|WikiProject Electrical engineering||(Rated Start-class, Mid-importance)|
Should include some information about Hall effect power sensors as seen here: http://www.allaboutcircuits.com/vol_2/chpt_12/3.html. Efadae (talk) 18:29, 7 April 2009 (UTC)
used for measuring power
wattmeter: it is an instrument used for measuring power. 188.8.131.52 19:48, 16 August 2006 (UTC)ADEEL ZUNAIR
digital electronic wattmeter/energy meter
This article has a lot of overlap with the Electricity meter article. That article has a lot of content. This article is barely more than a stub, and quite out of date.
A modern digital electronic wattmeter/energy meter samples the voltage and current thousands of times a second. The average of the instantaneous voltage multiplied by the current is the true power. The true power divided by the apparent Volt-Amps (VA) is the Power Factor. A computer circuit uses the sampled values to calculate RMS Voltage, RMS Current, VA, Power (Watts), Power Factor, and Kilowatt-Hours. The simple models display that information on LCD. More sophisticated models retain the information over an extended period of time, and can transmit it to field equipment or a central location.
There are currently (June 2007) two cheap digital models for consumers in the US: P4400 Kill A Watt by P3, and the EM100, for about $30. More expensive models are more accurate and/or have more features, such as using a price for electricity to compute and display the cost of using an applicance being measured/tested over a period of time.
Measuring RF power is an important but somewhat separate topic. It should be covered in this article, and/or linked to elsewhere.
The article should also discuss instruments meant for monitoring line-voltage loads (most common) vs. general-purpose instruments that cover a wider range of voltages and frequencies. -184.108.40.206 21:45, 12 June 2007 (UTC)
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" If the pressure coil has range of 300 volts, the half of it can be used so that the range becomes 150 volts."