USER MANUAL
TYPE ML-2012/13
Manufacturers of low power instruments
page 19
4.4 RS485
RS485 is a serial bus-system, which uses 3 wires for its communication. It uses a “differential balanced
line”, which can span relatively large distances (up to 4000 feet (1200 m)). A rule of thumb is that the
speed in bit/s multiplied by the length in meters should not exceed 10
8
. Thus a 50 meter cable should not
signal faster than 2 Mbit/s.
Instead of RS232, RS485 is capable of communicating with more than one device. After all, it is a bus-
system.
RS485 sensors are called “slaves” and must have their unique address. The ML-2012/13 acts as a
master and retrieves the information from the slaves. Only one slave can respond to the requests of the
master at a time.
To set up your RS485 sensor for use with the ML-2012/13, make sure that the address is programmed
correctly, and that the sensor address is unique.
Figure 1: RS485 Wiring
RS485 is often used with MODBUS/RTU-sensors, and is less susceptible for Electrical interference than
RS232.
Your ML-2012/13 has one RS485 port which is capable of driving multiple sensors (maximum amount of
sensors depends on specs from the manufacturer of the sensor, a practical figure is 10. The maximum
amount of slaves, defined by EIA/RS485 is 32). For the exact number of sensors you can connect to your
ML-2012/13 see chapter
Firmware Driver limitations
We recommend using twisted pair cable to connect to the sensors.
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