The crystal controlled transmitter uses an 8-bit micro-controller, operating at 2.5 MHz, to scan the command switches. All major function switches must be in the center or “off” position before the crane remote control Main Contactor can be energized. When the transmitter is”on” and the command switches are “off” or centered, then the transmitter actually sendsa “stop” command to the system. Motion can occur only with the removal of the “stop” command and the addition of a speed point/directional command within a certain timesequence. Using the key-switch to turn off the transmitter power causes the transmitter tosend five consecutive “E-STOP” messages before shutting down.
The switch position data is transmitted as a digital signal at the licensed frequency, using Manchester II coding. The digital message has a specific format and is repeated 2 to9 times per second. The repeat rate is programmable. The transmitter is turned off between messages to conserve battery life and rf spectrum. This makes it possible to have several transmitters operating in the same area, on the same frequency, with practically no interference because of the different transmission rates. The unique address code of each transmitter and receiver assures that only the matching receiver responds tothe radio commands. All other signals on the same frequency are ignored.
The use of Manchester II (bi-phase) digital FM signal coding makes the message less sensitive to corruption from interference. Please consult Tech Info 31.100, page 2, for adetailed discussion on the message format and Manchester II coding.
The security of any remote control system is of the utmost importance.
Crane Remote Control systems’ security is enhanced through multiplechecks before any function can becomeoperational:
• The received signal must be of the properfrequency.
• The received message must have the proper address and must be in the correct format.
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