Magnetic field camera
A magnetic field camera is a sensor system that records the flux density of a magnetic field within a flat surface and visualizes it - in real time or as a snapshot. Flat magnetic field sensors or those that consist of several small sensors arranged as an array are used. These are introduced into the magnetic field to be measured, the measured electrical signals are digitized and graphically displayed. There are also magneto-optical sensors which directly emit magnetic fields from flat surfaces - e.g. B. by changing the polarization of light in a transparent material - make it visible.
If the magnetic field is only recorded along a line, it is called a "magnetic line camera". This is sufficient for some applications and faster due to the smaller number of measuring points.
Operating principles
The function of current magnetic field cameras is based on one of two different physical effects:
In Hall sensors, a magnetic field generates a voltage signal proportional to its flux density in an electrically (semi-) conductive, flat Hall sensor . A flat array of Hall sensors, also called Hall elements, supplies electrical signals that are digitized and visualized after appropriate processing (see picture on the right).
There are different technological forms of this approach.
On the one hand, a uniaxially measuring camera with very high resolution (approx. 50 micrometers) over an area of approx. 1.7 cm 2 was developed, which consists of an integrated circuit with 128 • 128 classic lateral Hall elements, which form the flux density component B. Measure z perpendicular to the chip surface over an area of 13 • 13 mm.
On the other hand, cameras measuring three axes are being developed, which can measure very quickly (approx. 6 ms for an image) over a large observation area (up to 15 cm) and which consist of arrays of discrete, integrated 3D Hall sensors that contain all three flux density components (B x , B y and B z ). Another special variant is the so-called line camera with which the magnetic field can also be measured inside bores or in the interior of ring magnets.
Since the measurement result is available in electronic form in all cases, such magnetic field images can also be processed further and / or stored on digital storage media without any problems. In principle, a three-axis measuring magnetic field camera can also be implemented with discrete magnetic field sensors (one sensor for each axis).
In flat, translucent magneto-optical sensors , the polarization axis of the light is rotated by a magnetic field and flat light / dark information is obtained using a polarization filter (as an analyzer), which is a direct image of the causing magnetic field component perpendicular to the sensor. It is, so to speak, a single-axis magnetic field camera.
In principle, an optical visualization would already be provided here, but the contrasts with small magnetic fields are too low to be perceived by the human eye. That is why the flat light / dark image is digitized with a high-resolution optical camera and then processed electronically so that weaker magnetic fields are also visible.
The special feature of this technology is the large observation area of several centimeters, which is only limited by the production limits, with a very high spatial resolution at the same time. The main application is in quality inspection, since structures with magnetic scales and codes, but also local magnetization errors and superficial material cracks can be recognized very well. However, due to the comparatively low sensitivity, it requires a very small distance to and a very flat surface on the measurement object.
Applications
In general, these cameras are used wherever the evaluation and visualization of magnetic fields are important. Examples are:
- Quality assurance in the manufacture of permanent magnets
- Measurement of stray fields on motors and other magnetic actuators
- Development of magnetic position / angle measurement systems
- Characterization of permanent magnets and electromagnets
- Assessment of solar cells, batteries / accumulators or electrical circuits using a functional magnetic fingerprint
Individual evidence
- ↑ Magcam MagCam manufacturer website
- ↑ HallinSight product sheet. Retrieved March 14, 2019 .
- ↑ Discrete realization Vector magnetic field camera for permanent magnets inspection
- ↑ MagView manufacturer / sales
- ↑ Article on how MagView works
- ↑ DENKweit manufacturer / sales, product: B-TECH