Patent No. 5256960 Portable dual band electromagnetic field radiation measurement apparatus

 

Patent No. 5256960

Portable dual band electromagnetic field radiation measurement apparatus (Novini, Oct 26, 1993)

Abstract

The invention discloses a magnetic field radiation monitor which comprises at least one sense coil adapted to sense magnetic flux from the electromagnetic field to be measured for both ELF and VLF type of fields. The sense coil is coupled to a detection circuit wherein an EMF generated in the sense coil will be amplified and frequency compensated in the circuit to give an extremely flat frequency response allowing accurate detection of complex magnetic fields. The circuit consists of an ELF and VLF stage, both selectively coupled to the sense coil and incorporated into the circuit by a user activated switch. The output of either the ELF or VLF stages is further processed and the output is provided to a display to indicate the magnetic field strength measured. The magnetic field radiation monitor may be calibrated to yield a true RMS measuring platform using a RMS detector circuit which will give an accurate indication of magnetic energy content for complex waveforms. An isotropic monitor may be provided where the configuration of the sense coil is designed to provide a non-directional magnetic sensor and appropriate detection circuitry to determine the total magnetic flux density detected by the magnetic sensor. The isotropic magnetic field radiation monitor will simplify use of the apparatus and will provide more accurate electromagnetic field measurements while maintaining the cost effectiveness of the apparatus.

Notes:  

Portable dual band electromagnetic field radiation measurement apparatus. Filed April 1991, granted October 1993. Device measures intensity levels of all frequencies contained in a complex electromagnetic field including pulsed fields. States that it measures Elf 1 - 1000 Hz and Vlf 10 - 500 KHz ranges. Adapted for the decimal place frequency measurements (.001, 6.26, etc) might aid in isolation of psychotronic frequencies.

BACKGROUND OF INVENTION

This invention generally relates to an apparatus for detecting and measuring low frequency pulsed/alternating magnetic fields to which a person may be exposed, and which may create a health hazard at high or continued exposure levels. More particularly, the invention relates to a magnetic and electric field radiation monitor which is compact and easily used to allow the device to be easily carried to various locations and environments in which a person may be exposed to such radiation. The monitor allows the detection and the measurement of magnetic and electric fields emitted from various electronic equipment and the like, such that the location and strength of the fields may be determined to allow reduction of personal exposure to such fields.

Recently, the effects of pulsed/alternating magnetic fields emitted from such things as video display terminals (VDT's), television receivers, microwave ovens, power lines or a variety of other devices which emit pulsed/alternating magnetic fields, have been linked to increased health risks for persons exposed to such fields. The potentially harmful health effects of electromagnetic emissions from this various electronic equipment include an increased risk of developing cancer, risks of birth defects and miscarriages in pregnant women, and other health hazards. The evidence of such health risks has been increasing dramatically within the last few years, and recognition of the problem is slowly being acknowledged within the industry and community. The epidemiological evidence being gathered on the hazardous effects of electromagnetic fields given off by various electronic equipment has been mounting. This evidence has led to various responses initiated by manufacturers of equipment emitting potentially harmful electromagnetic radiation, as well as by governmental authorities who have imposed restrictions upon emissions from various equipment to minimize the risk posed thereby. Various editorials and articles provide general background information on the potential risks of the low frequency pulsed/alternating magnetic fields emitted from various electronic equipment, such as found in MACWORLD, July 1990 issue at page 136, POPULAR MECHANICS, November 1990 issue at page 110 as well as others. Although these articles have raised the public awareness about the possible dangers of low frequency electromagnetic fields or radiation, the industry has not yet responded in an adequate fashion to provide individual protection to the user of such equipment.

