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### Topic: Amplifying Low Voltage AC signal (Read 780 times)previous topic - next topic

##### Oct 14, 2016, 05:40 pm
Hello!!

I have a vague idea how to solve this problem and I am looking for specific suggestions as I am from mechanical background.

I have a data acquisition system that can take minimum 100mV ac voltage. But my sensor generates a low voltage ac signal with maximum of 30mV peak to peak. So I am looking to amplify the signal before connecting my sensor to the data acquisition system.

In short, I am looking for suggestions or solutions on how to amplify a 0-30mV peak to peak ac signal to a minimum 100mV ac signal without altering the frequency.

Thank you

Regards

#1
##### Oct 14, 2016, 06:17 pmLast Edit: Oct 14, 2016, 06:21 pm by CrossRoads
You need an Op Amp.
Do you need it Arduino compatible (0-5V range),
http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/
- Add some gain and DC offset to make it 2.5V +/- your signal. Ex your .03V signal with a gain of 50 to make it +/- 1.5V, and add in DC of 0.05V on the 2nd input to make the output 2.5V +/- 1.5V.

Or do you just need it amplified (to -100mV to +100mV or more)? Same circuit can be used, just leave off the V2 input.
Dual power supply needed to allow +/- input & output.

Or use capacitive coupling with a single supply rail to rail output, see Figure 12 here:
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### MarkT

#2
##### Oct 14, 2016, 07:07 pm
Hello!!

I have a vague idea how to solve this problem and I am looking for specific suggestions as I am from mechanical background.

I have a data acquisition system that can take minimum 100mV ac voltage. But my sensor generates a low voltage ac signal with maximum of 30mV peak to peak. So I am looking to amplify the signal before connecting my sensor to the data acquisition system.

In short, I am looking for suggestions or solutions on how to amplify a 0-30mV peak to peak ac signal to a minimum 100mV ac signal without altering the frequency.
Do you mean -15mV to +15mV peak-to-peak or 0 to +30mV peak-to-peak?

What is the bandwidth of the signal?  What is the sample-rate of your data-acquisition system?
Perhaps you could tell us exactly which sensor this is?  And which data-acquisition system.

Also before replying check that this isn't an xy-problem: http://xyproblem.info/
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#3
##### Oct 14, 2016, 07:25 pm
Thanks for the replies guys. I appreciate your time.

Hey sorry for the confusion, it is -30 mv to +30 mV peak to peak.

The DAQ is NI SCXI 1102. Sampling rate is 300Hz.

Sensor is Omega FTB 1411 Flowmeter. It's a magnetic pick up sensor, which generates ac voltage.

Thank you.

#### MarkT

#4
##### Oct 14, 2016, 09:38 pm
If the sampling rate is 300Hz that will limit the highest pulse rate you can measure to below 150Hz (theoretical),
below 75Hz (in practice, or even lower).  Is that what you want?

Normal this sensor would be used with a pre-amp to give a square wave, and you'd use a pulse-rate
option for logging the rate.

Given the principle of operation it would be very instructive to see a 'scope trace of the signal itself
to work out how best to deal with it.
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