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Eddy Current Displacement Sensor
Product Name:ML33 Series Eddy Current Displacement Sensor
Product Summary:

ML33 series eddy current displacement sensor performance indicators are close to or close to the United States Bentley (BN) 3300 series level.

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Chapter One   Eddy current displacement sensor

              

                   Section 1   Introduction

  ★The Working Principle of the System

       The working principle of the sensor system is the eddy current effect. When connecting the sensor power supply system, in the pre reactor will produce a high frequency current signal, the signal sent to the probe through the cable head, H1 in the alternating magnetic field generated around the head, if in the range of H1 in magnetic field is not close to the metal conductor material is transmitted to a range of energy will be released; on the contrary, if a metal conductor material close to the head of the probe, the alternating magnetic field H 1 will be generated on the surface of the conductor eddy current field, the electric vortex flow field will produce a direction with H 1 opposite magnetic field H 2. Due to the reaction of H 2, the amplitude and phase of the high frequency current of the probe coil will be changed. This change is not only related with the eddy current effect, which was related to the static magnetic effect with metal conductor conductivity, permeability, coil geometry, geometric parameters, excitation current and frequency coil to the metal conductor distance and so on. The metal conductor is assumed to be homogeneous and its performance is linear and isotropic. The physical properties of the metal conductor system can usually be made of metal conductor permeability, conductivity, size sigma factor R, and coil. The distance of the metal conductor, the excitation current intensity I and the frequency of the coil are described. The available functions of Z=F coil impedance (mu, sigma, R, I, w) to express. If the control, R, mu, sigma delta, Omega, I constant, then the impedance of the Z becomes single value function from the Delta, by the Maxwell formula, we can obtain the function is a nonlinear function, the curve is "S" curve, in a certain range can be approximated as a linear function

 

                                          

  ★Application Range of Eddy Current Displacement Sensor

By measuring the relative position of the metal probe and the probe end, the eddy current displacement sensor is induced and processed into a corresponding electrical signal output. The sensor can work reliably for a long time, high sensitivity, strong anti-interference ability, non-contact measurement, response speed, speed effect is not affected by the oil and water, are widely used in real-time monitoring of parameters in long axis displacement, large rotating machinery shaft vibration, shaft speed, and is extended to the satellite launch, material identification, weighing measurement, metal plate thickness measurement, material deformation and other applications.

 

  ★Complete Sensor System Components

  A complete set of sensor system mainly includes the probe, the front device and accessories. System components are shown in the following figure:

 

 

                     

 

 

 ★Compatibility With Similar Products

   ML33 series eddy current displacement sensor performance indicators are close to or close to the United States Bentley (BN) 3300 series level, better than the domestic similar products.

 

         Section 2  The Influence of the Machined Surface Condition on the Measured Results

The surface finish of the probe is also affected by the measured results! The measured body surface is not smooth, in the measurement of actual application will bring additional errors, especially for vibration measurement, vibration signal superposition error signal and the actual, and it is difficult to separate in electric, so the measured surface should be smooth, there should be no scratches, holes, bulge or groove the defect (for specially for the key phase detector, speed measurement settings of the boss or the groove except). According to the API670 standard recommended values for vibration by measuring the surface roughness of Ra in 0.4um ~ 0.8um, if you can not meet the need of development, grinding or polishing surface to be measured; for displacement measurement, the filtering effect indicator or average effect, can be slightly relaxed (general surface roughness Ra is less than 0.4um ~ 1.6um).

 

           Section 3  The Influence of Measuring Material on Measurement Results

     The sensor characteristics (here sensitivity) and measured the resistivity and permeability of. When the measured body for magnetic materials (such as ordinary steel, steel structure, etc.) due to the magnetic effect and eddy current effects exist at the same time, and the magnetic effect and eddy current effect on the contrary, in part to offset the effect of eddy current, so that the sensor sensitivity is reduced; and when the measured object is non-magnetic or weakly magnetic materials (such as copper guide aluminum, alloy steel, etc.), due to relatively weak magnetic effect, eddy current effect is stronger, so the sensor sensitivity is high.

        Copper:                    14.9V/mm

        Aluminum:                    14.0V/mm

      Stainless Steel(1Cr18Ni9Ti):    10.4V/mm

        45 Steel:                8.2V/mm

        40CrMo Steel:              8.0V/mm(Factory Calibration Material)

 

Unless in order for the special instructions, usually at the factory before the sensor system using 40CrMo materials for calibration specimen material was measured and it only with the series, the characteristic equation and 40CrMo similar to 40CrMo; when the material and components of the measured object is great, it must be re calibration. Otherwise it may cause great error.

