The only thing a sender of oil can put out is a VARYING RESISTANCE.
It is a tiny unit containing a PIEZZO CRYSTAL, these work like a sort of squeeze for power, in that the harder they are compressed, the more voltage they will allow to flow, in this case it allows the flow of neutrons.
It is WHOLLY as said by billabong, pressure exerted on the crytstal contained within the unit(sender) equals resistance, and hence guage reading.
The sender contains NO circuitary at all, other than the crystal.
tabetha