1. Summary of the issue
The Lane Survey Wizard within the RT-Range software is used to survey lanes on testing tracks for the purpose of producing map files of the tracks to be used with the RT-Range system. A trigger switch, mounted on the OxTS trolley can be used with an RT unit to add map points at the chosen locations, when the option to automatically add points to the map is considered not suitable.
The trigger switch used with the RT unit can cause the generation of several overlapping points on the map for a single button press, due to switch bounce. Different trigger switches have their own characteristics, which can produce inconsistent behaviour.
The RT units have internal circuitry to deal with switch bounce, however it is not fully effective.
2. Summary of investigations results
- The issue is caused by irregularities (bounces) in the signals generated by the switch as a result of momentary bouncing between in-contact and not in-contact as the switch opens or closes.
- The switch bounces may be counted by the RT as multiple, separately generated triggers, hence resulting in multiple overlapping points being added to the map.
- The issue only involves the mechanical, manually-operated trigger switches. Electrically generated trigger signals showed no bounces.
- The signals generated by the rising edge of triggers were proved to be consistently worse-performing i.e. showing many more bounces, than signals generated by the falling edge of triggers.
- Up to the RT-Range software version 170607, the RT-Range Lane Survey Wizard utilised the signals generated by the rising edge of triggers to add points to the maps. It did not allow users to select which edge to use during the survey operations.
- In the switch usually supplied by OxTS with the RT-Range products, the falling edge occurs when closing the switch, while the rising edge occurs when releasing the switch. Other switches might show a different behaviour.
- A new release of the RT-Range software is modified to use the signals generated by the falling edge of triggers to create map points for survey and map-creation operations. Signals generated by the rising edge of triggers are no longer used in the new RT-Range software.
Using the standard switch supplied by OxTS, the falling edge of trigger signals corresponds to closing the switch.
- When using the RT2000, RT3000, RT4000 products, multiple triggers can be successfully and consistently removed from the signals generated by manual switches by using specific advanced commands added to the RT unit configuration. The purpose of these advanced commands is to prevent the RT unit from logging multiple trigger signals.
4. Actions required by users
The only actions required by users to obtain a problem-free lane survey experience are:
- Rely on the trigger-signals generated by the falling edge of triggers by installing and using the latest RT-Range software, version 180820
- Remove any residual bounces from the trigger signals by adding the following advanced commands to the configuration of the RT unit used in the survey:
->gps1: UNLOG COM2 MARKTIMEB
->gps1: UNLOG COM2 MARK2TIMEB
This can be done in NAVconfig > Options > Advanced .
NOTE: The above advanced commands should be added to the RT unit configuration only in cases where a manually operated switch is utilised. They should not be applied where the trigger signals are electrically generated.
A consequence of the advanced commands is to make the timestamp applied to the triggers slightly less accurate (in the order of hundreds of microseconds). As these commands are only applicable to cases of manually operated switches, there should not be any tangible negative effect.