Photodiode for visible light

[Deepak Arora]

Hi

Couple of questions

1)

I want measure intensity of a LASER ( 633 nm) using a photodiode.For this I have a circuit with 5 v supply ( I get this from the PC using PCI 6013 card) where photodiode is in series with a resistance and I am measuring signal ( voltage) at the resistance.

Is there any other way of doing this ?

2)

PCI 6013 has only two pin outs for 5 v supply and I need to configure more than two photodiodes.I tried out drawing current for two circuits from a single pin out, but it did not work .

3)

I am using DAQ assistant to measure voltage and it has controls for sampling ( no. of samples and rate ) built in.

How can I have these controls on the front panel?

Thanks!

Deepak

[AnalogKid2DigitalMan]

Deepak:

1) That is one means, but you have to be careful about the range, that is the range of light intensity mapped to the range of voltage signal provided. A large change in intensity may only produce a small change in voltage. Here are some other photodiode circuits:

http://sales.hamamatsu.com/assets/applications/SSD/si_pd_circuit_examples.pdf

Personally, I prefer using a transimpedance amplifier- it has lower noise and faster response than just biasing the photodiode.

What is the make and model of your detector? Is the active area large enought so that you laser beam falls within it? Is the beam intensity too high which will result in saturation and nonlinearity of your signal?

2) It should have worked, as long as you don't exceed the 1 amp maximum current rating of the output.

3) Sorry, I have not used DAQ Assistant before, hopefully someone else will chime in.

Good luck!

[Dennis_Knutson]

The DAQ Assistant problem is simple. The assistant has inputs along the left side just like all of the other LabVIEW functions. These are the inputs rate, number of samples, etc. The names are visible whenever you move you mouse over them. You just have to create front panel controls and wire them to the inputs. The easy way to do this is to just right click on the input and select Create Control. This is an extremely basic task in LabVIEW. You should take a LabVIEW basics class or look into one of the many on-line tutorials.

[Deepak Arora]

Hello Anaogkid

Thanks a lot !

I will go to the link and will try different options,including the one you have suggested.

Area of the detector is large enough and I do get some noise but it's not significant . I,actually tr out different resistances and choose the one that gives me whole range (from zero to max intensity ) without any saturation.As you mentiooned,a huge change in intensity might result in smaller change in voltage.But as far as this change is consistant,I think I should be in a good position if I avoid the saturation and cove the whole range of intensities too.

Cheers

Deepak

[Deepak Arora]

Hello Dennis

Thanks!

But I do not see any controls for "clock setting"on the left side of DAQ assistant.Controls that I see with the DAQ assistant are -error in and time out (s) .

Cheers

Deepak

[Dennis_Knutson]

Then you are using the DAQ Assistant in 1 sample mode. When you check the properties of the assistant, are the clock settings greyed out? That means that they don't apply to the task you have defined. If you change the task timing to N Samples or Continuous, then the clock settings are not greyed out and the terminals will be available.

[Deepak Arora]

Hi Dennis

I am measurng signal n differential mode without any custom scaling.Input ranges from 5 v to -5 v and "acquisition mode" is "N samples" with internal clock type.But I do not see any controls for clock settings o the DAQ icon.

Also,what is the application of external cock ?Have you ever used it ?

Thanks!

Deepak

[Dennis_Knutson]

When you open the DAQ Assistant, you don't see this picture? If yours is different, attach a picture or the VI itself.

An exteranl clock source is just that. The source of the conversion clock can either be the internal clock on the DAQ board or something external like another data acquisition board.

Message Edited by Dennis Knutson on 03-23-200607:58 AM

[Deepak Arora]

Hi Dennis

I do see exactly the same .I just want to have the circled conrols at the front panel.

Thanks

Deepak

[Dennis_Knutson]

Then what exactly are you having trouble understanding. Like I said earlier, these are inputs to the function. Right click on the input and select Create>Control. If you want to do it the hard way, go to the front panel, drop a couple of numeric controls onto it, go back to the diagram and wire them to the assistant.