Moving Charge Sensor of J. Ahern


Posted on Feb 6, 2014

An inexpensive electronic instrument useful in demonstrating electrostatic phenomena. First, Ahern`s instrument can be employed as an inexpensive and effective substitute for the tonal electrostatic voltmeter. Second, the instrument provides polarity-dependent information about electric charge motion that other, more conventional instruments do not provide. Third, this apparatus is a very easily built electronic-based


Moving Charge Sensor of J. Ahern
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instrument for monitoring static charge. What distinguishes Ahern`s instrument from other charge detection and measurement apparatuses used in electrostatics demonstrations, such as the conventional leaf electroscope and the tonal electrostatic voltmeter, is that Ahern`s device responds to the movement of positive (+) and negative (-) electric charge toward or away from a sensing electrode. As such, the instrument is probably most closely akin to some of the electrostatic charge monitors now commercially available and routinely installed in electronics assembly areas to detect conditions that might cause damage to sensitive electronics components during assembly. The instrument is small and portable, it operates on a 9 volt battery, and the output is visual. Furthermore, its construction requires only minimal skills with a soldering iron and other simple tools, and it can be packaged very conveniently in a small, shielded box. Refer to the photo at the left. A short, telescoping cellular telephone antenna mounted so that it retracts into the box when not in use, serves as a sensing electrode. The instrument is sensitive primarily to the movement of charge rather than to its presence. Thus, when the approach of negative charge is sensed, the green LED comes on, while the red LED lights if positive charge is approaching. As negative charge starts to recede from the sensing electrode, the green changes to red, while red...




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