Electromagnetic Field Measurement Probe

2016-01-28 07:32  
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The circuit was aimed to measure the variation in magnetic and electric fields by designing an electromagnetic probe with a headphone socket and an output meter.

Electromagnetic Field (EMF) – a physical force fields produced by electrically charged particles or objectsLF351 – a wide bandwidth singleJFEToperational amplifier with high slew rate, operation without latch up, compensated internal frequency, high input impedanceJFETinput stage, protection for output short circuit, low offset current and input bias, wide common-mode and differential voltage range, low power consumption, and adjustable internal input voltageBC109C – an epitaxialNPNsilicon planar transistor having the collector electrically connected to the TO 18 metal case

Both audio and RF signals with a frequency range around 100 kHz can be detected as well as the lost electromagnetic fields. The circuit can identify metal wiring if it is carrying AC current but it will not serve as a metal detector. Since the gain is being revolved by the input capacitance of the probe cable, the gain of the op-amp, and 150 pF capacitor, the frequency response of the circuit ranges from 50 Hz to around 10 kHz. The audio frequencies may be monitored by the headphones when inserted to the socket. The probe can be constructed from a radial type inductor having a screen cable length of 50 cm passing through a pen tube. If needed, a plug and socket may be used by the probe cable.

To test the circuit operation, the windings of a small transformer can be applied with an audio signal, using an audio signal generator, to produce electromagnetic field for easy detection of the probe. On the other hand, the probe can be placed near an electrical device, mains wiring, or a power supply in the absence of a signal generator. This will however, produce sound in the headphone and cause a deflection on the meter if the frequency is no more than 15 kHz. The circuit is being powered by a 9 V battery source.

The probe is moved around while the circuit is switched ON and a headset can be optionally plugged. An indication can be seen on the meter especially if near any electrical equipment which automatically produces a hum. The circuit should not be placed near any transformer as it can cause significant mains hum or noise. The proper positioning of the tester should be less than the diameter of the transformer. Nevertheless, there are toroidal transformers that are designed with less hum field. Calibration may also be required for the probe depending on the design and specifications. The calibration shall be based on frequency response, accuracy, amplitude response, linearity, isotropy, response to signal modulation, response time, and time constant.

Other designs of electromagnetic field measurement probe consist of an antenna arrangement for detecting electromagnetic field. This will produce a corresponding electrical output. Along with this is an output connector arrangement to provide the corresponding electrical output of the antenna arrangement to a measurement probe output of the probe. This circuit will then be enclosed in a dielectric material with low permittivity.

Electromagnetic field may be discovered in electric razors and hair dryers, telephones and answering machines, microwave ovens and radars, fluorescent lights, electric clocks, electric blankets and waterbeds, computers, home wiring, transformers, substations, and power lines. In many areas of industry, they develop the properties of electromagnetic field to be more useful. It was established in various fields like the X-rays which are high frequency electromagnetic radiation and are utilized in radiometry in telecommunications, in radiography in medicine, in laser therapy in medical, and in radio astronomy. Laser application can be found in devices like CD players, barcode readers, and in military devices like the laser-guided bombs. Moreover, electromagnetic field can be used in electrical relays to trigger or retrigger the two output states.

The LF351 op-amp may be used in applications such as high speed integrators, sample and hold circuits, fast D/A converters, and other circuits requiring wide bandwidth, high slew rate, high input impedance, low noise, low input bias current and low input offset voltage drift. For maximum current supply, the LF351 is strongly preferred but for devices with critical requirements, the LF356 is used.

The electromagnetic field probe may be used to monitor personal RF radiation, to measure electromagnetic field interference in electronic equipment, in vivo measurement of RF fields, in determining the safe radio frequency (RF) radiation levels by measuring microwave fields, and in mapping microwave antenna patterns, and measurements during the treatment of tumors.

Source:www.zen22142.zen.co.uk/Circuits/Testgear/emmeter.htm


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