LabVIEW for photodiode

[Kim1997]

Hello everyone. My name is Sophia.

I am having a problem regarding the labview programming for my photodiode (Hamamatsu) by using DAQ.I want to create a programming from a software that is used for photodiode data value into the labview programming.

In this question, I put the picture of the software that has measurement interval, measurement count and time unit (ms,s, minute). I want that three things in my labview programming but I am stucked with this problem. I already studied the basic labview for three months but I am still stucked.

If anyone know how to do it, please guide me. Really appreciate the help.

[Kim1997]

This is the picture of the software.

[GerdW]

Hi Sophia,

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@Kim1997 wrote:

I am having a problem regarding the labview programming for my photodiode (Hamamatsu) by using DAQ.I want to create a programming from a software that is used for photodiode data value into the labview programming.

In this question, I put the picture of the software that has measurement interval, measurement count and time unit (ms,s, minute). I want that three things in my labview programming but I am stucked with this problem. I already studied the basic labview for three months but I am still stucked.

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So you have a problem: which one exactly?

(When you say "want to create a program" then this is not a problem, but a task…)

What about that picture? Do you already have a VI to do what you want to do?

Why don't you attach the VI instead of this frontpanel image?

Where are you stuck after 3 month?

Your task divides into several sub-tasks:

- let the user change some settings for the measurement

- start the measurement (including communication or DAQ with your "photodiode")

- display the measurement data in a table

- save the data (including sample count and timestamp) into a file

Which of these items have you already done? Again: where are you stuck?

[Kim1997]

Hello everyone. My name is Sophia.

I already done studying labview course but I encountered a problem regarding my photodiode signal detection.

I connect the photodiode to daq device and then I set the daq device for receiving signal using analog input for photodiode signal data records.

However, there is a problem for my data record using the waveform chart because it keeps receiving signal even though the photodiode do not detect any light.

Regarding this problem, I have three question:

1) Is there any wrong with the VI that I created?

2) Why the waveform chart still receive signal when the photodiode do not detect any light?

3) If it is related to the noise, how can I remove the noise?

In this message, I put my photodiode VI and the waveform chart result that I got. If anyone knows how to answer these questions, please feel free to help me.

[RavensFan]

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@Kim1997 wrote:

Hello everyone. My name is Sophia.

I already done studying labview course but I encountered a problem regarding my photo-diode signal detection.

I connect the photodiode to daq device and then I set the daq device for receiving signal using analog input for photo-diode signal data records.

However, there is a problem for my data record using the waveform chart because it keeps receiving signal even though the photo-diode do not detect any light.

Regarding this problem, I have three question:

1) Is there any wrong with the VI that I created?  Not necessarily.  It does what you programmed it to do.  The question is did you program it to do what you want it to do.

2) Why the waveform chart still receive signal when the photodiode do not detect any light?  Because it is programmed to receive 1 data point after every 50 milliseconds and send that to the chart.  I don't understand what you are expecting it to do differently.

3) If it is related to the noise, how can I remove the noise?  What makes you think there is noise?  I see are rather coarse chart with only 11 points that jump between -0.0008 and 0.0004.   Is that volts?  That is a very small number.  What numbers do you expect to see.  11 points at dt=50 ms means it is only 1/2 second.  How much change do you expect to see in such a short capture time?  a step of .0012 with a 5 V range means that jump is 1/4167 of your input range, remarkably close to 4096 which would be the resolution of a 12-bit DAQ device.  So I think you are reading 0V with slight noise on the level of 1 bit of the DAQ card, which is pretty much nothing.

In this message, I put my photo-diode VI and the waveform chart result that I got. If anyone knows how to answer these questions, please feel free to help me.

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Before you worry about the LabVIEW code, I think you need to worry about how you connected the photo-diode to the DAQ device and what kind of signal input you expect to see.

[cbutcher]

Hi Sophia,

1) The VI looks 'fine' - you might prefer to use DAQmx functions to improve readability, but this shouldn't significantly affect the function. Read this article if you want to know some basic steps: Learn 10 Functions in NI-DAQmx and Handle 80 Percent of Your Data Acquisition Applications 

2&3) Yes, this is probably "noise". You could check if the absolute value is less than some level, and set it to 0 in that case if you really don't want to see this, but like RavensFan said, it appears as though perhaps you have a wiring (physical, not LabVIEW) problem with your sensor. If it's really just black, try showing some light and see if it increases.

If the chart has an autoscale on both axes, and the length is very short, it might be that you're not seeing the change because the Y-axis rescales and you didn't notice the values, but perhaps that's a future problem 🙂

[Kim1997]

Ok I understood. I already repair the connection of photodiode to daq and get the result that I want. However, I still get some negative value on the waveform chart when the photodiode do not detect the light. May I know what is the reason?

[RavensFan]

Show your wiring diagram.  If the diode is turned off, it is a high impedance input.  It might be that the input channel will then float to either a positive or negative value.

[Kim1997]

Hi and thank you for your respond.

[a step of .0012 with a 5 V range means that jump is 1/4167 of your input range, remarkably close to 4096 which would be the resolution of a 12-bit DAQ device.  So I think you are reading 0V with slight noise on the level of 1 bit of the DAQ card, which is pretty much nothing.]

I kind of not understand about that statement. Can you explain it again?

I connected the photodiode to the analog input pin of the DAQDevice. So, I am expecting an analog input signal on my chart. But after the program is run, the signal seems like it not the photodiode signal. 

If I want the chart to display the signal between 0V to 5V in 60 seconds, what should I change in my VI?

and how to make the time display in the x axis of the waveform chart fix?

[RavensFan]

Do you understand how DAQ cards work?

If a card can can handle a range of 0 - 5V, and it has a 12-bit resolution,  that means it can measure 1 of any 2^12 values.  2^12= 4096.  So the smallest increment of voltage change it can measure is 5 V divided by 4096.   So a little bit of noise on your signal will "tickle" that last bit of resolution.  0.00122 volts.

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@Kim1997 wrote:

I connected the photodiode to the analog input pin of the DAQDevice. So, I am expecting an analog input signal on my chart. But after the program is run, the signal seems like it not the photodiode signal. 

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That is not the wiring diagram I asked for.  It is a written sentence that doesn't even truly describe how your photodiode is connected.  Which end is connected to the analog input pin?  Which end is connected to common?  Do you have any power supply or bias resistors in the circuit?

I can't see how you connected it, but my guess is that you don't have a valid circuit that will adequately measure the photodiode.