![]() Kilowattĭefinition: A kilowatt (symbol: kw) is a unit of power in the International System of Units (SI). The watt as a unit of power should not be confused with its energy counterpart, the watt-hour (and all its multiples/submultiples). The absolute watt was adopted as the SI unit of power in 1960.Ĭurrent use: As the SI derived unit of power, the watt in all its multiples and submultiples is used in many applications worldwide from radio transmission to use in the electric power industry. 1 absolute watt is equal to 1.00019 international watts. These were used until 1948 when the General Conference on Weights and Measures re-defined the watt to absolute units, using only mass, time, and length. In 1908, the "international" definitions were defined, with Siemens' definition being adopted as the international watt. It was first proposed in 1882 by William Siemens who defined it as "the power conveyed by a current of an Ampere through the difference of potential of a Volt." This was the definition used at the time within the existing system of units. History/origin: The watt is named after James Watt, a Scottish inventor. It is defined as 1 joule per second and is used to quantify the rate of energy transfer. Most instruments that display PFD units have actually measured the signal in terms of V/m and then internally calculated the equivalent (usually average) PFD value in W/m 2 or similar.Definition: A watt (Symbol: W) is the SI (International System of Units) derived unit of power. ![]() Powerwatch believes that the best unit of measurement for varying microwave signals at the non-thermal levels we are concerned with is volts per metre. ![]() The peak power of a DECT cordless phone base unit can be up to 100 times more than the average power This is because the normal max hold function on a meter gives you the maximum RMS value measured over the time you have been using the instrument, whereas peak detect measures the level at the top of any pulses in the signal.įor example, the peak power from a TETRA base station is twice the average power. Note this is not the same as a "max hold" facility. Some instruments have a "peak-detect" facility that can give the equivalent power as if the pulsing peak levels were continuous. Any PFD has to be integrated over time and most hand-held instruments average over at least a few seconds. The problem occurs because PFD is ONLY relevant to heating and it averages the power over time (6 minutes for official RF PFD measurements). This conversion is not particularly relevant for exposure from mobile phones, base stations and DECT cordless phones and the results can be extremely misleading. PFD = (V/m) 2/377 watts per metre squared (W/m 2)Į.g. ![]() These signals remain fairly constant in amplitude and the conversion from signal strength in volts/metre to power flux density (PFD) in watts per square metre can be done using the formula: For modern digital telecommunications signals, this is not as easy, or as useful, as you would first think that it would be.įor continuous-wave transmissions, including VHF FM radio signals, the conversion is relatively easy. Many people ask us for conversions between microwave measurement units so that they can compare the units we use, volts per metre (V/m), with watts per metre squared (W/m 2). Science index » Overview | Article library | List of studies | Basic guide to EMFs | International guidance levels | Unit conversion | Frequently asked questions | Other resources » Printer friendly version Conversion of RF units (V/m » W/m 2 and vice versa) ![]()
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