I need to connect more than 80 energy meters using modbus interface with weintek hmi. My concern is that can it handle all meters directly using rs 485 com port or do i need to make segments of 32 meters… Need help 2nd option is to connect them with wincc scada… What are the requirements for this ?
It can handle. But I recommend that you should use 2 or 3 rs422/485 signal repeater in your network in order to avoid fluctuations.
I suggest you use a gateway (RS-485 <> Ethernet) … divide the meters over 2 or 3 gateways, then you can read all of them from the HMI. Also, you can connect all the meters to one plc, let all their readings sorted sequentially in the plc memory, then connect the HMI to one plc and read all memory addresses in 1 read cycle.
You must definitely have a look at the Vbase. I would’ve done this in WinCC using faceplates. Also, I would segregate the meters into three groups 25, 25, and 30, leaving some headroom per group of course
The EIA standard is a maximum of 32 nodes, but a repeater can extend the network to beyond 32 nodes.
One consideration is how daisy chained wiring will work out in reality, sometimes it’s necessary to go to multiple serial ports with fewer nodes because the layout just does not support daisy chained wiring.
The other consideration is the Modbus protocol which being a master/slave protocol the master polls, waits for a reply then polls the next device in sequence. Three networks of 25, 25 and 40 nodes each increases the ‘throughput’ time by three; any given node is polled/sampled in 3 times more often that a single network of 80 nodes using repeaters.
A failed node will delay all subsequent responses as the master waits for a reply that is not going come. Your master should have a relatively easy means of removing a node from the polling sequence for the inevitable shutdown/failure/turn-around when one or nodes are not available.
With that many electrical meters, the environment is likely electrically noisy, so cabling should be premium cable, shielded twisted tri-conductor (3 conductors) because RS-485 is a differential signal, the difference of the voltage of the A driver line referenced to signal ground and the B driver line referenced to signal ground. Without a local signal ground reference of the 3rd wire, you will run into problems on a big multidrop network. Don’t let signal cable run in power cable conduit or trays. Don’t use cable spurs or Tees to connect to a node.
The master should bias’ the driver lines with pull-up/pull-down resistors.
Do a web search for “AN-1056, Ten ways to bulletproof RS-485”, a Texas Instruments app note, the people who manufacture the RS-485 chips.