I'm using a 20mm LDR for my project measuring illuminance in lux but I'm not sure of its uncertainty. Would anyone know?
Measure the LDR multiple times across its diameter in multiple places using a micrometer. Then take the standard deviation. This will give you a measure of the uncertainty on the 20mm figure.
How about the uncertainty of its resistance or lux reading(after conversion from resistance)?
You need to look at the data sheet - usually there is a fairly wide tolerance with LDR light level and resistance .
Buy 10 from different sources and test them .
This site might help , note the max and min values in the data sheet
My coments about the diameter were really meant as a joke. I knew that is not what you meant to ask. But with so little of the important information about the ldr you are using, that was the only suggestion I could make.
If you want to measure lux, there are some much more accurate sensors available such as bh1750, which is what I use.
LDR's are temperature sensitive as well as light sensitive, for measurement you'd probably
be better off with a photo-diode or a light sensor chip (calibrated photo diode and amp in
one unit, often with digital interface).
How about the uncertainty of its resistance or lux reading(after conversion from resistance)?
It's called TOLERANCE, and is given in %. (ie, 20%,105,5%,1% etc.)
There's also RESOLUTION, ACCURACY
There is no spec called 'uncertainty'.
ASAIK
Thank you, everyone, for your replies. I'll be switching to a TSL2561 sensor. This is for one of my chemistry projects where I am measuring light emittance versus temperature. Uncertainty is a requirement in my course to know how precise the data will be.
Your question is a math problem. This topic is
General Electronics. As such, as I already said,
components DO NOT HAVE an 'UNCERTAINTY'
spec. They have specs like TOLERANCE,ACCURACY,
RESOLUTION, etc. It it up to you to look up these
specs, and DO THE MATH.
With multiple specs the complexity increases...
If you have a 5% resistor with a 10% temperature
tolerance you can see that you have to sum the
error of all the tolerances. It is 470 ohms at 25 degrees C or 100 degrees C ?
I've already gotten the uncertainty. According to my syllabus, it is just the smallest value that the digital sensor could read which is 0.1 for the TSL2561 sensor. I just was not sure with LDRs since it measures resistance which is then converted. It's a pretty grey area for me. Thanks though
it is just the smallest value that the digital sensor could read which is 0.1 for the TSL2561 sensor
As I said IT IS NOT CALLED UNCERTAINTY !
It's called RESOLUTION or ACCURACY
According to my syllabus, it is just the smallest value that the digital sensor could read which is 0.1 for the TSL2561 sensor
You will, or should, loose marks if you give that answer!
To calculate uncertainty, you must take many measurements in the same conditions and see how much the sensor readings fluctuate. Maybe it will be 0.1, but to get the marks you must show that you calculated the uncertainty by a proper method.
Is UNCERTAINTY a statistical term or a scientific term ?
Umm... yeah, one 'o them!
EDIT : Uncertainty
Also you should probably take many measurements in a variety of different conditions, to see if the uncertainty is the same across the range of the sensor.