VL53L4CD - Calibration Procedure and Tools

[GCout.1]

Hello,

I'm working with VL53L4CD to have the distance between the board and some liquid. This distance could go from 20mm to 250mm. 

We want to protect the board with a glass and then do a calibration, first Offset then Crosstalk. Into the user manual, I found that I need to do the offset calibration on a 17% reflective target at 100 mm and the crosstalk calibration on 17% reflective target at maximum ranging distance without under-ranging. 

My questions are : 
- Do we really need a 17% reflective material as target ?
- 100mm is mandatory for the offset calibration ?
- As our system goes from 20 to 250mm, is it possible to perform the Crosstalk calibration or do we need to take the board outside of our machine to be at the right distance ?

Thank you for your help,
Kind regards,

[Zhiyuan.Han]

Hi 

Thanks for sharing your use case,

For offset calibration, the value from user manual is the generic approach to get best accuracy. you can try a different combination, make sure the calibration distance is not too long, and you need to evaluate the accuracy meets your use case requirement. 

For the xtalk calibration, normally 250mm is too short, so we suggest you take the module out from machine to the right distance.

And at last, I suggest you can have a look at the liquid level monitoring user manual to fine tune your system. 

Water and liquid level monitoring using VL53L4CD Time-of-Flight high accuracy proximity sensor - Application note (st.com)

Br

Zhiyuan.Han

[GCout.1]

Hello,

Thank you for the answer.
Concerning the reflective material, the 17% is mandatory ? Do you have material, paper color that correspond to this ?

Kind regards,

[John E KVAM · Accepted solution]

That 17% is NOT mandatory. Any reflectivity target will work. The darker target, the closer (and smaller) your target can be. Just find a reflectivity and a distance were you are under-ranging by 10 or 20% and then do the calibration, putting the known distance into the function call.
If you choose to paint your own target, use a flat (matte finish) paint, and use several coats to get really good coverage. If you have a good cover glass with low crosstalk, you might get away with using a black. With a less-optimal coverglass you might need a dark gray. And a light gray should always work.
When you find a system that works, Keep the can of paint in case you need another target. Paint cans are NOT guaranteed to be consistent from one can to another.