6
This example picture illustrates how the base station can be connected to an RMD680 / RMD681
transmitter by sharing one 24 VDC power supply.
RS-485 bus information
RS-485 is a serial bus type commonly used in the industry. It is based on two data lines D0 and D1,
which are connected in
parallel
with all the devices connected to RS-485 bus and D0 and D1 pins. To
even up the electric potential between different devices, a third wire is also needed. In the above
example picture the blue ground wire evens the potential differences between the devices. Branches in
the bus should be avoided, in other words the bus cabling should circulate through all the devices
without branches. The maximum recommended length of the bus is 1 km. The cable should be twisted
pair and the wire diameter should be at least 0.5 mm.
To ensure EMC compliance the RS-485 bus cable should no more than 30 meters long.
The bus is bidirectional. Only one device at a time can send data, during which other devices listen.
Only one device connected to the bus is set as master, in other words as a chairman, which starts all
conversations on the bus. Other devices are slaves and they only answer to queries of the master. Each
device connected to the bus has its unique bus address, which the master device uses to direct its
commands to a specific device.
The base station functions as an RS-485 bus-master and queries the measurement data from other
devices on the bus. In a typical application, such as the one presented in the diagram above, the base
station regularly queries the RMD680 / RMD681 transmitter’s measurement data and sends it to the
Ovaport server.
Radio receiver antenna connector
The base station top part has the radio receiver’s female BNC connector. The base station is supplied
with a suitable antenna. Attach the antenna to the connector to complete the installation.
The base
station
24 VDC
PSU
