<< Graham -- re your question on fuel gage design:
<< BTW, isn't there a minimum current required to create a spark with enough
energy to ignite fuel vapour. Current limiting should give adequate safety.
>>
>>
The formal name for this is "intrinsically safe" meaning it won't ignite a
mixture of gas and air proportioned for maximum sensitivity. Over here one
would get the curves for this from UL or CSA publications -- there must be
equivalent institutions in the UK although I don't know what they would be.
The idea with intrinsically safe instruments is that the complete instrument
would be immersed in the explosive atmosphere, where it must not cause
ignition under any circumstance. Generally this means that currents are
limited to a few mils, voltages are less than about 40v and capacitors and
inductors are limited in size to minimize energy storage.
In a previous life I designed "smart" pressure transmitters for application in
natural gas applications (explosion proof rather than intrinsically safe) but
didn't keep much technical info when I retired so can't give reliable values
for ignition points and component values.
Regards, John A044
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