Latency
Latency is the total time between the operator pressing the button and the machine output moving. Packet time on air, retries, receiver processing time and the response time of the output element all go into this total. In a remote control the critical direction is not pressing but releasing.
The main items contributing to total latency are these:
- Key scanning and packet preparation: usually a few milliseconds.
- Time on air: depends on packet length and data rate; for short remote control packets it is on the order of tens of milliseconds.
- Retries: under interference these can multiply the total time.
- Output element: relay pull-in time or valve opening time is added.
A small delay at the start of motion is mostly unnoticeable to the operator; but a delay in stopping when the button is released is directly a safety matter. That is why stopping is not left to the retry mechanism; a timeout takes over when no valid packet has arrived for a defined period. On the AXI side, the dump data states a latency below 1 second for the XRF protocol; on the HCT402 the signal loss timeout is defined as 250 ms, and within that time the motor goes to the safe centre position.
Context where this term is used: Wireless remote control installation: pairing, relay, safety