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Possible Duplicate:
ICs that convert an AC signal into its true rms value

Can anybody please recommend me a current transducer which has the provision of true RMS voltage output and instantaneous voltage output. The measuring range is 0 to +-160A and has a supply voltage of +-15V. Basically I am looking for a replacement for LTA 50PR/ LTA 100PR. (http://www.farnell.com/datasheets/96665.pdf) here
These transducers are no more in production.

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  • \$\begingroup\$ This very much overlaps your question asked 30 minutes earlier. Please combine the two. is essentially identical to your question posted about 30 minutes earlier. Please combine the two. \$\endgroup\$ – Russell McMahon Mar 6 '12 at 12:12
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Any RMS converter that meets your accuracy spec and that has an averaging period of 200 mS will meet your requirement. See below.

In the datasheet here note that it says "averaging time constant: 200 milliseconds.
This means that

  • it calculates the RMS value of the AC signal for 200 milliseconds and outputs it as a DC RMS value.

  • it then calculates the RMS value for another 200 mS period and outputs it.

IF the periods are sequential and non overlapping the output changes every 200 MS or less.

BUT if this was a digital system they may sample every mS, take 200 samples at t= 1mS to t = 200 mS, then calculate the RMS value for the 200 samples and output it.
One mS later they may take a sample for t=201 mS and throw away sample for t=1 MS and calculate the RMS value for periot 1 - 201 and output it.

Note that If a repeating (periodic) waveform signal with period of 200 mS or a factor of 200 mS (100, 50, 40, 25, 20, 10, 5, 4, 2, 1, ... mS) THEN the output value would be steady DC.

Note that if the input signal was a repeating waveform with period NOT equal to 200 mS or a factor thereof then the output will fluctuate and the variatiins will be meaningless for practical purposes.

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