Advantages of high precision fluxgate current sensor in high current precision measurement

The so-called large current, the scope is fuzzy. Generally speaking, it is not very common, difficult to find a measuring instrument, also difficult to produce a large current (range). One said, >=30A even large current, at this time the vast majority of the multimeter can not be directly measured, and the common power supply is rare to output 30A. On the other hand, you have to >=100A to be really high current. There is no standard, opinions vary, so on a case-by-case basis.

High current exists widely in industry and electric power, so how to measure and measure high current is a problem that must be discussed.

Large current due to the relationship between the current, to be relatively thick lead and related joints, power supply, also involves large heating power, so whether it is volume, weight, price are very spectacular; Simple and precise large current measurement, often suddenly think of using shunt, such as Fluke A40B, but the volume, price and additional equipment is often too large to accept.

The generation of precise large current requires not only precise current measuring device, but also high power and integrated power supply technology. Although it is easy to measure large current, many clamp watches are based on linear Hall principle, which has no high precision. Not even the Roche coil.

One, diverter

The shunt is the most common way to measure current, but it becomes complicated when large currents and high accuracy are involved. First of all, 50mV-75mV is too small, and high precision requires a high degree of voltage output, so as to reduce the influence of thermoelectric motive force and to provide convenience for the follow-up measurement circuit, but the high voltage output in the case of large current is bound to produce a lot of power and heat, so that not only the measured circuit may have an impact, more mainly caused by heat thermoelectric motive force and very large temperature drifts, And of course there's stress and accelerated aging. For example, if 100A current output 1V voltage, the power is 100W, the heating power must be sent out in time as far as possible, in order to ensure that the drift caused by the temperature coefficient is reduced to a minimum. The diverter has another problem is that the deviation and temperature drift are not small, not suitable for use as a high precision.

2. Transformer

Although there are standard current transformers with higher accuracy, up to level 0.01, they can only measure AC.

Three, magnetic balance current sensor

The structure is somewhat similar to that of the transformer, with annular core, primary side threading 1 turn and secondary side multi-turns, but the core has openings, and zero hall devices are placed in the gaps. The secondary side passes with the same ampere-turn size and opposite direction of the current, and the imbalance with the primary side will be detected, and the secondary side coil will be balanced after amplification. At the same time, this secondary side current flows through the measuring resistance Rm to achieve the purpose of current measurement. At this time, Hall devices mainly detect whether there is a magnetic field, so the linear, temperature drift and other requirements are very low, so the accuracy is high, depending on the balance degree of the coil, magnetic permeability, magnetic leakage and so on.

Four, fluxgate current sensor

Compared with the above magnetic balance mode, the fluxgate current sensor is also closed-loop zero-flux detection, but the magnetic circuit is closed. The linear Hall zero-flux detector is removed and replaced by an extra detection coil. The nonlinear characteristics of high permeability core that can be saturated under the square wave excitation are used to detect the weak magnetic field. Fluxgate current sensor uses the nonlinear relationship between magnetic induction intensity and magnetic field intensity of the magnetic core with high permeability in the measured magnetic field under saturation excitation of alternating magnetic field to measure the weak magnetic field. This physical phenomenon seems to be a "gate" for the measured environmental magnetic field. Through this "gate", the corresponding magnetic flux is modulated and induced electromotive force is generated. This phenomenon is used to measure the magnetic field generated by the current, thus achieving the purpose of measuring the current indirectly. In essence, fluxgate phenomenon is actually an associated phenomenon of transformer effect, also subject to the law of electromagnetic induction.

Fluxgate current sensing is realized through the classical control theory to detect the current, rather than through the conventional chip induction, is not sensitive to the external environment, basically no temperature drift and zero drift; Its magnetic core without opening cutting, small reluctance, high flux stability, sensor detection accuracy, high sensitivity, fast response speed. Therefore, the fluxgate current sensor with a precision of up to 10ppm is the most suitable for high-precision large current test and measurement.

High precision current sensor applications

1. Current measuring instrument

2, high precision stable flow source

3. (Gradient) amplifiers in nuclear magnetic resonance (MRI) : MRI requires precise, fast and controllable large currents

4, particle accelerator, constraint: these occasions need a strong, precise and stable magnetic field, which requires a stable large current. In this case, it is necessary to use multiple large current generators in parallel, and each current generator adopts high-precision AIT series current sensor.