AC signal conditioning

[jjmcousineau]

ac signal conditioning

I was wondering if anyone could point me to some good referances on how to attentuate an AC signal (120/240v 60hz) down to managable levels for reading with a ADC. The ADC will likely be 0-5v input. I was looking at using opamps to attenuate but would appreciate some direction.

Thank you.

 

[IanP]

If you need isolation then an isolation step-down transformer (120/240-to-5) is a good option ..

If you don't need isolation try to design a simple 2-resistor voltage divider ..
Below is an example of an input of a digital voltmeter with voltage selector ..

Regards,
IanP

 

[jjmcousineau]

I was just wondering what is the purpose of the two opposing zener diodes just after the 1M resistor?

 

[IanP]

This combination works as AC voltage limiter:

For positive signals, the clip level begins at

V LIM POS = Vf D1 + VZ D2 = 0.7V + 5.1V ≈ +5.8V

where Vf D1 is the forward diode voltage of D1 and VZ D2 is the zener voltage of D2. Likewise, the negative clip level is set at

V LIM NEG = - ( Vf D2 + VZ D1 ) ≈ -5.8V

Above these levels the diodes conduct, clamping the output voltage to the same level.


Regards,
IanP