※Because most of the steam turbine shaft, blower etc. equipment is made of 40CrMo material or with similar material, so the sensor system with 40CrMo material factory calibration, suitable for most of the measured object.

The influence of residual magnetic effect on measured results

  The residual magnetic effect formed during the processing of the materials, and the quenching is uneven, uneven hardness, uneven crystal structure will affect the sensor characteristics, API670 recommended the measured surface residual magnetism is not more than 0.5 micro tesla. When higher measurement accuracy is required, the actual measured body should be calibrated.

The influence of the coating on the measured surface

   Different coating materials, the sensitivity of the sensor will be different. If the coating is uniform, and the thickness is greater than the depth of vortex penetration. The sensor is calibrated according to the coating material, which will not affect the use.

                   

 

        Section 4   Effect of High Frequency Coaxial Cable

   High frequency coaxial cable is one of the main factors that affect the electrical performance of eddy current sensor. Because the sensor works in the high frequency state (the oscillation frequency is about 1MHZ), the frequency attenuation, the temperature characteristic, the impedance, the length and so on of the high frequency coaxial cable are all the factors that influence the performance of the sensor! For this reason, the high frequency coaxial cable of eddy current displacement sensor cannot be interchanged!

   

         Section 5  Influence of External Magnetic Field

  Eddy current sensor is a kind of inductive sensor, and its main function is the eddy current effect, so the influence of external magnetic field should be considered in engineering application! Strong external magnetic field will certainly affect the performance of the sensor.

     1、As for the static magnetic field, the direction of the magnetic field and the eddy current magnetic field may be present in a variety of situations because of the static magnetic field intensity. Once the direction of the external static magnetic field is determined, the interference of the eddy current field is also certain. Therefore, in practical engineering applications, the influence of the static magnetic field can be measured through the field test to measure the sensitivity of the sensor.

     2、For the external alternating magnetic field, such as frequent starting large exciter, large motor, start the machine, the magnetic field intensity and direction may not be a fixed value, thus resulting in the amount of the eddy current sensor range far down the alternating magnetic field, or take measures to shield the magnetic field to produce a minimal effect.

Chapter Two  ML33 Electric Eddy Current Displacement Sensor

                                    Section 1  Product description

1、Probe

      Usually, the probe is composed of a coil, a head, a shell, a high-frequency cable and a high frequency connector. The typical structure is shown in figure 2.

           

                    figure 2  Probe typical structure

 

 

       In the production process, the probe head body generally uses high temperature resistant PPS engineering plastic or high temperature resistant PTFE, through the "two injection molding" forming the coil seal. The probe can work reliably in harsh environments. Because of the linear range head coil diameter determines the sensor system, so we usually use external diameter to head the classification and characterization of various types of probes, linear range sensor system in general is roughly the probe head diameter of 1/2 ~ 1/4 times. The ML33 series sensor consists of phi 5, Phi 8, Phi 11, Phi 18, Phi 25, Phi 50, Phi 60 7 total head diameter is shown in figure:

 

The probe shell is used for connecting and fixing the probe head, and the clamping structure is used as the probe. The shell is generally made of stainless steel, the general standard is engraved with thread, and has a locking nut. In order to adapt to different applications and installation occasions, the probe shell with different forms and different thread and size specifications

2、Proximitor

   The former is the signal processing center of the whole sensor system. On the one hand, the proximitor to provide high frequency AC coil excitation current of the probe; on the other hand, preamplifier circuit of induction by special clearance change probe head body and the head in front of the body of the metal conductor, after processing the proximitor, with occasional linear change of the output voltage or current signal.

There are two kinds of structure of ML33 series pre - connector

      A shell

   

 

B shell

The preamplifier circuit is designed with fault tolerance; the power supply is connected with the fault protection and output short circuit protection; the power supply end, the common terminal (signal ground) and the output terminal can not be damaged.

The front circuit in addition to individual calibration for the components, other components are encapsulated by epoxy resin, which can provide anti vibration, moisture-proof performance of the preamplifier.

3. Product marking

   A complete set of eddy current sensors shall include the front, the probe and the extension cable. The eddy current sensor should be corresponding and supporting the use of, not wrong; in the factory calibration single proximitor, to complete the probe and extension cable is numbered, proximitor, and probe the user can quickly find a complete extension of the corresponding sensor cable.

   *The proximitor type and serial number on the surface of the proximitor shell eye-catching.

