Communication Monitoring (Watchdog)
The monitoring mechanism by which the receiver continuously measures the time between valid frames arriving from the transmitter and drops its outputs on a defined timeout. Every valid frame resets the counter; if the counter expires the system treats it as signal loss and goes to the safe state.
The watchdog is the most fundamental safety element of a wireless remote control, because there is no other way of knowing that the radio link has broken. The transmitter sends a command frame at regular intervals for as long as the button is held. The receiver counts these frames; if several consecutive frames fail to arrive, a timeout occurs.
- Only valid frames count: a packet with the wrong address or one that fails the integrity check does not reset the counter.
- Balance of tolerance: stopping on a single lost frame produces intermittent operation; too much tolerance lengthens the stopping distance.
- Resulting behaviour: on timeout all motion outputs are released simultaneously.
The easiest way to observe this mechanism in the field is this: switch the transmitter off with no load and you will hear the receiver relays drop out after a short delay. This delay is normal and part of the design. Since the time is not stated in the product data of the AXI sets, do not assume a value; confirm it from the manual and add this test to your periodic tests.
Context in which this term is used: Wireless Crane Remote Control Selection Guide