Excalibur
User Manual
8
9M02-7573-A001-EN
Version 3.0
3.
General
With an OCU and a matching MCU, a machine such as a crane or vehicle can be remotely radio controlled,
avoiding the need for a wired connection between the human interface and the controlled device. Several different
control elements are integrated into the OCU housing so commands to the device securely encode into a radio
transmission. The MCU is then able to receive this transmission, securely decode these commands, and provide
suitable interfaces to drive the machine.
3.1
Radio Transmission
The transmission between the OCU and MCU is performed by means of radio communication. Regarding the
actual radio frequency that is used, there are several radio frequency bands available.
A specific RF frequency band and channel will often have been selected prior to delivery of the system.
Depending on the frequency band, a certain number of RF channels are available.
The OCU and MCU must operate on the same RF channel in order to be able to communicate.
3.1.1 Continuous Transmission
Typically, transmission is continuous and the MCU uses this as part of the information required to maintain the
safety relays in an active state. If the MCU does not receive a valid telegram in this mode for a certain period of
time, it automatically turns off, i.e. safety relays and command relays open. Depending on the application, this
time varies from 0.5 s to 2.0 s.
Note:
In order to ensure optimum communication between the OCU and the MCU, the OCU should always
ideally be operated with line-of-sight transmission to the MCU antenna. Try to avoid total shielding of
the signal path by metallic and other solid obstructions.
3.1.2 Radio Interference
Signals from other RF-emitting sources might interfere with the radio communication between the OCU and MCU.
If the radio link is affected by these sources, changing the RF channel or even the RF band might be necessary.
3.2
Telegram Security
The transmitted telegram contains several security features, as follows:
3.2.1 Frame Type
Each message has an 8-bit message type identifier that is unique to the equipment in use.
3.2.2 System Address
This system uses a 24-bit addressing scheme, where each OCU/MCU pair shares a common, unique system
address. This system address is contained in every telegram sent by the OCU and is checked by the MCU every
time an RF signal is received. The MCU processes a command only when the address in the telegram and the
address stored in the MCU match. This is a safety measure to ensure that the MCU will act only upon its assigned
OCU.
