Is there any kind of ADC with +/-15V input voltage? Thanks!!!

[supercc]

Hello, I'm a freshman to use labview to make a quadrant photo diode sensor with a pre-amplified circuit. However, I found the power supply for op amps is +/-15V, and my current DAQ system is USB 6009 which only allows -10 V to 10 V. I expect my signals(X=(A+B)-(C+D),Y=(A+D)-(B+C)) can be as large as -/+ 15V. So I was wondering if there is such a ADC for labview with a high input voltage to satisfy my experiment. Thank you very much!!! 

[johnsold]

There are DAQ devices with higher input ratings. But it sounds like you are a student learning to design circuits and measure the results with the DAC system.

I suggest that you design a simple clamp circuit which limits the voltages to the 10 V range of the USB-6009.  Adjust the gain on the X and Y signal conditioning circuits (the pre-amplifier) so that the nominal maximum operating voltage is just less than 10 V.  With a quadrant photodiode circuit you will be more interested in relative values than absolute values so 10 V or 15 V really does not matter much.

Next year, when you are ready for a bigger challenge, make it work when the signal from the laser is smaller than the ambient light.  I designed a system similar to that about 30 years ago for a commercial application.

Lynn

[supercc]

Hi Lynn,

Thanks a lot!! Actually now I'm doing a project to use this sensor to detect a tiny displacement(maybe several hundreds microns) of a laser spot. So I need a larger detecting range from my sensor. what's more, I made a power supply which converted AC to DC and it only can output +/-15V. So that's why I need a DAQ device with a higher input.

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@johnsold wrote:

There are DAQ devices with higher input ratings. But it sounds like you are a student learning to design circuits and measure the results with the DAC system.

I suggest that you design a simple clamp circuit which limits the voltages to the 10 V range of the USB-6009.  Adjust the gain on the X and Y signal conditioning circuits (the pre-amplifier) so that the nominal maximum operating voltage is just less than 10 V.  With a quadrant photodiode circuit you will be more interested in relative values than absolute values so 10 V or 15 V really does not matter much.

Next year, when you are ready for a bigger challenge, make it work when the signal from the laser is smaller than the ambient light.  I designed a system similar to that about 30 years ago for a commercial application.

Lynn

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[johnsold]

You can make a clamp circuit work with the +/-15 V supply. Two diodes and a low impedance voltage divider can make a simple clamp.

How wide are the dead spaces between quadrants? How big is the spot?  How noisy is the laser? How much vibration do you have?

Lynn

[supercc]

Oh I see the point to the power supply. The gap distance is 50 micron and the area of each segment is 1.44mm^2. So I adjusted my laser spot diameter as around 1mm to get the largest linear range. The noise of laser is around 0.05V. And the vibration of the laser spot in my experiment is pretty slow(below 10 Hz).

BTW, since the sum signal is very large and X and Y are almost zero at start, I was wondering if I could use one DAQ device to generate two separate charts to have a better look to X Y changes.(one contains X and Y while the other contains the sum signal.) Thank you!!!