VL53L1X calibration with cover glass

[SWand.1]

Hello everyone,

I am currently trying to calibrate VL53L1X sensors which are covered by a 4mm thick glass.

I am using the ULD from ST to calibrate the offset and xtalk.

I achieve a better result with calibration, but I still don't get further than 70-80 cm.

According to the user guide the ranging curve with calibration should look like this.

But in my case it looks more like this:

So basically just like the ranging curve without xtalk calibration, only now the deviation starts a little further away.

In the calibration process I also noticed that the XTalk calibration distance (XCD) determines the achievable range of a sensor after calibration.

For example, if the XCD of a uncalibrated sensor is at 85cm, the range to which the sensor can produce acceptable results after calibration is also around 85cm.

But the above picture found in various user guides shows that after calibration the sensors should also produce good results for ranges bigger than XCD.

Am I doing something wrong? Is it the cover glass?

We are aiming to range up to 100cm, currently we only get acceptable results to about 75cm.

My configuration:

Distance-Mode: Long

Timing-Budget: 100ms

For the calibration process, I follow the instructions given in the ULD user guide.

[John E KVAM]

You did great. You did everything except choose a good coverglass.

My guess is that the glass is not very transparent. And a 4mm thick glass is pretty darn thick.

Best way to tell is to range on some different things.

A white sheet of printer paper is 88% reflective. Put 4 of them on a piece of card board and see how far you can range.

Then flip the cardboard over. Normal cardboard is about 50% reflective. See how far that gets you.

If you find the white works better, it's because not enough photons are escaping your glass.

But cardboard and people are about the same reflectivity, by the way.

Read the article at the top of the Proximity Sensors page.

It will tell you how to choose a better coverglass.

Coverglass

• john

[PRuiz.1]

Hi,

I have a similar problem with the VL53L0x but the coverglas that I'm using is 1mm, like this:

 

When I calibrate the sensor I have two problem, depends of calibration:

1) I get a overrange measurement (8191mm)

2) I get a good measurement in 470 mm +- 100mm but when I try to measure distance >570mm I lose this measurement I get 150mm o 200mm again (in a dark environment) If I measure outdoors I get a aproximately measure.

What can be my problem?

[John E KVAM · Accepted solution]

that Hornix glass is pretty good. They designed it with our help. And apparently they sell quite a number of them.

I would have thought you could contact Hornix and they would give you a Crosstalk value.

But lets look at your issues.

1) an 8191 is NOT a measurement. It's the number you get when the RangeStatus indicates that the range failed. It's generally 8192 minus the Range Status. So you got RangeStatus=1.

Look the Errors up in the user manual.

If you are using the VL53L0X the error would be:

1 - Sigma Fail - "Sigma fail will trigger particularly in ambient light, when the amount of ambient light is adding too much noise onto the ranging measurement."

If you "lose the measurement", the object you are ranging on is either too small or too dull to get a measurement. Again, look at the Range Status to see what's going on.

When we say the sensor can range to 2M, that best case. A nice large reasonably reflective surface. Like a wall. The sensor will generally detect people to 1.5M as people are relatively large. You can spot hands to about 70cm.

• john