Any good Vrms to Vdc converter

[Angelo]

For a project where I need to measure an inductor (detection loop) at 60kHz, I plan to use RMS to DC converters: one to measure voltage across de inductor, and one to measure current across a sense resistor.
Then measure phase between voltage and current with two zero crossing detectors to generate digital pulses.
L is the easy to calculate and display.

Is there any good device for RMS to DC conversion ? Idealy a model with evaluation board, to be used for the prototyping phase.

Thanks for any tips

Angelo

 

[PaulS]

I tend to use Google Gemini (the one that shows as the "AI Mode" button in the Google Chrome browser) as a starting point for this kind of research.
Gave it your complete question, and this is what it came back with: https://share.google/aimode/BTSTkZvatyzXHLvOZ . Perhaps helpful?

Paul

 

[MarkT]

Vrms is the same as Vdc for power dissipation in a resistor - you are effectively wanting to synthesize a single-ended low-bandwidth signal with same power level. To convert an AC signal to a DC signal with the same Vrms as Vdc involves using an analog multiplier, low-pass-filtering and then analog square-root conversion!
These days it would be done in software using an ADC and a DAC. You also need to worry about whether to count DC offsets on the AC signal or not.

This seems like xy-problem territory - simply send both AC signals to ADCs and do the analysis in the digital domain directly.

If you know you have sinusoidal waveforms only you can simply use a peak-measuring circuit or a precision rectifier to get a DC voltage in the analog domain. This is much simpler than true-rms.

 

[IleanaZang]

For a project where I need to measure an inductor (detection loop) at 60kHz, I plan to use RMS to DC converters: one to measure voltage across de inductor, and one to measure current across a sense resistor.
Then measure phase between voltage and current with two zero crossing detectors to generate digital pulses.
L is the easy to calculate and display.

Is there any good device for RMS to DC conversion ? Idealy a model with evaluation board, to be used for the prototyping phase.

Thanks for any tips

Angelo

For a VRMS-to-VDC converter, I would focus on the input waveform, required accuracy, response time, and how much filtering is acceptable. It is also worth checking how the circuit behaves with changing frequency and load. FT4232H-56Q-REEL is more relevant to USB-to-multi-channel serial applications, so I would keep that separate from the converter design.

The AD8436 from Analog Devices looks like a good fit for this. It is a true RMS-to-DC converter with a 1 MHz small-signal bandwidth, and ADI specifies about 65 kHz for 1% additional error, so it should be worth considering for your 60 kHz measurement. There is also an EVAL-AD8436 evaluation board, which could be useful for prototyping. The older AD736 also has an evaluation board, but its bandwidth is less suitable at 60 kHz.