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Appropriate DAC

Chaotikmind

Jan 11, 2016
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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?
 

Harald Kapp

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Nov 17, 2011
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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)
 

Chaotikmind

Jan 11, 2016
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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?
 

Harald Kapp

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wouldn't the OpAmp lower the signal to noise ratio?
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)?
 

AnalogKid

Jun 10, 2015
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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
 

Chaotikmind

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

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