Characteristics of differential expansion sensor

JY210 Series Eddy Current Sensor User Manual

One Working principle and characteristics of differential expansion sensor

The basic working system of a differential expansion sensor 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, and 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), causing a change in the Q value of the coil. When the distance is small, the eddy current effect is strong and the Q value of the coil is small; When the distance is large, the eddy current effect is weak and the Q value of the coil is high. In practical applications, the change in coil Q value is detected and amplified by a preamplifier to convert it into a change in voltage. Realize the conversion of mechanical displacement (gap) values into voltage values.

In summary, the material of the measured object in the working system of the eddy current sensor is closely related to the measurement results.

The influence of the tested material on the sensor characteristics: displacement (mm)

Material impact data curve

When placing an order, the user must specify the material, shape, size, etc. of the tested object. If the user does not specify in the contract, 45 # steel will be used as the tested material during factory calibration, and the diameter of the tested surface will be calibrated to be greater than or equal to 3 times the diameter of the probe.

II Characteristics of differential expansion sensor

▲ Reliability:

=The probe head body is made of PPS engineering plastic and molded through a mold. Ensure that the probe has high strength, high temperature resistance (220 ℃), and corrosion resistance; Not easily damaged and will not corrode even when exposed to certain chemicals; Ensuring the reliability of the probe;

=The coaxial cable and extended coaxial cable used for probe signal output are imported wide temperature range cables (-55 ℃~200 ℃); High cable strength and good consistency of electrical characteristics (beneficial for reducing interchangeability errors);

=The cable joint uses imported standard plug sockets, 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 the ability to prevent lightning strikes and suppress power grid peak interference, making it safer;

▲ Temperature stability and accuracy:

=By relying on advanced compensation circuits, the maximum deviation of the probe coil and cable temperature changes within the temperature range of (-22 ℃~120 ℃) is less than ± 5% (including linear and sensitivity deviations);

=Probe sensitivity error ± 3%;

=Probe linear error ± 1%;

=Frequency response DC~5 kHz

=Resolution of 1um

III Technical parameters of differential expansion sensor

=Basic requirements for the working environment of JY210 series differential expansion sensor:

Probe -30 ℃~150 ℃, extension cable -30 ℃~200 ℃, preamplifier -30 ℃~80 ℃; In an environment with a relative humidity of 95%, long-term operation will not cause damage.

=Power supply: -24VDC ± 10%

=Dimensions: 80mm × 60mm × 30mm

=Installation can be done using guide rails or screws.

=Technical indicators:

At room temperature of 25 ℃, the tested material is 45 # steel, with a power supply of -24V ± 10% and a load of 10K Ω. The following conditions are met:

4、 On site installation and debugging

（1） General steps for probe installation

1. Select the sensor based on the measurement range of the measuring part, the environment and size of the installation space, and the characteristics of the measured material, and check whether the appearance of each part of the sensor is intact and whether each part is compatible. Sensors that are usually ordered as a complete set are provided with an inspection form at the factory, which indicates the model and number of each part of the sensor that is calibrated and matched. This can be used to verify the markings on the product. Then, specific markings (such as "1 # tile horizontal vibration", "axis displacement", etc.) should be made on the probe, extension cable (if any), and preamplifier of the sensor to explain their function and distinguish the connection relationship between different parts of multiple sets of sensors. The two ends of the cable should be marked to distinguish between multiple cable heads, and these markings should be oil and waterproof.

2. Connect the various parts of the sensor, power on to check the linearity, sensitivity, etc. of the sensor. If it exceeds the tolerance, it needs to be recalibrated. During inspection, special attention should be paid to whether the material of the calibration specimen is consistent with or has similar composition to the material of the tested object.

3. Screw the probe into the installation screw hole.

4. Adjust the installation gap of the probe. The initial installation clearance of probes for different purposes has different requirements:

Axial displacement and differential expansion: Install according to the zero point of the instrument;

Vibration, phase detection, eccentricity: installed at the linear midpoint of the sensor.

5. Tighten and install the probe.

6. Fixed probe cable: Install the probe cable internally, first fix it with a cable fixing bracket inside the machine, then thread it through the cable sealing device, and then tighten the cable sealing component (when multiple probes share the same cable sealing device, tighten it after all probe cables are threaded through); To install the probe cable externally, simply tighten the cable sealing component on the bracket.

