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The Radiation Sensor

A project log for Portable environmental monitor

A handheld, battery powered, sensor array unit for environmental monitoring focused mostly on air quality using a global infrastructure.

Radu MotisanRadu Motisan 07/05/2015 at 19:060 Comments

One problematic issue was sourcing the proper detector, one that was both sensitive and small to fit the tiny space available in the already feature-crowded new uRADMonitor variant. After a slow process and intense communication with radiation detector manufacturers, we finally found a good candidate, putting price and performance in a reasonable balance: LND Inc and their excellent LND712 end window Mica Geiger tube.

uradmonitor_LND712_test_500V
To give it a quick test, the tube was hooked to one of the model A boards, and the voltage configured in software from 380V (which is used the SBM-20 and SI-29BG tubes) to 500V! Yes, the model A hardware supports that just fine with no other changes than a single constant changed in code, thanks to the excellent high voltage inverter circuit:
uradmonitor_inverter_target_voltage
uradmonitor_lnd712_voltage
The result was as expected, and can be seen in the second image. The voltage on tube measurement is presented, part of the internal inverter feedback mechanism, responsible for having a regulated output matching the target voltage, in this case exactly 500V.
uradmonitor_lnd712_geiger_4
Compared to the SBM-20, the LND712 shows the same sensitivity at a smaller size.
uradmonitor_lnd712_cpm
But the Alpha and beta radiation sensitivity is the plus we’re after , and we get that just fine thanks to the mica end window.
uradmonitor_lnd712_geiger_2
The BOM production cost, however, will inevitably increase, as a single LND712 gets close to $70, the tube only and this is just a little fraction of all the components that need to go in the new model D environmental dosimeter.

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