To get an RMS value when you cant afford the time it takes to heat an element, try this technique. It may not be feasible for a multimeter but how about a sampling voltmeter good up to 600 kHz?
Mathematically, the RMS value of a function is obtained by squaring the function, averaging it over a time period I` and then taking the square root:
Vrms = root of (1/T integrated from 0 to t * V^2dt)
ln a practical sense this same technique can also be used to find the RMS value of a waveform. Using two multipliers and a pair of op amps, an RMS detector can be constructed. The first multiplier is used to square ts. input waveform. Since the output of the multiplier is a current, an op amp is customarily used to convert this output to a voltage. The same op amp may also be used to perform the averaging function by placing a capacitor in the feedback path. The 1 second op amp is used with· a multiplier as the feedback element to produce the square root configuration. This method eliminates the thermal-response time that is prevalent in most RMS measuring circuits. The input voltage range for this circuit is from 2 to 10 Vpk. For other ranges, input scaling can be used. Since the input is dc coupled, the output voltage includes the dc components of the input waveform.
Mathematically, the RMS value of a function is obtained by squaring the function, averaging it over a time period I` and then taking the square root:
Vrms = root of (1/T integrated from 0 to t * V^2dt)
ln a practical sense this same technique can also be used to find the RMS value of a waveform. Using two multipliers and a pair of op amps, an RMS detector can be constructed. The first multiplier is used to square ts. input waveform. Since the output of the multiplier is a current, an op amp is customarily used to convert this output to a voltage. The same op amp may also be used to perform the averaging function by placing a capacitor in the feedback path. The 1 second op amp is used with· a multiplier as the feedback element to produce the square root configuration. This method eliminates the thermal-response time that is prevalent in most RMS measuring circuits. The input voltage range for this circuit is from 2 to 10 Vpk. For other ranges, input scaling can be used. Since the input is dc coupled, the output voltage includes the dc components of the input waveform.
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