RS-485 was created in 1998 and is frequently used in
industrial and automation spaces. RS-485 is a standard that defines the
electrical characteristics of the drivers and receivers for the communication
protocol. It is transmitted over two signal lines, A
and B, which must be balanced and differential. Balanced signals are two lines
sharing a pair in a twisted pair cable with the same impedance along each line,
and matched impedance at the receiver and transmitter. Using a twisted
pair cable provides noise immunity. Because RS-485 is a balanced
transmission standard, there are two pins for each transmission and each
reception – a positive and a negative.
The main benefits of RS-485 can be seen below:
- RS-485 is regularly used with mission-critical
applications due to its reliability. RS-485 is a hard-wearing protocol, so can
withstand harsh environments.
- It is easy to scale RS-485 to support more
devices or a higher data throughput as requirements change. RS-485 is a
flexible communication protocol and is easily adapted.
- RS-485 is compatible with a wide range of
systems. It is easy to integrate RS-485 into existing infrastructures. There
are no specialist skills required to set up and use RS-485 effectively. As
RS-485 is a standards-based protocol, it is easy to find documentation and
support if required.
- RS-485 can support data rates up to 10Mbps and
is able to communicate over distances up to 1200m (data rate is limited at
these distances to 100kbps). RS-485 can be a cost-effective communication
protocol when covering long distances. RS-485 is also immune to electromagnetic
- RS-485 allows use with a serial bus –up to 32
devices can be connected to the communication network of RS-485. This is sometimes
called daisy chaining.
ATC offer RS-485 Communications ports as a standard option
to all chillers to allow continuous monitoring and logging of temperature and
alarms. This allows for remote temperature control –
particularly useful where chillers need to be located a distance from the application.
RS-485 communications can also send signals to trigger an alarm to send in the
event of an error, allowing for the system to be shut off before any costly
When this option is installed, it is then possible to install
a conductivity sensor, a pressure sensor, or a flow meter pack to communicate further information via RS-485. Applied Thermal
Control also offer an option for information be communicated via MODBUS RTU (Remote Terminal Unit) over Ethernet. MODBUS, in simple
terms, is a method used to transmit information between electronic devices over
serial lines. It is usually used to transmit signals to a data gathering system
from instrumentation and control devices.