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AC and DC ground separation precision amplifiers.

Shrikant Lokhande
Intellectual 655 points

Hello all,

I have been designing a circuit for converting 0-36VAC signal to 0-10VDC signal by using precision amplifiers as shown in fig.

In this case I have to keep my AC and DC grounds common, which may cause problems during running condition as my AC signal is generated by a Tacho generator.

Tacho generator is held near Engine and may carry some noise so to avoid this I want to separate my AC and DC grounds.

Is there any simple method for this, please suggest.

Tacho o/p :  0 - 36 VAC,  0 - 240 HZ

Thanks and regards,

Shrikant

 

  • 0
    Genius 5430 points

    Shrikant;

    Preceding your circuit with a unity-gain difference amplifier may help. One input is connected to the tachometer output and the other input is connected to the tachometer ground. The CMR of the difference amplifier will reject tacho noise.

  • 0 in reply to Neil Albaugh
    Guru 21975 points

    Shrikant,

    I agree with Neil that a difference amplifier may help.

    You may also benefit from filtering prior to IC12a. A simple real pole of around 1kHz may be helpful. If you do not use a difference amplifier, a resistor of 100 ohms in series with the ground coming from the tachometer may help. Use this in conjunction with the R/C input filter.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Intellectual 655 points

    Hello Bruce and Neil,

     

    Thanks a lot for your quick reply.

    This will definitely help me in building a noise free circuit for tachometer.

     

    Thanks and regards,

    Shrikant