The ultimate right way around the loopy grounds problem is ground isolation - either at the PSU, or within the device, perhaps preferably at the RS485 port - so that the RS485 bus can have its own reference ground, yet the case of every device can be bolted down to the mains protective earth. Earth isolation is expensive, may require purchasing of additional isolated PSU's (where you already have a grounded PSU from the vendor), or purchasing of addon isolated bus transceivers (when you already have a non-isolated port on your device, chosen for other reasons). The fastest RS-485 transceivers out there right now are running about 50 megabits. It also means that the transmission loses some of its "attenuation budget", because the signal amplitude gets closer to the receivers' nominal voltage sensitivity (the signal gets attenuated right at the driver's output). A binary 1 may (or may not) be inverted by the driver before it is output. Anyway - nodes with a properly isolated RS485 port can be attached to the shield ground directly, without this 100Ω resistor, and such direct ground connection may prevent some common-mode wobbling of the pair against the shield. How fast can you go?

Modern processors are fast enough that handshaking is rarely needed. The usual transfer rates are just so low, that bit length is several times (orders of magnitude, rather) greater than the transmission-line round-trip. Besides, the UARTs usually sample the input waveform somewhere halfway though the bit duration - thus, RS485 standard some fuzz about the edges doesn't matter much. So I let the SCADA software crank away, to show me some traffic, and tweaked the scope a bit - looked at the fuzz around bit edges, possible interference, differential mode, common mode. Common-mode noise (reference ground wobbling) is often tolerated as well, at even surprising levels (you never get to know, until you plug in a scope). So, after some cabling exercises in the lab, I decided to pay a visit to the customer, to see with my own scope exactly what was going on. This is (almost) no problem as long as the power is distributed along with the bus signals (note that it's inappropriate for other reasons to daisy-chain power distribution cabling just like the RS485 signals). R1401 is a pull-up resistor that keeps the motor turned off during power up. In the built-in fail-safe input bias method, (explained in the previous section) extra circuitry incorporates large pull-up and pull-down resistors on the receiver inputs.

Devices with a properly galv.isolated RS485 port (isolated from PSU input) theoretically don't need a reference ground, and can work with the bus using just some weak internal biasing resistors. Last but not least there is also the GSM version which is useful especially if in the place where we are there is only one temperature to transmit to the server (calling a GET/POST script on your server; Web server which can also be the "internal" ControlHUB server, which already has the script to receive the data automatically). The maximum data transfer rate of RS485 is 10 Mbps over a distance of up to 1200 meters. The baud rate essentially means DC to the cabling. The one thing that's amazing about RS485, is its great tolerance to the cabling used. The Electronics Industry Association (EIA) has produced standards for RS485, RS422, RS232, and RS423 that deal with data communications. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. How does RS-485 handle bus fault conditions? 200 oC), flame retardant, resistant to most organic solvents, oil, as well as aggressive inorganic chemicals, resistant to UV, ozone and weather conditions in general, mold-resistant, mechanically resistant against wear, creep, cracking under stress - owing to both the insulation material and the fine conductor stranding.

Well if you paid attention to the previous discussion, there is no way. I have tried Raspberry Pi 3 as well as BananaPi. In other types of communication gadgets, say a 232-to-485 converter, both the local (232) part and the long-reach (485) part may have to be powered somehow, usually by a miniature monolithic DC-DC converter. The local 232 port will likely remain un-isolated from the converter's MCU, if there is any. That way, the local data inteface (232 or 485) ends up being directly connected to the "brain" of the modem - the processor chip(s). It is known for being able to be used effectively over long distances and in electrically noisy environments. For RS485, the impedance of just 70 Ω may prove a tad too low for longer distances. There are however lower-grade "fire-resistant" cables matching the general "shielded twisted pair" specification, for basic signaling applications, which can also be used for RS485 for shorter distances. The meter can be hooked up directly to a computer via standard Modbus RS485. Most Modbus implementations use RS485 due to the allowance of longer distances, higher speeds and multiple devices on a single network.