   *A transparent heat shrinkable sleeve probe and extension cable type and sealing joints in high frequency near the serial number on the cable.

   The user can according to the model indicated that the factory calibration on the list and the serial number, the control on the product label, the system supporting the calibration according to the factory. General requirements for calibration check in sensor before use, especially when the conditions of use and factory calibration conditions are not the same, especially the measured materials and factory calibration of single material does not indicate that calibration must be re calibrated at the same time.

Standard accessory

1. Each standard mounting probe is equipped with 2 nuts (six angle thin nut GB6173-86, material 1Cr18Ni9Ti, thread specification and probe thread specification) of the 2 spring washers

2.  The heat shrinkable sleeve: specification of each probe with a diameter of 8 mm long, transparent, 200mm (for the number and protection adapter).

             3.   Each front is equipped with 4 M4X8 six - angle screws.

Other relevant information

     1、Product certification and factory inspection certificate.

     2、Use manual

     3、Packing list (one copy)

 

              Section 2    Acceptance and storage

One: Check Before Acceptance

1、Remove all parts of the system from the box. Check for damage caused by improper transport. If so, please immediately contact the carrier for a claim and report the situation to the company.

2、The control orders and packing list to check whether the goods are complete, product specifications are correct. If the order is complete, the system will be connected, through the static characteristic of the electrical inspection system with single index indicate the factory calibration, usually these indicators should be in accordance with the specifications stipulated in Appendix or the agreed technical agreement.

3、If the product is in good condition, and do not immediately install and use, it is best to carefully put the parts back to the original packaging box, sealed for preservation, for later use.

4、If the inspection is not qualified, please contact us as soon as possible.

Two:Keep in Storage

If not used for a long time, the sensor system should be stored at a temperature of -30℃~70℃, relative humidity of not more than 90% clean room, and indoor air may not contain corrosive gases. Storage period of more than one year, before use should be new calibration.

Three: Specimen Material

Unless otherwise described in order, usually at the factory before the sensor system using 40CrMO materials for calibration specimen material was measured and it only with the series, the characteristic equation and 40CrMO similar to 40CrMO; when the material and components of the measured object is great or not at the same time, please explain in when ordering or providing the measured material sample.

 

Chapter Two   Installation of Eddy Current Displacement Sensor System

                        

 

Section 1  Probe Mounting Clearance

When the probe is installed, should consider the change of linear measurement range of the sensor and the measured clearance volume, when the linear range is measured with the change of the total gap sensor approach, with particular attention to (in order to make the linear range of sensor selection should be selected larger than measured gap of more than 15%). Usually, vibration measurement, the installation gap probe sensor in linear displacement measurement point; when the amount of change according to the displacement direction change or which direction is to determine the installation gap setting. When the displacement is far away from the direction of the probe end, the installation gap should be set in the linear proximal; otherwise, it should be located at the far end of the linear.

 

Adjust the probe mounting gap using the following methods

Connect the probe, extension cable, proximitor, connect the sensor system power output with a multimeter voltage monitoring front-end, and adjust the probe and the measured surface of the gap, the current is equal to the corresponding output voltage or current when the installation gap (the value from the sensor calibration data in single check), the two fastening nuts can be prepared with a tight probe.

 

▲By measuring the proximitor output voltage to determine the installation gap, there may be an illusion: when the probe head is not exposed because of the metal mounting hole, mounting holes around the influence, may make the proximitor output voltage or current output is equal to the corresponding value of installation clearance. Adjust the probe to the correct installation position, the proximitor output should be: first is the saturated output larger (this time has not been put into the installation of Kong Zhong probe), then the smaller output (at the same time, the probe into the mounting hole), will continue to probe into the mounting hole, the proximitor output will become the largest output (the probe head above the mounting hole, but the surface to be measured and the large gap, and then continue to probe into), proximitor output is equal to the corresponding installation clearance value, the probe is the correct installation clearance.

 

             

 

 

 

 

 

General Steps for Probe Mounting

 

1. According to the installation space range, measurement site environment and the measured body size, material properties of the selected sensor, and the visual inspection sensor is intact, whether supporting each part (such as the diameter of the probe and the probe supporting regulations proximitor models are the same, the diameter of cable length plus extension cable length is in accordance with the requirements of pre for the cable length etc.). Usually sets the order of the sensor, in the factory to provide a data check list, check a single note on the calibration of the sensor calibration of each part of the model, number, the user can according to the product and check the mark. And then the sensor probe, extension cable (if any), the front of the specific marker.

