BME280 Filter

Projects General Guidance
1

Hi everyone,
I’m building a project using an Arduino Pro mini and a BME280. So far everything works fine. My goal is the measure altitude every 50 millisecond as precisely as possible for a short among of time (5-10seconds). I found that the settings described in “Indoor navigation” (3.5.3 page 18) are great for my project.

There are however a few things I don’t understand even after reading the datasheet:
• What are “Filter bandwidth” and “Response time (75%)”? I guess it has something to do with the filter setting (p16), but I don’t understand what it means.
• What does “Samples to reach >75 % of step response” means? (p16)

Could someone please give some additional information? Thanks

BME280.pdf (1.85 MB)

2

RedIron:
Hi everyone,
I’m building a project using an Arduino Pro mini and a BME280. So far everything works fine. My goal is the measure altitude every 50 millisecond as precisely as possible for a short among of time (5-10seconds). I found that the settings described in “Indoor navigation” (3.5.3 page 18) are great for my project.

There are however a few things I don’t understand even after reading the datasheet:
• What are “Filter bandwidth” and “Response time (75%)”? I guess it has something to do with the filter setting (p16), but I don’t understand what it means.
• What does “Samples to reach >75 % of step response” means? (p16)

Could someone please give some additional information? Thanks

Step responce…. "Step responce" means that a significant change is made to the parameter being measured. Then the responce, the measurement, is done repeatedly until the reported value has reached 75% of the "correct" value . Some sensors needs time to settle at the correct, the best, value.

3

Thanks for your answer.
Do I get it right, so if I take (according to table 6 p16) the average of 22 consecutive measurements, I will reach 75% of the "correct" value?

I don’t understand the relationship between:
• Data output rate 25 Hz
• Filter bandwidth 0.53 Hz
• And response time 0.9s

My loop runs at 50 milliseconds (20Hz), I need that speed to capture sudden altitude changes (since I am building a rocket). According to my setting, the output rate is 25 Hz, which means that I can get at most 25 different measures per second right? Would that mean that even though I get a measure, it’s not the most accurate one since I'm not "waiting" those 0.9 seconds?

4 
•   What does "Samples to reach >75 % of step response" means? (p16)

Normally the "step" is applied to the sensor. Let's say a voltage jump from zero to +5V is made instantly. Then You measure the analog reading in high speed and check for the Reading to reach 75% of 5.0 volt = 3.75Volt.
I can't say what the mean by "Filtering". Averaging will increase the resolution on a stable signal and is rather useless during the "step face".

I downloaded the pdf. You can "average" to increase accurazy but the disadvantage is that it takes more time to get the final value.
As they tell, the humidity sensor is a slow reacting sensor beacuase it takes time for the surrounding air to get inte the sensor. They talk about slamming doors etc., changes in the surrounding air preasure, how that can effect the readings.

I assume that the air preasure reading will reach the correct value a lot faster than the humidity value.

Do some testing! Read the air preasure at the same time as You apply a "step" (put the sensor in a closed container and pump air into the container) and see what it looks like.

What is Your project? Measuring during a rocket launch?