Update 19.03.2022

The deadline for sending our CanSat to the launch campaign is approaching, which is why we met again at the weekend to put the "final touches" to our probe. After the structure had to be reduced by a few millimetres and reprinted accordingly in order to comply with the required external dimensions of the CanSat, it was now time to finally place all the components inside in their finished state. However, before we also installed the pump system, we subjected the entire system to a final test in which we once again used the used and no longer sterile test bags. The following video shows the complete test using all the electronics installed on the launch day:

Sequence of the test:

0:00 When the power source is connected, the probe starts directly with the self-test programme of the electronics. In the finished state of the CanSat, this only happens after pressing the on/off switch, which is already permanently installed in the casing and was therefore not used for this test. The checking of the individual components one after the other is initiated by a long beep of the acoustic signal generator and returns the signal for "component functional" by a double beep.

1:07 Now the programme sequence for the case of the probe begins, which can be recognised by the humming sound of the pump. Actually, this part is only carried out after the launch and ejection of the probe from the rocket has been detected and the sensor system has been read out regularly in the meantime. For the test, however, we shortened this part and went directly to filling the gas collection bags in the programme sequence.

The filling of the gas collection bags starts with the first bag at the top left and then continues counterclockwise with bags two and three. Two factors are decisive for the filling time during which air is actively fed into the corresponding bag via pump and valves: the air pressure and the height calculated with it, as well as a maximum time interval that may not be exceeded. The former ensures that air samples from different layers are collected by the valves switching to the next bag at certain distances from the floor. The second stops the filling of the bag when the height intervals for filling a single bag are so long that continuous pumping into the bag could damage it if the internal pressure is too high. Since the ambient air pressure in the test setup is approximately constant, each bag is filled according to the second factor for just under 15 seconds. This is followed by a short venting of the system, during which all valves are switched to output. This is to minimise the mixing of gas samples from different heights by the air remaining in the hoses and valves between the filling of two gas collection bags. A short beep signals the switching to the next bag and the process repeats.

In the video it is difficult to see the filling of the gas collection bags. This is because we only take small air samples and the test bags used in the video are already very crumpled and not completely empty of air due to frequent use.

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