Position Sensing Detector Interfacing
Position Sensing Detector Interfacing
(OP)
I want to build the circuit attached with this post to measure the position of the laser.
Please clarify my doubts regarding it
1. What is the current range produced by each quadrant in the photo detector.
2. Can the gain of the transimpedance amplifiers and sum and difference affect the position information
3. Can the temperature effect the operation of the circuit.
4. The X and Y outputs obtained are in the form of voltage. How to read the position from them. Are they needed to processed further. If so then tell me what tools are needed to process them.
Thank You........
Please clarify my doubts regarding it
1. What is the current range produced by each quadrant in the photo detector.
2. Can the gain of the transimpedance amplifiers and sum and difference affect the position information
3. Can the temperature effect the operation of the circuit.
4. The X and Y outputs obtained are in the form of voltage. How to read the position from them. Are they needed to processed further. If so then tell me what tools are needed to process them.
Thank You........





RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
I want to use the 4 quadrant position sensing detector of Hamamatsu_s4349. I've pasted the link below which leads to the datasheet of the photo diode. I've known that each quadrant of the photo detector provides a current in the range of nA. I first want to build the pre-amplifier stage which must convert nA into mV and later sum and differential amplifier stage. Could you please suggest me regarding the selection of component values for biasing the op-amps.
http://www.hamamatsu.com/resources/pdf/ssd/s4349_k...
RE: Position Sensing Detector Interfacing
2. Yes, temperature can affect the measurement. Mainly temperature drift in the gain resistors, and then op-amp variation with temperature.
3. Yes. See #2.
4. A multichannel A/D converter is your best bet. You can get hardware that will plug into a PC for further processing.
Unless you have the time to learn a lot about electronics on this project, I suggest you purchase one of these:
http://www.thorlabs.com/newgrouppage9.cfm?objectgr...
Z
RE: Position Sensing Detector Interfacing
Mike Halloran
Pembroke Pines, FL, USA
RE: Position Sensing Detector Interfacing
I want to analyze the three outputs X,Y,SUM by using labVIEW. Can anyone suggest me a cost effective 3-channel data logger with PC connectivity for my project.
Vinay Kumar
RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
Thank you...
RE: Position Sensing Detector Interfacing
You have not mentioned your desired sampling rate or other critical items (voltage range, resolution, etc).
-AK2DM
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"It's the questions that drive us"
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RE: Position Sensing Detector Interfacing
You can't derive a laser spot position signal from the X,Y outputs of a quadrant detector. ... because there isn't a simple transfer function to infer where the centroid of the beam is, relative to the axes of the quadrature detector. The detector only indicates the direction in which the spot deviates from the detector center.
You have to _move_ the quadrant detector, physically, in two axes, to 'zero' the X and Y outputs of the quadrature detector and set up a servo loop to keep them zeroed. Then you can get X and Y position signals, from the motion system, not from the detector.
Alternatively, you can use the motion system to 'scan' the quadrant detector over the full extent of the beam, and use the detector SUM output and the motion system X,Y position signals to 'map' the beam.
OR, you could buy the Thorlabs Position Sensing Detector (not the Thorlabs Quadrant Detector) recommended by Zappedagain, which does have X and Y position outputs and shouldn't need to be physically moved unless your beam wanders quite a lot.
We're kind of guessing what exactly you're trying to do there.
Mike Halloran
Pembroke Pines, FL, USA
RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
Thank you.....
V
RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
Thank you...
V
RE: Position Sensing Detector Interfacing
Perhaps you were unaware of this, but laser beams tend to wobble with time. At least gas lasers do; I think it has to do with local depletion of active ions within the laser cavity, and I know that it's related to minute changes in the thermal environment of the laser tube and mechanical strains associated with thermal deflection of the tube's support. I assume that similar influences affect solid state and diode lasers. For gas lasers, the deviation is not great, a few milliradians or tens of milliradians, but it can make a huge difference in performance of the sort of applications where lasers are used.
Again, you need to state clearly, exactly what problem you are trying to solve.
Mike Halloran
Pembroke Pines, FL, USA
RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
V
RE: Position Sensing Detector Interfacing
Your proposed circuit plus LabView allows you to plot 'voltage'.
You have not mentioned how you are going to control the laser beam position or how you are going to measure random position changes, so you don't have a way to plot 'deflection'.
Mike Halloran
Pembroke Pines, FL, USA
RE: Position Sensing Detector Interfacing
However, I reiterate, a quad detector is just not that accurate for position MEASUREMENT; it's really for position SENSING, i.e., it will tell you roughly where the spot is. Additionally, most laser beams tend to be very small, and therefore produces large amounts of position noise on a quad, particularly if the beam is straddling two quadrants. You are better off with either a quadrilateral device, which has no gaps, or just a camera, which has much higher precision and resolution.
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RE: Position Sensing Detector Interfacing
IRstuff, I think understood why the quad detector can only be used for sensing the spot of the laser beam. Can you explain me what did you mean by position measuring.
Can data loggers continuously record and store the information. What does the sampling rate of a data logger mean.
RE: Position Sensing Detector Interfacing
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RE: Position Sensing Detector Interfacing
I suggest that you assign yourself this homework.
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RE: Position Sensing Detector Interfacing
RE: Position Sensing Detector Interfacing
Forget the datalogger and LabView for now.
Don't spend any more big money. Rig up whatever hardware you've got already and try to read the X,Y outputs of your quadrant detector preamp on a couple of cheap multimeters. (the kind you get on sale for $3 at Harbor Freight, so you don't care if the smoke comes out)
Then tell us what you find out.
Mike Halloran
Pembroke Pines, FL, USA
RE: Position Sensing Detector Interfacing
I detect that you are a human, but can't quantify where you live, particularly since you apparently can't access Wikipedia or Google.
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RE: Position Sensing Detector Interfacing
Thank you for your time....