Amplification of AC signal

[hamadsultan]

Hi Friends;
I make a frequency counter 10 to 999 HZ. Power supply is 12 v dc.
The amplitude of incomming signal is only 0.5 volt from the turbine flow meter.
But the circuit trigger at above 2.0 volt. Now i want to amplify the signal from 0.5 volt to 3 or more volts to read the frequency. I need help which opamp and in which configration i used.
I try inverting and non inverting both by using LF353 but unable to amplify the signal.
please guide me how i amplify the signal?
Best regards
Hamad

 

[kabiru]

For that i suggest you use TTL logic buffer,it can deliver up to 5v.

 

[keith1200rs]

A logic buffer will not amplify low level analog signals. An opamp is the easiest way. Post the circuit of what you tried so we can fix it.

Keith

 

[kabiru]

What if the analog signal is rectified to dc? The circute can be triggered with 5v therefore if the signal can be converted from 0.5v Ac to Dc I think it should work by applying the Dc signal at the gate of the logic buffer,an op-amp should also work if connected as amplifier.

 

[chuckey]

It is difficult to rectify .5V ac. If you can not get an op amp circuit going, it is very difficult to proceed with any alternative paths.
Frank

 

[alexan_e]

Use the attached schematic, gain is (R2/R3)+1
in my schematic it is (9/1)+1=10
R1 is just in input load resistor, you can remove it if it not needed.



CORRECTION this works for DC pulses, if you have actual AC you need to use symmetric power supply, or a bias in the input.

Are you sure that the signal you have is actually swinging below 0 (negative voltage)?

Alex

 

[RK_ELECTRONICS]

hi friends
1. the o/p of turbine is ac, hence first convert in to dc.
2. the voltage less than .7 can not rectify with diode , so you need to use op-amp as precise rectifier. you can get the circuit on books or internet.
3. after rectify your low level signal , amplify it by op-amp amplifier by choosing the right values of Rf and Ri resistors.
4. apply the o/p of amplifier to your counter.

 

[hamadsultan]

Hi friends;
If i convert it into Dc how i read the frequency?
I explain again that the output of turbine typr flow meter have a frequency 10 to 999 HZ depends on the flow of gas. Its amplitude is 0.5 volt i am not sure what type of waveform it generated but not pure sinosidal.
I have a three digit frequency counter which starts or trigger to read the frequency at 3 volt. I check it with apply a signal through signal generator when i apply a 300 hz at 2.0 volt its read nothing when i just increase the amplitude to 3 volt it reads 300 hz exactly.
Now i want to just amplify the input signal which comes from turbine type flow meter from 0.5 to 3 volt. How i fix it?
One person advise me use optocupler is it possible that LED trigger at 0.5 volt?
Please guide me how i amplify the signal from 0.5 to 3 volt. The VCC is used 12 volt for other ICs and display.
Best regards
Hamad

 

[kabiru]

I now understand what you are saying,to do that you need to used the op-amp and if you want to used the optocopler then you have to refer to it's datasheet,if the minimum input signal is within the range then it can be used.

 

[keith1200rs]

I guess something like this would do. You need to pick a suitable rail-rail opamp - I just threw one on there. You may need to AC couple the output.

Keith.

 

[RK_ELECTRONICS]

hi hamadsultan,

you do not understand what i am saying. turbine type flow meter has almost sin wave. if u use a non-inverting op-rectifier (half wave), you will get pulses equal to frequency (as 50 hz ac produce 50 +ve pulse after rectify by half wave rectifier).then amplify these pulses by op-amp ampr to threshold level.these amplify pulses can be count easily.

you can do this with a single ic as lm317 or any quad op-amp ic.
non invertig rectifier ckt as given

o/p waveform


then amplfy by the ckt below