Quote:
Originally posted by bigben2k
Using a VCO (Voltage Control Oscillator, PDF, 24 pages, see page 1), is half the circuit.
Now to convert the input voltage to ^2...
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You are starting out on the wrong end. Forget about the VCO.
You should be looking at sensors at this point. There's no reason to think that the one I linked is anywhere close to the best choice. There's definitely not enough technical data on that Omega web page. (Omega doesn't want you to know how to use the sensor itself. They want you to buy a box to hook up to it.)
What accuracy are you going for?
How closely do you think your heatercore will match one that Bill has tested? Or, do you plan to calibrate it / have it calibrated?
How much of your error budget will be eaten up by the uncertainty of the heatercore calibration?
How much by the dp sensor? How much by the amplifier? Etc...
Things to look for in sensors:
Full scale that is only slightly above the maximum dp you expect to apply.
Availability of detailed specs and ideally applications notes.
Relatively high output voltage. The higher the sensor output voltage, the lower the signal to noise ratio coming out of your amplifier stage. Sensors with preamps built in are available and can save on additional circuitry. Extra cost for a sensor that has an internal reference and already amplified output is probably money well spent.
Good accuracy at an excitation voltage around 7V. (Because I can send you an LM399 voltage reference which has an output around 7V. We cherry pick them to tighter tolerance than the manufacturer, so we've got a thousand or so 'dropouts'.) Maintaining 10V +/- 5mV is not that easy. The LM399 is overkill though.
I'm sure there are other things that I haven't mentioned, but it's definitely worth searching through what's out there with these issues in mind.
WRT "square rooter":
http://www.analog.com/UploadedFiles/...471AD532_c.pdf