RS-485 interface for water meters
This week we tested a new RS-485 board to be used for wiring water meters for apartments. This is in addition to the wireless water meter solution we developed last year using the WSN1120L wireless mesh nodes.
In apartment complexes, water meters are usually one below the other in one or more plumbing/utility shafts. Wiring meters using a multi-drop bus such as RS-485 is a more cost effective and reliable solution in this case.
In India, it is common for apartment complexes to have multiple water supply entry points for each apartment. This means we need multiple water meters for each apartment. These entry points are usually not close to each other. Multiple RS-485 strings are therefore required to connect all these meters. All this adds to the cost of the overall solution.
We have so far tested 1 master RS-485 node and 2 slave RS-485 nodes. Each master node can collect metering data from up to 31 slave nodes. A slave node can accommodate two water meters. The master node will have a wireless interface (WiSense Sub-GHz radio or GSM/GPRS module) for cloud connectivity. Even if there are multiple RS-485 strings, only one master node needs to have GSM/GPRS connectivity. All the other master nodes will connect to this one over the WiSense Sub-GHz radio network. Broadband internet connection (if available) can be used instead of GSM/GPRS.
Here are a few pictures of our initial test setup. You can see the master connected to a slave through 50 feet of shielded twisted pair CAT-5E cable.
Here is a closer look at our RS-485 interface board. Each board has a micro-controller, an RS-485 transceiver providing half-duplex communication and a 5 bit dip switch for assigning address (1 to 31) with 0 reserved for each string’s master node. All the nodes are daisy chained. Power is supplied through the master node over the CAT-5E cable.
Here is a pic of a water meter connected to a slave board.
For more information, please visit wisense.in.