CAN-bus data - Live if ignition turned off?

[Chalwyn1]

I am using a CANM8 connect RPM interface to pick up an RPM signal from the CAN-bus system and convert to a Hz output that is compatible with our speed switch. Can anyone confirm if the Can-bus signal will continue to be live and produce this signal if the key is removed from the ignition but the engine is still running.

I install a shut down device on diesel engines that work in hazardous areas to control a runaway caused by hydrocarbons. The device is controlled using a module that picks up a speed signal from the alternators W terminal so works even if the ignition is off and the engine speed increasing. Modern automotive alternators are becoming more inaccessible so am looking for an alternative source for the speed signal but am concerned that the signal may be lost through CAN bus if key is removed?

Thanks

[Chalwyn1]

So if the CAN-bus network gives an rpm output when ignition is off will depend on the manufacturer and is not standard for all vehicles? I have not had much luck getting a response from the couple of manufacturers I have contacted and as far as I know there is no way of testing this scenario.

[Chalwyn1]

Our system closes a butterfly valve in the engines air intake system to stop the engine in the event of a runaway caused by an external fuel source such as hydrocarbons produced an oil and gas sites.

The speed signal we currently use comes from the alternator which continues to produce an output if the ignition is off and engine turning, an alternative source for this speed signal needs to be 100% guaranteed so looking at the CAN-bus data to see if this is a possible option - but not if signal is lost when key removed