The magnetic fields which are deemed a potential health hazard are normally generated from power lines and other high-voltage electrical apparatus, which emit extremely low frequency (ELF) magnetic fields in the 50-1000 Hz range, as well as the higher frequencies termed very low frequency (VLF) emissions in the range of 10-500 KHz. As an example, the ELF magnetic fields emitted by video display monitors were tested as described in the MACWORLD article mentioned hereinbefore, magnetic field emissions were measured at various distances from all portions of various monitors. It was found that the strongest emissions from video display terminals are at the sides and tops of the monitors, wherein the field strength may be as much as 70 milligauss (mG) at a distance of 4" from these areas. Field strengths at the front of the VDT were over 22 mG at the same distance, but at a longer distance such as 28" from the front of the VDT, the emissions dropped to below 1 mG. Although this generalized information would indicate that keeping a safe distance from a VDT or other electromagnetic radiator may minimize the harm of such fields, for any particular environment in which a person may be placed, the exact location and field strength of magnetic field radiation may not be generally surmised. It is also noted that the magnetic field radiation from such electromagnetic radiators may not be shielded by simple shielding structures, and therefore other means must be utilized to minimize emissions from such equipment. Various attempts have been suggested for minimizing the actual emission of pulsed/alternating magnetic fields from such devices, such as a compensating coil placed in a VDT or the like which produces lines of magnetic flux moving in opposition to those generated from the CRT's deflection coil. Also, LCD or electroluminescent displays have been found to emit negligible magnetic fields, and may be resorted to minimize emissions, but such equipment is higher in cost and does not provide similar performance characteristics as CRT technology.

Although the approach of minimizing the emissions from such equipment will be a necessary step to minimize the risk associated with use of such equipment, there is a critical need to provide an individual with the ability to monitor and measure possible emissions of magnetic field radiation so that they themselves may minimize the potential risk of exposure to such fields by positioning themselves to eliminate or minimize such exposure Various types of electromagnetic field measurement apparatus are available, for example, a VDT/VLF Radiation Survey Meter Model HI-3603, which is stated to measure electromagnetic field strengths in the frequency range from 10 KHz to 300 KHz, and an ELF/Power Frequency EMF Survey Meter Model HI-3604 designed to evaluate electric and magnetic fields associated with 50/60 Hz power lines and the like, both manufactured by Holaday Industries, Inc. Another apparatus for electromagnetic field radiation measurement is a digital display field monitor model ELF-50D produced by Walker Scientific Inc., which is a portable, hand-held instrument designed and calibrated to measure low level 50 Hz or 60 Hz electromagnetic field radiation. These and other companies also produce a variety of other gaussmeters, magnetometers and fluxmeters for magnetic field measurement in a variety of different applications including nuclear magnetic resonance applications and other industrial applications.

Generally, these types of instruments as manufactured by these and other companies are designed as laboratory or industrial measurement tools rather than for use by the general public. Such equipment is limited in its application for use by the general consumer as the cost of such instruments are high and therefore impractical and generally unavailable to the individual. Additionally, many of these devices are operationally complex, and again generally unusable by the individual. Various other lower cost devices have been introduced, such as the Walker Scientific Model ELF-50D, which is a portable, hand-held unit and of lower cost, but which is calibrated for a fundamental frequency only and therefore limited to a single frequency response. Any devices of similar type generally suffer from limited or single frequency response, which will prevent the user from achieving a complete or accurate measurement of magnetic fields of a complex nature typically emitted from video display terminals, television receivers and the like. Additionally, such instruments are again difficult in their use to obtain accurate and valid quantitative measurements of magnetic field radiation. Similarly, electric field measurements are desirable in many situations, and accurate field measurements have not been generally achievable with a low cost, easily used device.

SUMMARY OF THE INVENTION

Based upon the foregoing, there has been found a need to provide a personal magnetic or electric field monitor which is low cost, easy to use and will effectively and accurately measure complex electromagnetic and electric fields. It is therefore a main object of the invention to provide a magnetic and electric field radiation monitor which is portable and easily used, and may be manufactured at a low cost so as to be accessible to an individual consumer.

Another object of the invention is to provide a magnetic field radiation monitor which may be used to accurately measure both ELF and VLF pulsed/alternating magnetic fields over a broad frequency spectrum.

