How susceptible is the the VL53L1 sensor to condensation forming on the cover lens? Many thanks!

[John E KVAM · Accepted solution]

Water is somewhat tranparent. But not entirely.

The light coming reflecting off the coverglass and returning immediately is called Crosstalk. Normally Crosstalk is calibrated out and it's not much of an issue. But in your case the water is going to increase the crosstalk and thus cause the sensor to under-range.

How much it under ranges depends on how much water builds up on the glass.

One can artifically increase the crosstalk compensation, and over-range in no-water situations, assuming that when some water hits the range will be perfect and with too much water you under-range slightly. (This is all a trade-off.)

There is 'smudge' correction on the VL53L1CB chip, but in order to use it, at least some of you ranges must be without at target in the first 80 cm or so.

With the VL53L1X the under ranging gets worse with distance.

With the VL53L1CB, the under-ranging is an issue as well. But at 80cm the under-ranging issue simply goes away.

• john

[AGome.7]

Are the sensors capable of detecting the condensation on the cover glass? In our application the lens cover COULD become full of condensation during normal operation. In that condition we would like to know whether our distance measurements are valid or not. How can we relate the sensor's ranging measurement to a foggy lens condition?

[ACHOU.18]

Hi, 

We experienced that condensation on the cover glass significantly reduces the ranging performance (under ranging) due to blocked laser emission and return signal. In cases where condensation is a regular occurrence, eliminating it might be challenging. However, if the device experiences occasional steam exposure followed by drying periods, then you get under ranging and as soon as drying and enough signal returns then you get normal ranging. 

[AGome.7]

When the sensor experiences steam exposure, and the sensor experiences under ranging, will the sensor output an error code related to the under ranging?

[ACHOU.18]

If I remember correctly, there is no error code. you can see the quite significant under ranging value. 

[John E KVAM]

Have a look at the Hornix cover glass. www.hornix.com.tw - click on the products page and scroll to the bottom. The 'no crosstalk covers' use two bits of window separated by an opaque barrier. Using this you will completely remove any crosstalk error. No photons can get from the TX side to the RX side with hitting your target.

You can buy the glass form hornix or you can build your own. But the opaque barrier has to prevent the light from leaking. Hornix built that 'glass' to my specification, but they are an entrirely separate company. 

That will fix your issue.

- john