Current measurement technology in the automatic de

  • Detail

Current measurement technology in packaging automatic detection system

[i according to the current situation that current measurement technology is rarely used in the automatic detection system, the concept of current measurement using the magnetic field generated by current is proposed, a non-invasive current sensor based on the principle of electron beam deflection in the magnetic field generated by the measured current is described in detail, and the problems faced by this current measurement technology are discussed, and the corresponding solutions are proposed. Finally, the relevant current data and its The analysis method of related signals and the significance of current measurement. [/i

key words: current measurement; electron beam deflection; magnetic field; current sensor

1 Introduction

voltage measurement is usually used in automatic detection system to determine circuit faults. In practical work, current is rarely used for detection. Mainly because current detection meets two difficult problems: one is the lack of effective non-invasive current sensor; the other is that it is difficult to intervene in current branch for measurement. The traditional current measurement is to measure the voltage drop at both ends of the shunt resistance in the access branch of this product through the voltage sensor. Due to the need to access the shunt resistance, the test process is very inconvenient and difficult to realize automation. Some instruments have applied some new technologies, such as adding a built-in current sensor to VXI/PXI instruments, which can be controlled by software for steady-state measurement. However, these sensors cannot measure high-frequency sampled signals, so they cannot capture high-speed transient signals. In order to obtain current data, a non-invasive sensor without intervention circuit is required. In addition, a software system for analyzing current data and other related measurement signals is also required

2 current sensor

current sensors include Hall effect type, magnetoresistance type, resistance type, etc. The principle of the current sensor introduced in this paper is to measure the deflection of pulsed electron beam in the magnetic field generated by current. Because the electron mass is very small, the force required to deflect the moving electron beam with the 1064 nm laser rangefinder is relatively small, which makes it theoretically feasible to measure the small magnetic field through the deflection of the electron beam

the application of magnetic field to deflect electron beam is very common in technology, and it is widely used in cathode ray tube displays of TVs and computers. The concept of electron beam deflection is not an innovation in itself, but it has not been widely used in the field of magnetic field measurement, especially in the magnetic field generated by current. In addition, high voltage and high current are usually required to generate electron beam and control electron beam deflection. High voltage and large current generate considerable magnetic field and static electric field. Therefore, the first technical challenge of using electron beam to measure magnetic field is how to use small voltage and current to generate electron beam

the sensor system measures the deflection of the pulsed electron beam generated by a low-voltage photoelectric device

the current sensor is composed of an electron beam generating element, an electron beam collecting element and an electron beam deflection measuring element, as shown in Figure 1. The electron beam generating element includes a light-emitting diode, which is usually 2 V, 50 Ma and 120 light energy. The optical lens is used to focus the light produced by the photodiode on the cathode-ray tube and enhance the light intensity per unit area. One side of the cathode ray tube is illuminated by the light generated by the light-emitting diode, and the other side emits electron beams. The electrode ring prevents the electron beam from escaping around and limits it to a tight beam, which is a mandatory requirement to maintain measurement accuracy. The electron beam collecting element includes a vacuum cavity, and a small amount of negative potential is maintained on the inner wall of the vacuum cavity to prevent the electron beam from being attracted by the cavity wall. An uninsulated linear charge coupled device cavity is used to measure the intensity and induction point of the end of the electron beam impact sensor for induction. Charge coupled devices CCDs are used to measure photon intensity, while CCDs are designated as non insulated and can be used to collect electrons. The energy of collecting a photon is about 2.14 V, so the electron beam pulse with potential difference higher than 2.14 V has enough energy to excite a typical CCDs. The potential of CCDs itself is kept at about zero potential, and some changes in the potential have both advantages and disadvantages. The best potential that does not cause repulsion or attraction to the electron beam can be obtained through experiments. The top of CCDs initially carries a small amount of positive potential to attract and accelerate the electron beam

current measurement: the force direction of positive particles in the magnetic field can be judged by the "right hand rule", and the corresponding formula is:

fb = QV × B

as the current increases or is closer to the measured current, the magnetic field strength will increase, and the corresponding electron beam deflection will increase. As the deflection of the electron beam increases, the electrons collected by the CCDs will fall away from the apex of the sensor. When other parameters are determined, the current value can be determined by the position where the sensor absorbs the electron beam. The dynamic value (transient signal) of current can be obtained by continuous measurement of the same test point. By analyzing the transient signal of current, many valuable new information can be obtained, such as impedance in complex domain

3 measurement technology

several technical problems that need to be solved in current measurement with non-invasive current sensor:

(1) the influence of the distance between the sensor and the measured current carrier on the measurement results

the strength of the magnetic field is inversely proportional to the distance between the current generating the magnetic field and the sensor. This distance is usually unknown and unmeasurable. The relative position between the magnetic induction sensor and the measured current carrier (conductor, printed circuit board wiring, output end) has a great impact on the measured value. In order to reduce this impact, the measurement process, including measurement steps and software tools, has been tried. For example, the user must "scan" the current carrier through which the current flows and capture its maximum value with software. Ideally, the distance between the sensor and the measured object should be 0. In many practical cases, the tested object is wrapped in an insulator. The result of the attempt is that the measurement process cannot be eliminated, but can only reduce this effect. However, there is a parameter that is not affected by distance, which is the "shape" of the measured transient signal. The "shape" of the transient signal contains some information, such as damping rate (the rate of amplitude attenuation), natural frequency (crystal frequency). Lai Y C et al. Reacted with neopentyl 2 alcohol (NPG), polypropyl 2 alcohol and IPLI to obtain the participating catheter of Shangjin medical, which is well-known in the Japanese market. The product is a prepolymer named inp4h, which is then UV cured with hydrophilic monomers to obtain a polyurethane film, which swells to a balanced weight in a buffer solution to obtain a PU hydrogel. Another idea is based on the characteristics of this distance, which is unpredictable but controllable, A current information image template of a fault free circuit can be established at a certain position, and the difference between the circuit to be tested and the known template can be detected

Copyright © 2011 JIN SHI