddy currents are excited in the conductor according to Faraday's law of electromagnetic induction. According to Franz's law, the magnetic field of the eddy currents is in the opposite direction of the magnetic field of the coil, and this changes the impedance of the coil inside the probe. This change in impedance is directly related to the distance from the coil to the object being measured. After the sensor probe is connected to the controller, the controller can obtain the change in voltage value from the sensor probe and use this as a basis for calculating the corresponding distance value, the eddy current measurement principle can measure all conductive materials.
Since eddy currents can penetrate insulators, even metallic materials covered with insulators can be used as measurement objects for eddy current sensors. The unique coil winding design enables the sensor to operate in high-temperature measurement environments while maintaining a compact form factor.

2. ML33-RG high temperature resistant type eddy current displacement sensor application areas:By measuring the relative position of the metal body to be measured and the probe end, eddy current displacement sensor sensing and processing into the corresponding electrical signal output. The sensor can work reliably for a long time, high sensitivity, strong anti-interference ability, non-contact measurement, fast response speed is not subject to the influence of oil and water and other media, in the large-scale rotating machinery, such as shaft displacement, shaft vibration, shaft speed and other parameters of long-term real-time monitoring is widely used, and has been extended to the satellite launch, material identification, weighing measurement, metal plate thickness measurement, material deformation and other application areas.
3. ML33-RG high temperature resistant type eddy current displacement sensor technical parameters:

4.ML33-RG high temperature resistant type eddy current displacement sensor wiring:
The sensor has five contacts: positive power (brown), power ground (black), RS485A (blue), RS485B (white), and case ground (shielded).
5. ML33-RG high temperature resistant type eddy current displacement sensor installation dimensions:
The ML33 sensor system consists of probes, proximitor, cables, and accessories.

1. Eddy current probe:

Usually the probe consists of a coil, head, shell, high-frequency cable, high-frequency connector. In the production process, the probe head body is generally used in high temperature PPS engineering plastics, through the ‘secondary injection’ moulding will be sealed coil. So that the probe can work reliably in harsh environments. As the coil diameter of the head body to determine the linear range of the sensor system, so we usually use the external diameter of the head body to classify and characterise the various types of probes, in general, the linear range of the sensor system is roughly 1/2 to 1/4 times the diameter of the head of the probe.ML33 series sensors probes are shown in the table:

Probe housings are used to connect and secure the probe head and are used as a clamping structure when the probe is mounted. The housings are generally made of 304 stainless steel with standard threads and locking nuts. In order to adapt to different applications and installations, probe housings are available in different forms and with different threads and dimensions.

2. Proximitor:

The proximitor is the signal processing centre of the whole sensor system. On the one hand, the preamplifier for the probe coil to provide high-frequency AC excitation current to make the probe work; on the other hand, the preamplifier through a special circuit senses the probe head body and the head body in front of the metal conductor of the gap changes, through the preamplifier processing, resulting in the gap with the linear changes in the output signal.

ML33-RG series proximitor outline dimensional drawing  

Probe selection rulers

●  A □□:Probe range code selection

▼   Probe code classification 

●  B□□ :No thread length option

  The 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

● 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

6. Installation and use:

Probe installation

● When mounting the probes, you should pay attention to the following issues.

□ Distance between each probe of the port            □Distance between the port probe and the mounting surface

□Selection of mounting bracket                               □Mouth probe mounting clearance

□Installation of the cable with the probe                 □Sealing and insulation of the cable adapter of the port

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

● Distance between probes
When the current is passed through the coil of the probe head, an alternating magnetic field will be generated around the head, so when installing the two probes, it should be noted that the installation distance between the two probes should not be too close, otherwise the two probes will interfere with each other through the magnetic field (as shown in the following figure of the distance between the probes), and the output signal iterated on the two probes of the differential signal, resulting in a distortion of the results of the measurements, which is a case we call the neighbourhood of the interference. Factors related to the elimination of neighbouring interference are: the shape of the measured body, the head diameter of the probes, and the mounting method. Typically, the * minimum distance between the probes is shown in the table below.

The alternating magnetic field emitted by the head of the probe has a certain diffusion in both radial and lateral directions. Therefore, in the installation, it is necessary to consider the influence of the metal conductor material of the mounting surface, should ensure that the probe head and the mounting surface is not less than a certain distance between the head body of engineering plastics should be completely exposed to the mounting surface, otherwise, the mounting surface should be machined into a flat-bottomed hole or chamfered, as shown in the figure below.

1, according to the measuring part of the range, the environment and size of the installation space, the measured body material and other characteristics of the selected sensor, and check the sensor parts of the appearance is intact, whether the parts are matching (such as the probe diameter and preamplifier models specified in the matching probe diameter is consistent with the length of the probe cable is consistent with the preamplifier on the cable length requirements, etc.). Usually ordered in sets of sensors, in the factory to provide a data calibration sheet, the calibration sheet indicates the matching calibration of the sensor parts of the model, number, the user can be based on this and the mark on the product check. Then in the sensor probe, preamplifier were specific marking.

2, the probe cable connector is connected to the internal circuit, and does not have a sealed. In order to avoid contact between the connector and the chassis as well as to strengthen the sealing, heat-shrinkable tubing should be used to heat-shrink wrapped tightly around the connector. This also serves to prevent the connector from loosening. Do not use sticky electrical tape to insulate the joints, as oil mist will dissolve the adhesive on the tape and contaminate the joints.  

3, probe cable length once selected, in use can not be arbitrarily shortened or lengthened, too long cable can not be arbitrarily cut, otherwise it may cause the sensor serious over-performance or can not work properly. Probe cable length should be consistent with the cable length required by the preamplifier. Unless special specifications.

4, the sensor parts of the coupling, power on the sensor check, if the super poor, then need to be recalibrated. Check should pay special attention to the calibration test piece material is consistent with the measured body material or has a similar composition.

5、If the matching mounting bracket is not ordered, you should process a suitable mounting bracket by yourself. External mounting probe bracket is more complicated, generally should be ordered.

6, in the base of the processing support mounting bracket screw holes, internal mounting probe bracket generally need two screw holes for fastening, external mounting probe is generally in the housing processing with threaded through holes.

7、Fasten the mounting probe bracket. If the probe is mounted externally, the probe should be fastened to the bracket first, and then screw the bracket into the mounting holes.

8、Adjust the probe mounting clearance. The initial mounting clearance of the probe has different requirements for different applications.

9、Fasten the mounting probe. For internal installation of the probe, if the angle bracket is used with two nuts back to tighten, the use of clamping block is locked with the fastening screws; for external installation of the probe, fasten the external mounting bracket. Fastening screws and nuts should be added spring washers to prevent loosening.

Installation of the preamplifier:

The requirements of the transmitter on the working environment are much stricter than the probe, usually it will be installed far away from the hazardous area, its surrounding environment should be free of corrosive gases, dry, low vibration, the ambient temperature is not much different from the room temperature. In order to ensure that the transmitter works safely and reliably, it is necessary to use a special mounting box for installation next to the machine. In order to prevent interference caused by different ground potentials, a single point of grounding must be used.