（2） Installation of extension cables

As an intermediate component connecting the probe and the preamplifier, the installation of the extension cable should ensure that it is not easily damaged during use. Usually, pipeline laying is used, otherwise armored extension cables should be used. In addition, the excessively long cable should be coiled into a circular ring with a diameter of not less than 50mm, tied tightly with ropes, and fixed with pressure plates. The excessively long cable should not be cut off arbitrarily.

When selecting, it should be ensured that the sum of the length of the extension cable and the length of the probe cable is greater than the distance from the installation location of the probe to the installation location of the preamplifier, and usually the preamplifier is concentrated on the same side of the installation machine.

Sealing and insulation of extension cable adapters

The outer skin of the extension cable is insulated and sealed with poly plastic, and the internal structure of the probe is also insulated. However, the joint between the extension cable and the probe cable is connected to the signal "ground" and does not have sealing properties. Due to the fact that the connection between the extension cable adapter and the high-frequency connector of the probe cable is usually suspended in the junction box, insulation protection should be provided at the connection to avoid contact with the casing and enhance its sealing. A better method is to use heat shrink tubing to shrink wrap. When the product leaves the factory, our company provides a section of transparent heat shrink tubing with a diameter of 100mm for each probe as an accessory. During on-site installation, a section of about 50mm is cut off, and after connecting the joint, the tubing is placed over the joint and heated and shrunk with a hair dryer. This can also prevent the joint from loosening. If it is necessary to disconnect the joint, simply use a blade to carefully cut open the heat shrink sleeve, and then reconnect the joint by cutting another intact section of non shrink sleeve and tightening it.

Laying extension cable conduits: In order to protect the cables from damage, conduit laying is usually used to lay extension cables.

General steps for installing extension cables

① Check the length of the extension cable

Check if the length of the extension cable matches the requirements of the probe and preamplifier. The length of the extension cable plus the cable length carried by the probe should be consistent with the cable length required by the preamplifier, unless there are special specifications. The length of the extension cable plus the cable length carried by the probe should be 5m or 9m. If it is a complete set order, the model and number of the probe, extension cable, and preamplifier used for system calibration are usually indicated on the factory calibration form, and the system is composed of the product number on the factory calibration form.

② Marking extension cables

Special markings (such as 1 # watt horizontal vibration, etc.) should be made at both ends of the extension cable to illustrate its function and distinguish the connection relationship between multiple sets of sensors. The cable ends should be marked for identification among multiple cable heads, and these markings should be oil and waterproof.

③ Laying extension cables

If pipeline laying is used, the pipeline should be installed in advance, and the inside of the pipeline should be checked for cleanliness, no sharp protrusions or rough surfaces to prevent contamination and scratching of the cable. When passing the cable through the pipeline, the first step is to use a rubber sleeve (each joint is covered with one when the product leaves the factory) to cover the joint that needs to be inserted into one end of the pipeline (whether it is an adapter or a high-frequency joint, depending on which end of the pipeline the extension cable is inserted into; from near the preamplifier installation box, the adapter should be inserted into the pipeline; from near the probe junction box, the high-frequency joint should be inserted into the pipeline) to protect the joint from contamination.

If pipeline laying is not required, armored extension cables need to be selected. During installation, cable clamps or similar devices can be used to secure the extension cable in a safer location to reduce the risk of cable damage.

④ Connecting extension cables

Insert the adapter of the extension cable into the probe junction box and cover it with a 50mm long transparent heat shrink sleeve. Connect the extension cable adapter to the high-frequency connector of the probe cable and tighten it. Move the thermoplastic sleeve to the connection point so that the length of the heat shrink sleeves on both sides of the connection point is the same. Heat the thermoplastic tube with a 750W hair dryer to shrink and tighten the connector.

（3） Installation of the preamplifier

As a signal processing component of a sensor system, the preamplifier has much stricter requirements for the working environment than the probe. It is usually installed far away from hazardous areas, and its surrounding environment should be free of corrosive gases, dry with minimal vibration, and the ambient temperature should not differ much from room temperature. In order to ensure the safe and reliable operation of the preamplifier, it is necessary to use a dedicated preamplifier installation box. Our company can provide you with explosion-proof installation boxes and ordinary metal installation boxes with explosion-proof certificates, and has processed the installation guide rails of the preamplifier according to the installation dimensions.

Before use, the installation box of the preamplifier should be purified with compressed air to ensure that there is no residual liquid or metal shavings inside the box, otherwise the metal shavings may cause a short circuit in the wiring terminals of the preamplifier. An excessively long probe or extension cable should be fixed in a location that does not come into contact with the preamplifier.

