CT24 MCU
User Manual
11
9M02-7608-A001-EN
Version 2.0
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. A number of
different control elements are integrated into the OCU housing so that 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. With regard to 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, the
time varies from 0.5 s to 2.0 s.
In order to ensure optimum communication between the OCU and the MCU, ideally operate the OCU with line of
sight to the MCU antenna at all times. Avoid total shielding of the signal path by metallic and other solid
obstructions.
In some configurations, the MCU may be configured to operate safely in the absence of RF signal, much as a
safety PLC will do. Such applications are strictly defined.
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.
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, with each OCU/MCU pair sharing 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 a 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.
3.2.3 CRC
The telegram is checked for integrity using a 16-bit CRC; frames containing mismatched CRC will be rejected.
