Length of the tube > 20 CM?

1

Hi all!

In the data sheet I read that the length of the tube should not exceed 1 meter.
The instructions say to use a tube of 20 cm.

My question is: does it make a difference? Has it been tested? I’d like to use 40 cm of tube to keep the electronics inside the house and still get air from outside through the wall. Is that still ok?

Thanks,
Rutger

2

Hello,
with a longer tube there will be less air per time flowing through the sensor.
Someone tested this and got the following values for the air flow:

tube length (cm) air flow (ml/min)
100 412
80 462
60 526
40 601
20 664

So you will have around 10 percent less air flow. And with that lower PM values.

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3

thanks ricki. many builds lack a hose. our design uses a 5cm long hose and a separate inlet filter chamber.

btw- if the wall on the hose is too thick, it won’t go over the barbed fitting.

i read in the spec to avoid direct light because it could interfere with the laser optics. black hose reduces glare.

one advantage of the sds over pms is the separation of the inlet from the fan discharge by virtue of a black hose. another advantage is a larger laser chamber that won’t gum up as fast.

those flow calculations are helpful.

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