In order to prevent interference caused by different ground potentials, a single point grounding must be used. In order to shield external interference, the preamplifier housing is directly connected to the system electrical system, so the preamplifier mounting box, mounting screws, and preamplifier housing should be insulated. The insulation base plate has been added in the design and manufacturing of the preamplifier, so there is no need to consider the insulation issue of the preamplifier.

The API670 standard recommends installing the preamplifier mounting box on the same side of the machine for easy cable laying and maintenance inspections.

（4） System connection

The system connection includes electrical connections between the sensor probe, extension cable (if any), preamplifier, and monitoring instrument to form a measurement system that can be put into operation. The probe, extension cable, and preamplifier are connected through their standard high-frequency connectors; Connect the preamplifier and monitoring instrument with a three core shielded cable. Usually, the red wire is connected to the power supply (Ut terminal), the black wire is connected to the signal ground (COM terminal), and the yellow wire is connected to the signal output (OUT terminal). The allocation of various colored wires is based on the 16AG multi-core shielded cable specifications. If other types of cables are used, it will be different, but the wiring should be consistent to avoid misconnection due to confusion. The shielding layer of the shielded cable needs to be grounded at a single point at one end of the monitoring instrument.

The maximum distance between the preamplifier and the monitoring instrument should not exceed 300m, otherwise the signal attenuation will be too large.

Five Calibration and Maintenance

This chapter mainly explains when to calibrate the sensor system and how to repair the sensor system when a malfunction occurs.

（1） Calibration

Under what circumstances should sensors be recalibrated

=The sensor has not been used for a long time for more than one year;

=The sensor has been used continuously for two years;

=The tested material does not match the factory calibration material;

=After troubleshooting.

Quasi devices and equipment

=Displacement calibrator

=Micrometer

=Digital multimeter

=DC stabilized power supply

Our company can provide the above tools and equipment.

calibration steps

=Select the same specimen as the tested material and install it properly.

=Install the probe and micrometer (the range should be 20% greater than the sensor range).

=Adjust the supply voltage of the DC stabilized power supply to the voltage range required by the sensor system.

=Connect the stabilized power supply, digital multimeter, probe, and cable to the preamplifier separately

=Rotate the micrometer adjustment knob to make the probe closely adhere to the plane of the specimen, and then adjust the distance between the probe head and the specimen to the linear starting distance of the sensor.

=Turn on the power, rotate the micrometer adjustment knob, and record the sensor output voltage or current value at intervals of one tenth of the range.

=Calculate the sensitivity and linear error of the sensor.

=If the nonlinearity, sensitivity and other indicators exceed the tolerance, please contact our company and have professional technicians adjust them.

（2） Malfunctions and Maintenance

When abnormal phenomena occur during calibration or operation of the sensor system, first conduct a preliminary inspection on your own. If the problem is serious, please contact our company.

Preliminary inspection steps

=System check

1) Is the wiring terminal connected incorrectly;

2) Is there a short circuit in the wiring;

3) Is the power supply voltage correct;

4) Check if the measuring instrument is short circuited or open circuited.

=Probe maintenance

1) Check if the high-frequency plug and probe head of the probe are clean. If there is any dirt, please clean them with alcohol.

2) Is the extension cable (if any) short circuited or open circuited? If there is a fault, the extension cable should be replaced.

3) Check if the probe is short circuited or open circuited: First, disconnect the extension cable (if any), and then use a digital multimeter to measure the resistance value between the high-frequency plug housing of the probe. The normal value should be between 2.0 and 15.0 Ω. If the resistance value is very small (less than 1.0 Ω), it indicates that the probe is short circuited; If the measured resistance value is very large (greater than 100 Ω), it indicates that the probe has an open circuit or poor contact. When there are the above two situations, the probe needs to be replaced.

=Front end device maintenance

1) First, check if the probe and extension cable are compatible with the preamplifier. If there is an extension cable, it must be connected.

2) Connect the probe that has been determined to be intact to the preamplifier. When the probe head is close to the metal conductor, the output value of the preamplifier should be minimized; When the probe head is far away from the metal conductor, the output value of the preamplifier should be at its maximum. Otherwise, it can be determined that the preamplifier is damaged or the sensor system has poor contact. In this case, the system should be repaired or the preamplifier should be replaced.