DLP NIRscan Nano EVM: Why exposure time does not affect spectrum's intensity

Ai Hong

When I acquire spectrum from DLP NIRscan Nano EVM, I change the exposure time like 0.6ms to 5.08ms, keep other parameter the same, the specturm's intensity did not change. As my knowledge, the intensity is proposal to exposure time (integrate time in other spectrometers).

Do I miss understand the expsoure time paramter?

Thanks.

over 2 years ago

0 Vivek Thakur over 2 years ago

TI__Mastermind 23070 points

Hello User,

Could you please upload the CSV file for both measures? This will help me under the system configuration.

regards,

Vivek

0 Ai Hong over 2 years ago in reply to Vivek Thakur

Prodigy 30 points

S_Gain1_Int0.635ms_Rep10_AHLocal_245041_20221021_093050.csv S_Gain1_Int5.08ms_Rep10_AHLocal_245126_20221021_095656.csv

Thank you.

0 Vivek Thakur over 2 years ago in reply to Ai Hong

TI__Mastermind 23070 points

Hello Ai,

Thank you for uploading scan data.

The DLP NIR Nano firmware takes multiple samples of detector output and averages them for the intensity value. When you increase the exposure time. It results in taking higher number samples but average remains same. The longer exposure time will result in better SNR, not increased intensity value.

You can use PGA gain to increase the intensity value if sample signal is not strong.

Hope this answers your question.

Regards,

Vivek

0 Ai Hong over 2 years ago in reply to Vivek Thakur

Prodigy 30 points

Dear Vivek,

From your description, When I set exposure time to 5.08ms, the device acquire 8 spectra with really inner exposure time 0.638ms. The finally spectrum output from device is the average from those 8 spectra.

At my knowledge, exposure time affect the intensity by the photo quantum count arrived at the detector, but PGA gain affect the intensity by amplify the electronic signal. These two increase the intensity with different way. When PGA gain amplify the signal, It also amplify the readout noise, dark noise and photo shoting noise.

If exposure time can affect inner acquire time, Why I need to set the parameter Num Repeats?

Thanks.

Ai Hong

0 Vivek Thakur over 2 years ago in reply to Ai Hong

TI__Mastermind 23070 points

Hello Ai,

Num Repeats averages over a complete scan whereas exposure time impact a measure at a wavelength level (very short duration). Averaging at scan level helps address variability due to system parameter like temperature, humidity, lamp warm up and any other low frequency noise.

regards,

Vivek

0 Ai Hong over 2 years ago in reply to Vivek Thakur

Prodigy 30 points

Hello Vivek,

1. Is the exposure time 0.635ms (fixed integrate time) actually for each wavelength?

2. Dose the scan level average happened when acqiure each wavelength, or on each spectrum?

3. What's the advantage to use this fixed integrate time method instead of variable integrate time?

Thanks

Ai Hong

0 Vivek Thakur over 2 years ago in reply to Ai Hong

TI__Mastermind 23070 points

Hello Ai,

I need to investigate into these subjects and will get back to you early next week with information.

regards,

Vivek

0 Akhil Guntumadugu over 2 years ago in reply to Ai Hong

TI__Expert 3825 points

Hello Ai,

Exposure time is the time for each frame of data displayed on DMD. These is not exactly for each wavelength.

The exposure time determines at what rate each pattern needs to get the data for that pattern. Note that these set of fixed timings, As the DMD has some in built sequences which allows only some fixed set of timings for patterns.

FYI for colum and Hadarmard scan exposure time is always 635usec. Only for slew scan configuration with more than one section, user can select from the other exposre times as well.

Regards,

Akhil

0 Ai Hong over 2 years ago in reply to Akhil Guntumadugu

Prodigy 30 points

Dear Akhil,

As you said, the exposure time can be difference between sections in slew scanning mode. so if I have two sections 900-1200 and 1400-1700, then I can set exposure time 0.635 x 2 for the first and 0.635 x 8 for the second eg.?

Regards.

Ai Hong

0 Austin Snyder over 2 years ago in reply to Ai Hong

TI__Genius 12785 points

Hello Ai,

We are looking into this and will reply by next week.

Regards,

Austin

+1 Akhil Guntumadugu over 2 years ago in reply to Ai Hong

TI__Expert 3825 points

Hello Ai,

Yes, You can set different exposure times for different sections.

Regards,

Akhil

0 Ai Hong over 2 years ago in reply to Akhil Guntumadugu

Prodigy 30 points

Hello Akhil,

I tested you advice with the GUI program, It can work now.

Thank you very much.

Ai Hong

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DLP NIRscan Nano EVM: Why exposure time does not affect spectrum's intensity