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Appropriate DAC

Discussion in 'General Electronics Discussion' started by Chaotikmind, Jan 11, 2016.

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  1. Chaotikmind

    Chaotikmind

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    Jan 11, 2016
    Hi,
    i'm currently making a circuit to sample & control an old Ometron vibrometer
    the point is i need a +/-5V signal output to control the actuators, and i have trouble finding one matching that

    should i stick with a DAC like the DAC5687, and fix the voltage output, or would it be better to find one which ouput +-5v directly?
     
  2. Martaine2005

    Martaine2005

    2,933
    800
    May 12, 2015
    Hello,
    Have you tried Linear Technologies 'Voltage Output DAC search'?
    Input your requirements and see what is suggested.

    Martin
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    On the other hand it is no magic at all to use any DAC that basically fits your needs (resolution, speed, price) and adapt the output voltage range by a little operational amplifier circuit (adjust offset and gain to fit any range you need)
     
  4. Chaotikmind

    Chaotikmind

    3
    0
    Jan 11, 2016
    Yes, i guess you're right, i'm just concerned by noise in general, wouldn't it be better if the dac has the right range from the beginning ?
    i mean if i put an actuator in a position, it would be nice if i can repeat the same positionning without much error, wouldn't the OpAmp lower the signal to noise ratio?
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Not noticeably if the circuit is well designed. A good opamp circuit easily reaches 100dB or more of SNR.
    For A/D (and D/A) conversion the signal-to-noise ratio is given by SNR=6.02*N+1.76dB, therefore 100dB are equivalent to 116 bit accuracy of the DAC. Unless you are going to use a DAC with 18 bit resolution (and accuracy) upwards, a well designed opamp circuit is not the limiting factor when it comes to overall accuracy.
    Plus: a suitable opamp can deliver much more current than any precision DAC will give.

    Apart from these musings on the electronic side of your project: how precise is the mechanical side (actuator)?
     
  6. AnalogKid

    AnalogKid

    2,393
    665
    Jun 10, 2015
    Implied by Harold, you almost certainly will not be able to drive your positioner with the DAC output signal directly. Once a buffer is in there, throwing in a little DC offset is simple (the buffer has to have a DC reference anyway) and shouldn't introduce any significant, or even measurable noise of distortion.

    ak
     
  7. Chaotikmind

    Chaotikmind

    3
    0
    Jan 11, 2016
    Ok ok, then i'll go the op amp route i guess

    Tbh i don't know,
    but i suspect from what i gathered here and there, that in the original setup it was driven by a 20 bit DAC


    Btw i was completly unable to find any doc or schematics for that model, so it's not impossible i'll come back here to get some help , i'm not really good at electronics sadly.

    If someone has any info about the Ometron VPI V-9010-S scanning vibrometer, i take everything !
     
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