How Fluxmeters, sense coils and voltage integrators work
Fluxmeters: more than a century of applications
Moving a coil in a magnetic field induces a voltage proportional to the change in The magnetic flux density, B, integrated over an area. The voltage induced in a coil is proportional to the flux... More seen by the coil. Similarly, a varying field induces a voltage on a stationary coil. These principles have been understood and exploited since the 19th century to precisely measure, for example, the earth’s magnetic field. Fluxmeters also continue to play an important role in the measurement of the hysteresis of magnetic materials and in magnet design, for example to determine the losses in a A way of thinking about magnetic systems, similar to an electric circuit. Allows predicting, for example, the flux density in... More.
A coil: the most flexible of all magnetic probes
The use of coils is limited only by the imagination. How do you measure the The magnetic flux density, B, integrated over an area. The voltage induced in a coil is proportional to the flux... More density inside a solid piece of iron? Certainly not with a Hall sensor – try a Before being able to measure, an NMR teslameter has to search the range of the probe to find the NMR... More coil tightly wrapped around the block. How about the field induced by an MRI In this context, gradient refers to the spatial variation of the magnetic field. More coil, with frequencies in the MHz The range of a probe is defined by the minimum and maximum field strength it can measure. On an instrument,... More? Again, you’ll have better luck with a single turn of wire than with the most elaborate Hall instrument.
Since the voltage induced on the coil is proportional to the The magnetic flux density, B, integrated over an area. The voltage induced in a coil is proportional to the flux... More change, we need to integrate the voltage to obtain the change in The magnetic flux density, B, integrated over an area. The voltage induced in a coil is proportional to the flux... More:
There are two commonly used approaches to building an The part of a fluxmeter that integrates the voltage More; each has its limitations:
- A A standard is the internationally agreed-upon physical representation of a unit. For example, a caesium clock is the standard for... More analogue The part of a fluxmeter that integrates the voltage More circuit, using a high-gain amplifier with a capacitive feedback. The low-end bandwidth is limited by the size of the capacitor, and there are numerous analogue noise sources, such as leakage currents and temperature dependence. In addition, we usually want a digital result, so we have to digitize the output anyway.
- Digitize the voltage at periodic intervals and perform a numerical integration. This method has to limit the high-end bandwidth to satisfy the Nyquist criterion, it depends critically upon the linearity of the ADC, and can suffer from quantification noise.
The magnetic The magnetic flux density, B, integrated over an area. The voltage induced in a coil is proportional to the flux... More is defined as the integral of the field strength B over the area of the coil A:
If the field strength is constant over the area of the coil, the integrated voltage gives the change in field strength B:
where A is the effective area of the coil and theta is the angle between the coil’s axis and the field. To precisely measure magnetic field strengths with a An instrument that measures flux changes by integrating the voltage induced on a coil. More, it is therefore essential to know the effective area of the coil with a great deal of Precision is how closely multiple measurements will be clustered. Also called reproducibility or repeatability. In everyday speech, often confused with... More. This is usually achieved by calibrating the coil in a known magnetic field. For measurements with 100 Parts per million, or 10-6. Bigger than a ppb, but still pretty darn small. More or better Precision is how closely multiple measurements will be clustered. Also called reproducibility or repeatability. In everyday speech, often confused with... More, this requires an NMR-controlled or -stabilized A magnet used for calibrating a magnetometer. Reference magnets are often controlled or even regulated by an NMR teslameter. More.
FDI2056 Fast Digital Integrator
The first off-the shelf instrument to quantify magnetic field transients
The process of measuring magnetic field intensity at many different points, in order to understand the structure of the field... More Particle accelerators were developed by physicists to study the elementary nature of matter. Nowadays, they are usually immense, highly international... More magnets
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