Application of DC Sensors in Electrolysis Industry

The main materials of the DC sensor core and gallium arsenide Hall element are imported from Japan, but after special processing and circuit design, the components in the design are made of domestic military products. According to the voltage signal converted by the current and magnetic field collected by the Hall element in the magnetic path gap, the full current law and new technology are applied; the new process method is successfully developed.

The product was praised by users for its use of Baling's ion-exchange membrane caustic soda equipment.

DC power metering plays a decisive role in the electrolysis industry management. It is one of the main technical assessment indicators for enterprises to increase efficiency and tap potential. It is also one of the regulatory signal sources that guarantee the smooth operation of the rectifier power supply. Therefore, the DC sensor is used in the rectification power system. Accurate measurement, stability and reliability are especially important.

As we all know, the current DC current sensor popular in the domestic market separates the ring from the closed-loop two forms (also known as the direct measurement type and the zero detection type), and the two types of sensors have their theoretical basis in terms of measurement accuracy. The voltage signal converted by the Hall element in the air gap of the magnetic circuit is directly proportional to the current and the magnetic field. It is designed and manufactured under the theoretical framework of the full current law.

SDA series DC high-current sensors can meet the needs of different industries and different manufacturers in the electrolytic industry, and can produce a wide range of closed-loop and open-loop type products. 5KA~420KA DC high current can be measured online, with high accuracy, reliability and stability, fast response, easy installation and maintenance, and other products have been included in Hubei Province "Torch Plan", "Science and Technology Research Plan "National new product trial production and appraisal plan"; and Hubei Province, "second prize for scientific and technological progress", the State Science and Technology Commission "Golden Bridge Award" and "national new product certificate."

Our company's products are produced under the ISO9001-2000 quality management system strictly in accordance with international standards, relying on a strong, experienced R&D team to back up, using new technologies, new materials, new processes and other means to ensure Our company's products have always maintained at the forefront of the times in terms of performance and various technical indicators.

Our DC high-current sensor is developed on the basis of the full current law ∫LHdL=I. The core of the full-current law is: the closed-line integration of the magnetic field strength only intersects the current of the closed integration path (measured current I). Relevant, it has nothing to do with the position of the current and the non-interlinked current (the generated stray magnetic field), when the current through the sensor window is zero, no matter whether there is current in the adjacent guide row (relative to external magnetism), the sensor The output must be zero. We know that the measured current I generates magnetic flux Φ in the core, and use the uniform unbranched magnetic circuit with an air gap to convert the measured current I into the magnetic induction intensity in the air gap, according to the loop law of magnetic field strength H1d+H2d+... ... H2Nd + ∫ LHid1 = I and the output voltage of the Hall element UH = KHIHB and the sensitivity, control current and magnetic field strength, the sensor is designed into a certain core area and a certain air gap length, in the magnetic circuit in accordance with the central symmetry and axisymmetric The principle is to add the induced potential induced by the magnetic field strength in the Hall element in each air gap channel and to amplify N times, ie, to obtain an output voltage proportional to the actual current. Assume that the Hall detection channels and the corresponding air gap channels are 2N (designed as even numbers and arranged in the magnetic circuit according to the principle of center and axis symmetry), the width of each air gap is d, and the total length of the core is set to L has:

H1d+H2d+...+H2Nd+∫LHid1=Io...(1)

Among them, Hi (i=1, 2,..., 2N) is the magnetic field strength in the air gap channel, H1 is the intensity at the core of the iron core, and Io is the current in the field bus.

For the air gap, Hi = Bi/μ0, and from the median theorem, there is ∫ LH1d1 = HLL = BLL / μrμ0

Thus: B1d+B2d+...+B2Nd+BLL/μr=μoIo

In the above relation, according to the boundary condition of the magnetic medium, it can be seen that BL and Bi are approximately equal, and the value of L/d in the device design is usually in the range of about 10 to 30, and the value of μr is usually more than four orders of magnitude. The value of BL/μr is small in the sum terms, so that BLL/μrμ0=βμ0I0 (and β′1) can be obtained:

B1+B2+...+B2N=(1-β)μ0I0/d...(2)

On the other hand, it can also be concluded:

BL≈μ0I0/2Nd...(3)

β≈L/2Ndμr......(4)

In sensor debugging, let SH1I1 Sinψ1=SH2I2 Sinψ2=...=SH2NI2N Sinψ2N=K be substituted by VHi=SHiIiBiSinψ1 (2).

VH1+VH2+...+VH2N=K(1-β)μ0I0/d

In the electronic circuit, we add each Hall induced potential and multiply Q times as the output signal Vo of the device, namely:

Vo=Qk(1-β)μ0I0/d...(5)

This equation reflects the relationship between the output voltage Vo of the detection device and the magnitude of the primary detection current Io.

