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Controlling Light Source

Hello there

I am trying to test image sensors but I am finding it really hard to change the intensity of the light source that I have. I was wandering if you guys have ever heard of, or maybe used a light source that can be controlled with LabVIEW. (a light source can be anything that illuminates a certain scene or area) Ideally, I would want to system to be totally automated and I was to have the ability to control everything I am using in this system with LabVIEW.
I was thinking of using an NI analog board to output different voltages to control the light intensity, but that is not the best and most reliable way to do this.

Any help or ideas would be greatly appreciated.
Thanks
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Message 1 of 12
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If you want reliable measurements, I would look at dedicated calibrated light sources. Intensity-calibrated light sources are really quite expensive though.

Another choice would be to include a radiometer (light intensity measuring instrument) in your measurement setup so that you always have an accurate "is" state of your illumination. Once this is done, you can program LabVIEW so that your intensity is changed until the radiometer says X. In this way, the radiometer is the defining step, not the analog output of the NI board (If this will even work directly).

What light sources are you thinking of using?

Hope this helps

Shane.
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)
Message 2 of 12
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Hello
I am aware that the calibrated light sources are quite expensive. I wish I could find a calibrated source that can be supported by LabVIEW. Currently, I have a monochrometer from Acton Research and I can control the monochromoter using labview, but NOT the light source. Changing the light source is still manual.

I am not sure what a radiometer is. I will look it up.

If I am desperate, I will just connect a DC light source (possibly and LED bulb or something of the sort) and simply change the voltage supplied to it from a DAC on an NI board. These are all tentative ideas. Ultimately, I would need a good calibrated light source, and my life as a test engineer would be 1000 times easier if I could control it with LabVIEW.

Thanks again,
Rami
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Message 3 of 12
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Hi Rami,

the problem is simply that an LED doesn't offer intensity stabilised output, even if the supply voltage remains constant. This is why the calibrated intensity sources are so expensive, they're guaranteed to vary by max 5% (Yes, so much) over time. A 5% difference in light source intensity is actually quite low, some sources display FAR more than that.

This is why I would recommend some kind of light-measuring feedback in your measurements. Maybe a stable photodiode or something similar will do, just so that you can actually "know" what your LED is delivering at any given time. Otherwise, you've really got no control over the current intensity.

On another note, does your monochromator have controllable entrance and exit slits? If so, these can also be used to control the intensity, but coupling these into a fibre may change the NA of your light source.

How much effort you need to put into your set-up really depends on how thoroughly you need to characterise your sensors.

Hope this helps

Shane.
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)
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I control 2 different light sources with Labview. The first is an LED ringlight. It is made by Advanced Illumination, and the power controller has an RS-232 interface. Power can be set from 0-100%. Let me know if you need the VIs to run this. The second is a Fiber Optic Light Source. It is a Shott-Fostec DCR-III. The intensity is controlled by a 0-5VDC signal. I use a camera for feedback, as open loop settings are not always repeatable. I also have an illumination meter that has an analog output. The model is DX-200, although I never used it with the analog output.
Message 5 of 12
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Hello Brian,

Thank you for your suggestions. I think this might be exactly what I am looking for, minus the calibration part, hahaha.

I am very interested in the Advanced Illumination option. Can you give me more info about it. What Model is it? And how much light does it produce in lux or visually?
I am putting my sensors in a closed, light sealed place, and I would like my light source to be able to adequately illuminate the scene. I would also like to have the VI you use, or a stripped down version of it.

Thank you very much. I appreciate your help,

Rami
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Message 6 of 12
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Hello Shane,

I see your point about the calibration and the source variation with time. I guess a "quick and dirty" solution would suffice for me for the time being, but eventually, I want to move to a more sophisticated and reliable system which I'm sure will have to include some sort of feedback.

THe monochrometer I have has an input and an output slit. I can use these to calibrate the light intensity. However, the amount of light "outputed" by the monochromoeter is ridiculously low. I know however that that output is highly calibrated and very stable (hence the huge $$ we paid for it). So I am just using the White light source that feeds the monochrometer since it provides so much more light, but controlling how much light is outputed is a pain because this light source has a manual dial to adjust the light.

Do you know of any expensive, calibrated light sources with PC interface?
Thanks again for your help and time,

Regards,
Rami
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Message 7 of 12
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Rami-

I don't have them in front of me, but the Edmund Optics part# for the controller is G55-900. It works with a variety of different LED illuminators. Check out the website or a catalog to find the ones you need.
Message 8 of 12
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I think the Schott-Fostec DCR units also have an RS-232 option to control intensity instead of a 0-5V signal (saves cost of a DQ card, forget what the RS232 option costs though)
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Message 9 of 12
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Brian,

 

I have a light source that is comprised of a power supply and an optics head with a thermally stabilized monitoring detector.  I've taken a LabVIEW course (and should probably retake it).  I do have the .NET dll for the instrument.  I would be incredibly grateful to see the VI that you put together, if only to see the architecture that you used.  I imagine it would include event structures, but just getting started is giving me trouble.  

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