Hello everyone, today I'd like to share some basic introductions about the metal detector. Are you familiar with it in your mind and where you feel you've seen it? For example, when we go through the security check, we scan the metal detector. This is the most common. Let me introduce it to you in detail.

 

Metal detector is a kind of metal detection device, which is composed of metal detector and automatic removal device, in which the detector is the core part. The system can use the alarm signal to drive the automatic elimination device, so as to exclude metal impurities from the production line.

 

Three groups of coils are distributed inside the detector, namely, the central transmitting coil and two equivalent receiving coils. The oscillator connected to the transmitting coil in the middle generates a high-frequency variable magnetic field. In the idle state, the induced voltages of the receiving coils on both sides offset each other before the magnetic field is disturbed to reach a balanced state.

 

Once the metal impurities enter the magnetic field area and the magnetic field is disturbed, this balance will be broken, and the induced voltage of the two receiving coils cannot be offset. The non offset induced voltage is amplified and processed by the control system and generates an alarm signal (metal impurities are detected). The system can use the alarm signal to drive the automatic elimination device, so as to exclude metal impurities from the production line.

 

The components used in metal detectors have developed from electronic tubes, transistors and even integrated circuits. Their application scope has been expanded to almost all fields, which plays an important role in industrial production and personal safety

 

characteristic

 

The accuracy and reliability of the metal detector depend on the stability of the frequency of the electromagnetic transmitter. Generally, the working frequency from 80 to 800 kHz is used. The lower the working frequency, the better the performance of iron; The higher the working frequency, the better the detection performance of high carbon steel. The sensitivity of the detector decreases with the increase of the detection range, and the size of the induced signal depends on the size of metal particles and conductivity.

 

Due to the current pulsation and current filtering, the metal detector has a certain limit on the conveying speed of the detected articles. If the conveying speed exceeds a reasonable range, the sensitivity of the detector will decrease.

 

In order to ensure that the sensitivity does not decrease, appropriate metal detectors must be selected to adapt to the corresponding tested products. Generally speaking, the detection range shall be controlled at the minimum value as far as possible. For products with good high-frequency induction, the size of detector channel shall match the product size. The adjustment of detection sensitivity shall be determined by referring to the center of the detection coil, and the induction of the center position is the lowest. The detection value of the product will change with the change of production conditions, such as temperature, product size, humidity, etc., which can be adjusted and compensated through the control function

 

Spheroids have repeatability and the smallest surface area, which is also the most difficult to detect for metal detectors. Therefore, the sphere can be used as a reference sample for detection sensitivity. For non spherical metals, the detection sensitivity largely depends on the position of the metal. Different positions have different cross-sectional areas, and the detection effect is different. For example, when passing longitudinally, iron is more sensitive; High carbon steel and non iron are less sensitive. When passing laterally, iron is less sensitive, while high carbon steel and non-iron are more sensitive.

 

In the food industry, the system usually uses a high operating frequency. For foods such as cheese, due to its inherent good high-frequency sensing performance, it will increase the response of high-frequency signals in proportion. Wet fat or salt substances, such as bread, cheese and sausage, have the same conductivity as metals. In this case, in order to prevent the system from giving wrong signals, the compensation signal must be adjusted to reduce the induction sensitivity.

 

The metal detector is divided according to its functions:

 

1) All metal detector: it can detect all metals such as iron, stainless steel, copper and aluminum. The detection accuracy and sensitivity are relatively high, stable and reliable.

 

2) Iron metal detector: it can only detect iron metal, commonly known as needle detector. The detection accuracy and sensitivity are low and easy to interfere.

 

3) Aluminum foil metal detector: it can only detect ferrous metals, but its detection accuracy and sensitivity are still high when detecting products packed with aluminum foil.

 

Influence of product effect on the performance of metal detector:

 

The tested non-metallic materials generally have a certain product effect, and the size of the product effect directly affects the working performance of the metal detector. Digital metal detector uses the ability of digital signal processing to compensate the product effect, which can reduce the influence of product effect on the metal detector in the working process. It can improve the detection performance of the metal detector.

 

General manufacturers often solve this problem from three aspects.

 

1. Using the understanding of the characteristics of product effect and adopting the way of intelligent recognition to distinguish the difference between metal and product effect, so as to improve the working performance of metal detector; Generally, it can achieve good detection performance, but the detection of aluminum foil packaging products needs special customization.

 

2. Using different product effects to improve the performance of the detector according to the different working frequency of the detector, but the problem is that this method will reduce the sensitivity to non ferromagnetic metals, which often improves the performance of ferromagnetic metals but reduces the sensitivity of stainless steel.

 

3. Metal detector using two or more frequencies and characteristic analysis; This method is a compromise technology, which can achieve a certain effect. Generally, the working condition will improve the detection sensitivity of some ferromagnetic metals, but the performance improvement of stainless steel is limited.

 

The size of the product effect is not only related to the conductivity or magnetic characteristics of the product, but also related to the volume of the tested product. When the product property is certain, the larger the product package, the stronger the product effect, and the stronger the product effect, which will affect the sensitivity of the detection. In the food industry, due to the particularity of its equipment, the performance of the detector for stainless steel detection is often demanding. Therefore, the general intelligent identification method of the detector has a better effect in practical application.

 

Handheld metal detectors are designed to detect metal objects carried by people or objects. It can detect weapons, explosives or small metal objects carried by people or in packages, luggage, letters, fabrics, etc. The special appearance of its sensitive surface makes it easy to operate. It is better than ring sensor hand detection. Ultra high sensitivity, special application. Such as prison, chip factory, archaeological research hospital, etc

 

Application neighborhood

 

Underground metal detector is made with advanced technology. It has the characteristics of wide detection, accurate positioning, strong resolution and simple operation. Metal detector is mainly used to detect and identify buried metal objects. In addition to its military application, it is also widely used in safety inspection, archaeology, prospecting and looking for waste metals. Also known as "iron detector", it is a good helper for waste recycling.

 

The underground metal detector adopts sound alarm and instrument display. The detection depth has a great relationship with the area, shape and weight of the detected metal. Generally speaking, the larger the area is, the more the quantity is, the greater the corresponding detection depth is; On the contrary, the smaller the area, the less the quantity, and the smaller the corresponding depth. The maximum detection depth listed in the following table is the measured result of embedding a 60cm * 60cm * 0.5cm aluminum plate into the dry soil according to the enterprise standard of the product.

 

major function

 

1. Ground balance line is set, which can eliminate the influence of "mineralization reaction" and greatly improve the depth and accuracy of effective detection;

 

2. It has the function of distinguishing ferrous metals from non-ferrous metals;

 

3. Adopt intelligent operating system;

 

4. It is packaged with high-strength ABC material, with light weight and long service life;

 

5. Metal sound can be recognized through headphones.

 

6. If the metal is buried underground and detected through the thick soil layer, it must be affected by the geological structure. There are various minerals in the stratum. They will also make the metal detection produce signals. The signals enough to write minerals will mask the metal signals and cause false images. People who have used the old metal detector have this experience. As the probe approaches the mound, stone and brick, an alarm will sound. This phenomenon is called "mineralization reaction". For this reason, the old metal detector can only detect the metal in shallow soil and can't do anything about the metal targets buried deep underground.

 

7. Detection range: about 1.5m

 

Well, that's all for our introduction. If you have any questions, please leave a message. If you want to know more, please pay attention to us. See you next time.