From the above theoretical analysis, the factors affecting the accuracy of the sensor measurement largely depend on the choice of core and Hall devices. Therefore, we spent a lot of energy to conduct a large number of tests on a variety of ferromagnetic materials, and finally selected a new type of magnetically conductive material produced by Nippon-Ishichi Corporation to ensure the performance of the magnetic material as much as possible before and after the magnetic material was formed. It was treated with a special process structure, so that the 5000-8000 Gaussian permeability of our original magnetic material was suddenly increased to the current 17,000-20000 Gaussian theoretical requirement of high magnetic permeability and low coercive force, thus making our The sensor is effectively guaranteed in linearity.

In the same way as in the Hall part, we have also done a lot of tests and screenings in strict accordance with the requirements of theoretical calculation accuracy. Eventually we identified the TO90A gallium arsenide Hall element produced by Nisera of Japan. Its greatest advantage is Its temperature stability during constant current operation is typically -300 to -400PPm/°C, with good output linearity. The maximum error is only 0.8%. The output voltage of 1mA1kGS can reach about 65-170mV and has good frequency characteristics. The theoretical band width is above 1 M Hz, as long as its excitation current does not exceed 3.5 mA, and its service life can reach more than 200,000 hours.

In order to ensure that the sensors produced by our company are used in the field with high reliability, high stability and high precision, and on the basis of new materials, the original industrial grade components are replaced with the current military grade components and circuits. The board was changed from the original copper-clad board to the current double-sided gold-plated board. All the original electrical connectors were changed to the current fasteners to ensure the high reliability of the product. In the manufacturing process, we used a two-level automatic temperature. The compensation technology has carried out a large amount of research and experimental work on the compensation process of a single Hall element. A Hall-type compensation process is adopted for the physical characteristics and material characteristics of the Hall element to make the Hall element compensation accuracy and stability. Compared with the previous thermistor compensation process has been greatly improved, in order to prevent the influence of the external temperature on the sensor, the electronic circuit part is concentrated in a self-controlled thermostatic box, avoiding a local part caused by the temperature coefficient caused by the system offset The amount of change, thus ensuring the high stability of the product; in the circuit structure we will put the original differential Circuit into the present three differential amplifier circuits, eliminating the input resistance of the Hall element is greater than the output resistance of the operational amplifier to generate an error. In the sensor's post-amplifier circuit uses multi-stage isolation amplifier output, the output signal does not interfere with each other, so that the connection of high-current DC meter control system is very convenient. In multiple parallel rectifiers, when one of them is out of power, the reverse short-circuit current generated by the short-circuit on the DC network side is very large, and the limit value of the sensor counter-current protection contact is set to achieve the reverse protection of the rectifier unit.

Through a large number of theoretical researches and practical explorations, the large-current DC metering and control system produced by our company has been continuously improved and optimized, and it has been widely praised in the market. Especially in the chemical industry, Baling Petrochemical Company's 50,000 tons of ion-exchange membrane caustic soda DC power system applications.

Our company's products have been favored by customers with its high precision, high reliability and stability, and have eliminated Halmar's products and received praise from the chlor-alkali industry. This has greatly encouraged the ambition of the national industry. The outstanding advantages of our products are shown in the following aspects:

First, the structure is simple: Our company's SDA series DC large current sensor is an open type two-part docking method, installation, use, maintenance is very convenient, with small size, light weight, power consumption and other advantages.

Second, high precision: Our company's DC large current sensor is based on the full current law, based on the use of secondary temperature automatic compensation technology and optimization of circuit design technology, the magnetic circuit in accordance with the principle of center and axis symmetry, selected the latest The type of material and process technology ensure the theoretical calculation accuracy of the product in practical applications. Three-stage differential amplifier circuit is adopted to eliminate the error caused by the output resistance of the Hall element being greater than the input resistance of the operational amplifier, so that the sampled value is reflected without distortion and reaches the design requirement.

Third, the stability is good: Our company's DC large current sensor is based on the principle of symmetry, the air gap in the closed magnetic circuit is evenly distributed evenly, the technical parameters of the Hall parts are strictly matched, using a unique The remanent magnet circuit improves the product's resistance to external magnetic interference, and uses secondary temperature auto-compensation technology to prevent the product from being affected by the external ambient temperature. The use of fully enclosed anti-corrosion and dust-proof measures but not sealing the Hall part in the air gap is intended to avoid that if a Hall part is damaged and cannot be replaced, the symmetry is completely lost even if a false value is not adjusted on the circuit. As a result, the influence of eccentricity errors cannot be guaranteed.

Fourth, high reliability: Our company's products due to the strict selection of military-grade components, so that the reliability of the product has been greatly improved, for all electrical connections using solid pieces of contact, sensor power supply using independent power supply, sensor The various output signals are isolated and not interfered with each other. Double shielded cables are used for cables connected to various instruments and meters. As long as one end is reliably grounded, the interference introduced by the line can be effectively suppressed.

V. High qualifications: The company has the only domestic 420KA high-current standard signal debugging source approved by national authoritative institutions, which ensures that our company has the only standard debugging capability in the full range of high DC current, making it full. Linearity and accuracy within the range are effectively guaranteed.