Yet another object of the invention is to provide a radiation monitor which is adapted to detect and measure non-ionizing radiation to quantitatively analyze an environment where the potential hazard of pulsed/alternating magnetic fields exists to provide an immediate indication of the magnitude of electromagnetic field radiation to enable the user to avoid exposure to such fields.

Another object of the invention is to provide a magnetic field radiation monitor which utilizes a uniquely designed sense coil which is simple and cost effective in its manufacture, and an associated detection circuit which provides a relatively flat frequency response over a broad frequency bandwidth to enable accurate detection and measurement of complex electromagnetic fields.

Still another object of the invention is to provide an isotropic field radiation measurement device which will simplify use of the device and increase the detection accuracy thereof.

These and other objects and advantages of the invention are accomplished by a radiation monitor which comprises at least one sense coil adapted to sense magnetic flux from the electromagnetic field to be measured for both the ELF and VLF type of fields. The sense coil is coupled to a detection circuit wherein an EMF generated in the sense coil will be amplified and frequency compensated in the circuit. Amplification and frequency compensation may be accomplished by a precision operational amplifier having a feedback loop designed such that the voltage gain of the operational amplifier stage has an output response which is exactly the opposite of the output of the sense coil to yield a relatively flat frequency response. Further amplification may be provided to achieve the proper gain in the circuit. The circuit consists of an ELF and VLF stage, both selectively coupled to the sense coil and incorporated into the circuit by a user activated switch. The ELF and VLF stages are similar in many respects, but the VLF stage includes a frequency filter to shape the frequency response thereof, for rejection signals outside of the desired frequency range. The output of either the ELF or VLF stages may be coupled to a precision rectifier circuit to provide full-wave rectification of the signals to insure accuracy of signal interpretation across a wide signal level range. The frequency response of the precision rectifier circuit will be broad enough to accommodate both the ELF and VLF range, thereby minimizing circuit components and complexity. Further signal processing is then performed and the output is provided to a display to indicate the magnetic field strength measured. The magnetic field radiation monitor may be calibrated to yield RMS indications for non-complex signals and average indications for complex signals. Further processing in the circuit may include an RMS detector circuit which will give an accurate indication of magnetic energy content for complex wave forms. An isotropic monitor may be provided where the configuration of the sense coil is designed to provide a non-directional magnetic sensor and appropriate detection circuitry to determine the total magnetic flux density detected by the magnetic sensor. The isotropic magnetic field radiation monitor will simplify use of the apparatus and will provide more accurate electromagnetic field measurements while maintaining the cost effectiveness of the apparatus.

--------------------------------------------

While preferred embodiments of the invention have been described herein, it will occur to those skilled in the art that a variety of changes or modifications can be made. The various components of the measurement circuits herein may be modified to some degree while maintaining the desired characteristics thereof. A fully integrated circuit design is desired, which has been found to be quite cost-effective. The magnetic field radiation monitor provides an indication of the power content of a magnetic field and not the peak value thereof, eliminates the frequency dependency of a sense coil and allows true and accurate measurements of both ELF and VLF signals. It is also noted that in the isotropic embodiment of the invention, the conversion of the filtered AC signal to a direct current value may not be necessary as the AC waveform could be adequately sampled in an A to D conversion and subsequently processed by the microprocessor 190. The conversion of the AC signal to a digital value also would enable the field strength to be interpreted in several different ways including peak detection, average detection, RMS detection, the rate of change of the magnetic field or the like. Alternatively, the instrument could be programmed to take measurements at predetermined times of day and store the information for retrieval at a later time or may be fed directly to a remote computer to continuously monitor a particular environment and enable unattended operation of the meter. The microcontrolled isotropic principles as set forth in the invention may also be applied to electric field measurements wherein the remote unattended operation of an electric field monitor will eliminate the possible adverse effects of a human body close to the instrument at the time of measurement. Accurate electric field measurements may also be obtained using some of the advantages of the monitor herein. It is apparent that a wide variety of modifications could be made without departing from the spirit and scope of the invention as defined in the appended claims.