# Voltage Variation Sensing

#### primer101

Joined Nov 24, 2019
4
Hello everybody, using a PIC 8 bit, I need to sense the voltage variation at the output of a position transmitter with the intention of plot it vs position using a PC, the signal is ±4 V 400 HZ, the variation from the initial position to full stroke is about 1.5 to 3.5 Vrms. I am getting a sample of the signal using the ADC module, but I need the Vrms or an average voltage. How can I do it? How can I condition the signal? Should convert the signal to DC?, How can I convert the signal to DC while maintaining it proportional to the variations of the input signal. Thanks for your help and time.

#### ericgibbs

Joined Jan 29, 2010
14,126
hi 101,
Have you considered a precision rectifier.?
E

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#### wayneh

Joined Sep 9, 2010
17,153
If I understand correctly, you could use a low pass filter to tease out the DC component of the AC signal. But I also think you could get what you need by using a proper sampling scheme. For instance if you sample 20 times over half a second and average those 20 samples, it ought to be awfully close. There's probably a more elegant approach but you get the idea.

#### Wolframore

Joined Jan 21, 2019
2,380
the opamp rectifier is a good solution and frequency is low enough to get great results using just about any opamp. You can do the averaging in the microcontroller. Is it a sine wave? If it's square wave you should be able to use peak values.

#### primer101

Joined Nov 24, 2019
4
Thanks everybody. The signal is a sine wave 400 Hz. I am getting >2000 samples/sec of 10 bit in the PC ready to process. The requirements are the signal level change should not exceed 15 mV within 0.2% of the total travel. I am thinking to fully rectify the signal and calculate the average, and this should be proportional to the level of the signal, so I can plot the average vs position and determine the distorsion.

#### ericgibbs

Joined Jan 29, 2010
14,126
hi,
If you have a circuit design please post and we can check it out by using a LTSpice simulattion.
E