Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1989-04-21
1990-11-20
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetometers
324255, G01R 3304
Patent
active
049721461
DESCRIPTION:
BRIEF SUMMARY
The invention is directed to a device for measuring an external magnetic field which is constant or varies over time, comprising at least one core consisting of a material having high permeability, a coil for the magnetization of this core via an alternating current source connected to the coil, and a measuring coil in which a voltage is induced corresponding to the magnetic field resulting in the coil produced by means of the applied alternating current and the external magnetic field to be measured.
Such a device is known from the DE-OS No. 33 45 712. In this known device, which serves particularly for measuring the direction of the earth's field, the core is saturation magnetized by means of an alternating current. In so doing, the degree of deviation between the period of the positive and negative half-waves of the measurement voltage forms a measure for the magnitude of the measured magnetic field in that, because of the external magnetic field to be measured, the core reaches the saturation region earlier in one magnetization direction and later in the other direction than it would without an external magnetic field. Accordingly, the measurement of the magnetic field can ultimately be reduced to a measurement of the pulse width repetition rate, i.e. the ratio of the period of the positive amplitude to the period of the negative amplitude, wherein the actual value of the magnetic field to be measured is derived from this pulse width repetition rate by means of a microcomputer.
In another known comparable device, the so-called "Foerster probe", the frequency spectrum is taken as criterion, which requires selective and expensive filters. The amplification is limited due to the filtering and various nonlinearities.
The invention has the object of constructing a device of the above mentioned type in such a way that a particularly high sensitivity is achieved, so that small changes in magnetic fields can be determined in particular.
SUMMARY OF THE INVENTION
This object is met, according to the invention, by means of an integrating device connected to the measuring coil, an arrangement for the subtraction of the direct current component or quasi-direct current component of the output voltage of the integrating device, and a device for detecting the maximum values of consecutive half-waves of the output signal (U.sub.x) of the subtraction arrangement.
In conformity with the prior art according to DE-OS No. 33 45 712, a distortion of the half-waves of the measurement voltage effected by means of the magnetization curve (hysteresis) and the steady field acting from the outside is investigated also in the solution according to the present invention. However, it is not the difference between the time points of the saturation magnetization which is derived from this distortion but, rather, by eliminating d.c. components the distortion of the measurement curves due to the external field itself, is determined. Since the measured signals contain no d.c. component, an extremely high sensitivity, which is limited only by the noise of the utilized amplifier, can be achieved by means of amplifying the integrated signal. This enables a wide measuring range and a high sensitivity at low cost. Moreover, one or more compensation coils can compensate for an external basic magnetic field such as the geomagnetic field in a relatively simple manner, so that very small relative changes in the magnetic field can also be determined in a particularly favorable manner as is desirable e.g. when used for sensors for moving metal parts or in the examination of soil in archeology or geology.
In a favorable embodiment form it is provided that a device for forming the difference of the maximum values of two consecutive half-waves comprises a switching device operating in dependence on the sign of the applied voltage, a sample-and-hold arrangement connected to every switching output of the switching device, and an adding device connected to the outputs of the sample-and-hold arrangement.
According to another advantageous embodiment form
REFERENCES:
patent: 3983475 (1976-09-01), Watanabe et al.
patent: 4007417 (1977-02-01), Takeuchi et al.
patent: 4290018 (1981-09-01), Rhodes
patent: 4303886 (1981-12-01), Rhodes
patent: 4305035 (1981-12-01), Mach et al.
patent: 4321536 (1982-03-01), Rhodes
patent: 4339727 (1982-07-01), Kage et al.
patent: 4677381 (1987-06-01), Geerlings
patent: 4733181 (1988-03-01), Bauer
Eckardt Dieter
Hettich Gerhard
Robert & Bosch GmbH
Strecker Gerard R.
Striker Michael J.
LandOfFree
Saturble core device with DC component elimination for measuring does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Saturble core device with DC component elimination for measuring, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Saturble core device with DC component elimination for measuring will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-456017