Wednesday, September 30, 2015

LoRa under cover

This time we put LoRa underground, reading water meter 2 meters below the surface. Other technologies including cellular data and 2.4GHz had already proven to fail with this task. Let LoRa proof its capabilities.


Well located at parking lot.
It this test, a water meter is located in an infrastructure well located at parking lot. The well has heavy cast iron lid and also all-metal collar for depth of 25 cm. Walls of the well are made with concrete rings. The water meter is at the bottom of the well, approx. 2 meters in depth. 
Water meter at the bottom of the well.
We build a demo setup with Multitech Conduit LoRa gateway, and mDot integrated with Raspberry Pi and M-BUS master interface, all put in an IP-classified plastic box. The box is well over-sized, but there is good space for battery. The LoRa transmitter in the "shoe-box" is interfaced with the meter over wired M-BUS. RF transmit power is 14dBm and spreading factor 12.

LoRa transmitter and gateway.
The transmitter was located next to the meter at the bottom of the well. The LoRa gateway was located in a meeting room inside a nearby building. The line of sight between meeting room and the well was blocked by a storage wing covered by metal plates.



Building where the gateway was located.
Distance of the well and the building is approx 25 meters. For realistic condition, the lid was closed tightly and a van was parked above the well. In the direct line between transmitter and receiver, there is several meters of soil, metal cage, brick wall and concrete floor.
Diagram of the test setup
And the results? Excellent!

Received signal strength is approx. -105dBm, which gives wide margin left. The gateway could be located much further away. We also tested signal coverate inside the office building and got it all covered from the same gateway location, 100 meters through several steel reinforced concrete floors and brick walls.

What's the meaning of all this? In an automated meter reading application, whether water, electricity or other types of meters or sensors, even a large complex with outdoor environment and difficult locations like basements and underground locations, it all can be covered with a single gateway located pretty freely in most convenient location. Outdoor wall installation or other difficult to reach position is not necessary.

This time we didn't tested the maximum distance from the well where the signal can be detected, as the results were good enough for the purpose of the trial.

1 comment:

  1. Curious as to the path loss from the well and lid. Did you measure the sensor Received signal strength at the ground level? Was it 30-50 dB stronger? Thanks

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