OPT3002: Different sensor values in conversion mode Single-shot and Continuous

Ulrich Pahl1

Part Number: OPT3002
Other Parts Discussed in Thread: MSP430FR5728

Hello,

we have an application were we use the OPT3002 sensor to measure the irradiance of LEDs.
The OPT3002 is connected to a MSP430FR5728. The OPT3002 is configured as follows:

End of Conversion mode
Automatic Full-scale setting mode

and we have varied the following settings:

Conversion mode:
1. Single Shot mode
2. Continuous mode
Conversion time:
1. 100 ms
2. 800 ms

The following figures show the differences in the sensor value depending on these variations.

Measurement conditions:

The LED is driven by constant current source.
We have measured the irradiance at the following LED currents: 50 mA, 100 mA, 200 mA, 300mA and 500 mA.
The measuremnt is done more than 10 times with an reproducibility of +/- 5%.
The value of the irradiance is given in digits.

Diagram 1: Irradiance measured in single shot mode - conversion time: 100 ms and 800 ms

Diagram 2: Irradiance measured in continuous mode - conversion time: 100 ms and 800 ms

The sensor value measured in continuous mode at LED currents of 50 mA and 100 mA is about twice the sensor value measured in single shot mode.
At LED currents above 100 mA both conversion mode deliver nearly the same sensor value.

So we are wondering about these strange results and we are looking for an explanation.

Best regards

Ulrich

over 5 years ago

0 Ulrich Pahl1 over 5 years ago

Prodigy 190 points

Hello,

here are the diagrams.

Diagram 1:

Diagram 1

Diagram 2:

diagram 2

0 Alex Bhandari-Young over 5 years ago in reply to Ulrich Pahl1

TI__Mastermind 25845 points

Hi Ulrich,

I am not able to see the diagrams in either post. Did you use the "insert/edit media" button when adding the pictures?

Best,

Alex

0 Ulrich Pahl1 over 5 years ago in reply to Alex Bhandari-Young

Prodigy 190 points

Hi Alex,

excuse my fault, but here are the diagrams.

Diagram 1

Diagram 2

Regards

Ulrich

0 Ulrich Pahl1 over 5 years ago in reply to Ulrich Pahl1

Prodigy 190 points

Hi Alex,

Do you have any idea concerning the described topic?

Best regards

Ulrich

0 Alex Bhandari-Young over 5 years ago in reply to Ulrich Pahl1

TI__Mastermind 25845 points

Hi Ulrich,

This behavior is not expected. I know you said you have done the experiment multiple times to confirm that variation in the light source is not an issue, correct? Such as thermal stability. I will check the data we have to specifically compare single shot vs continuous mode to double check as well.

Best,

Alex

0 Ulrich Pahl1 over 5 years ago in reply to Alex Bhandari-Young

Prodigy 190 points

Hi Alex,

I think thermal stability is not an issue in this case. The temperature was stable (+/- 1°C) during the whole time of the measurements.
Maybe measuring very small irradiance values could be an issue. If you have a look into the diagrams, the issue occurs at irradiance values below 6000 digits.

Best regards,

Ulrich

0 Alex Bhandari-Young over 5 years ago in reply to Ulrich Pahl1

TI__Mastermind 25845 points

Hi Ulrich,

While I am checking on my end, do you have a reference meter to use to compare against the OPT3002 reading? Best would be if we can compare the reference power reading with the OPT3002 reading so we can see the error. LED current may not be linear with LED output optical power.

Best,

Alex

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OPT3002: Different sensor values in conversion mode Single-shot and Continuous