What should the machine do if the wireless remote control signal is lost?
When the signal is cut the receiver releases its outputs on timeout and movement stops; the machine does not restart by itself when the link returns.
When the signal is lost the machine must stop moving and go to a safe state. The receiver detects within a defined period that the flow of valid packets has stopped and releases its outputs; when the connection comes back, no movement begins until the operator gives a new command. This is not an extra feature but a basic design requirement of a wireless remote control.
Loss of signal is an unavoidable operating condition: the battery runs out, the operator goes out of range, a stack of containers gets in the way, a nearby inverter fills the band. The job of the design is not to prevent this but to behave predictably when it happens.
The four elements of the expected behaviour
- Timeout: the receiver cuts the movement within a defined period after the flow of valid packets stops. On the HCT402, for example, this period is 250 ms; the motor goes to the safe neutral position and the oil flow stops.
- Safe default state: the outputs return to a de-energised or neutral position; no movement continues in the absence of a signal.
- No automatic restart: when the connection comes back the machine must not move by itself; the operator has to give a deliberate command.
- Architecture: the stopping chain must be designed so that a single fault does not cause the function to be lost.
What this expectation rests on
Not a single standard but several complementary texts describe this behaviour. EN 13557 deals with control devices and control stations on cranes; it requires stopping on loss of signal in wireless control, treats the stopping function in its annex as a safety-related control part and calls for a category 3 or higher design. EN 60204-32:2008 frames the electrical equipment of hoisting machines, while EN 13135:2013+A1:2018 frames the selection of that equipment. For the behavioural requirements of the wireless side itself, IEC/EN 62745 is the text to read.
Loss of signal and releasing the button are not the same thing
When you release the button the transmitter sends a “stop” message; on loss of signal nothing arrives at all and the receiver has to interpret that silence for itself. The stopping time is not the same either: on releasing the button the delay is the time the command takes to arrive, whereas on loss of signal the timeout period is added on top of that. On a system working with momentary control logic this difference is small; on an installation that runs by latching its output, on the other hand, the loss of signal behaviour becomes the only layer of protection. Do not use latched outputs on crane movements.
Commissioning test: what to do and what to look at
| Test | How it is done | Expected result |
|---|---|---|
| Removing the battery | Take the battery out of the remote control while the movement is running | The relay releases, the movement stops |
| Out of range | Move away from the machine while giving a command | The response first becomes intermittent, then the movement stops |
| Restart | Power up the remote control while holding a button down | The machine must not move |
| Receiver supply | Cut the receiver supply and restore it | The outputs release and do not pull in by themselves |
You can usually tell by ear whether the relay has released; if you hear no click, measure the contact. Do the tests together with the behaviour at the edge of the range and repeat them at every commissioning.
Stopping the movement does not solve everything
Loss of signal stops the movement, it does not lower the load. On an electric hoist the load stays hanging on the brake; on a hydraulic lever the valve returns to neutral but the load in the cylinder stays where it is. On a load with inertia the movement carries on for a while after the output is released; measure this stopping distance during the acceptance test and lay the working area out accordingly. Nor is it guaranteed that the operator will notice the loss of signal; without an indicator the person carries on pressing the button. For these reasons the loss of signal behaviour does not take the place of the wired emergency stop circuit on the site.
Be sure to try the battery removal scenario in the acceptance test; it is the step most often skipped. If you cannot observe the expected behaviour, do not commission the installation; first confirm the timeout and restart behaviour of the set from the manual.
The full topic: Wireless remote control installation: pairing, relay, safety