2. Each part of the sensor is connected, the power to check the sensor, if the super poor, you need to re calibrate. Special attention should be paid to the calibration of the test specimen material is consistent with the measured material or with similar components.

3. If you do not have a matching installation bracket, you should make the appropriate mounting bracket. External mounting probe bracket is more complex, generally should be ordered.

4. Processing support bracket screw on the base and the bracket mounted inside the probe generally need two screws for fastening, external installation of the probe are generally processing holes with thread in casing.

5. Fastening mounting probe bracket. If it is installed outside the probe, the probe should be fastened, the bracket is screwed into the screw hole of the installation.

6. Adjust probe mounting clearance. For different purposes, there are different requirements for the initial installation clearance of the probe.

 

7.Fastening mounting probe. For the internal installation of the probe, if it is with two nuts tight with angle steel bracket, the clip piece with the fastening screw locking; for external installation of the probe is installed outside the bracket fastening. Fastening screws, nuts should be added spring washers to prevent loosening.

 

 Section 2  Extension cable installation

The extension cable is the middle part of the probe and the connector, and it is also one of the main parts that affect the performance of the sensor. The installation of the extension cable shall ensure that it is not easy to be damaged during use. Recommend the use of pipeline in general, or the extension of the armored cable. Not too long to cut the cable, otherwise it may cause serious error or sensor can not work normally.

In the tray extension cable, because of its material, should be avoided due to disk radius is too small and the cable is broken

In the selection, we should ensure that the length of the extension cable and the length of the probe cable is greater than the length of the probe installation to the installation of the front device, and usually are installed on the front side of the machine is concentrated on the same side.

The extension cable adapter is sealed in insulation

Joint extension cable and probe cable is connected with the signal "land", and has no sealing In order to avoid insulation protection. Usually the heat shrinkable sleeve shrink wrap. In the factory of the company as an attachment to each probe provides a 200mm long section by 8 transparent heat shrinkable sleeve, on-site installation, a section about 100mm long cut, connect the connector, the sleeve at the joint, use hair dryer to heat shrinkage can be. This can also play a role in preventing joint loosening.

*Do not use adhesive tape to insulate the probe connector, because the oil will dissolve the sticky tape and pollute the probe.

 

General procedure for extending cable installation

1. Check Cable Length

Check whether the length of the extension cable is matched with the probe and the front connector, and the length of the extension cable and the length of the cable with the probe should be consistent with the length of cable required by the front connector. Unless otherwise specified, the length of the cable is extended and the length of the cable with the probe is 5m or 9m.

 

2. Connecting Extension Cable

 The adapter cable will be extended to wear to probe the junction box, and a saving of 100 mm long by 8 transparent heat shrinkable sleeve, adapter and cable joint will be extended high frequency cable connection and tighten the heat shrinkable sleeve moved to the junction, the heat shrinkable sleeve length of both sides of the junction, and electricity the blowing and heating heat shrinkable tube, the shrink wrapping connector.

 

Section 3  Pre installation

 

*  The proximitor requirements of the work environment is much more stringent than the probe, usually it will be installed in the danger zone location, the surrounding environment should be dry, non corrosive gas, small vibration, environmental temperature and room temperature difference. In order to ensure the safety and reliability. Installation dimensions are shown in the figure:

             A type shell installation size chart

           Unit: mm

 

 

              B type shell installation size chart

              Unit: mm

Section 4 Sensor system connection

 The system connection includes an electrical connection between the sensor probe, the extension cable (if any), the preamplifier and the monitoring instrument to form a measurement system that can be put into operation. The probe, the extension cable and the front connector are connected by a standard high frequency connector, and a multi-core shielded cable is connected between the front end and the instrument. ML33- A-A preamplifier with 5 core shielded cable connection, usually one of the brown wire connected to the power supply DC24V, blue line signal output (OUT), white line: GAP+. Black line: GAP-, shielded wire grounding. In order to avoid confusion and the wrong line, wiring should be uniform color. Connection system, detection of GAP+ with a multimeter voltage (white) and GAP- (black line) between the voltage value, when the GAP voltage is 10V, said the probe installed in the linear output point sensor.

 ML33-A-A type connector is connected as shown in the following figure:

  •Sensor wiring diagram

                                         

        

  Output Mode Selection

   A:  Current 4~20mA output        22-30V DC power supply

  V2-1: Voltage 0~10V output      ±15V DC--±18V DC power supply

  V2-2: Voltage 0~10V output       + 12V DC power supply

  V2-3:Voltage 0~10V output      + 24V DC power supply

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