| 摘要 |
<p>Liquid level sensing apparatus for a liquid storage tank (46) with a vapour region (48) and a fluid region (50) includes first and second sensing tubes (42,44) exposed to the vapour region (48) and fluid region (50), respectively. A pump (40) with an inlet and an outlet is included, the inlet is pneumatically coupled to the first sensing tube (42) and the outlet is pneumatically coupled to the second sensing tube (44). First and second controllable valves (32,34) each have a first input. The first input of the first controllable valve (32) is pneumatically coupled to the first sensing tube (42) and the first input of the second controllable valve (34) is pneumatically coupled to the second sensing tube (44). The first and second controllable valves (32,44) each also have a second input pneumatically coupled to atmosphere (36,38), wherein each of the controllable valves (32,34) has an output that is selectively pneumatically coupled to either the first input or second input of said valve. A transducer (16) is coupled to the outputs of the first and second controllable valves (32,34) so that the transducer (16) may be selectively coupled either to atmosphere or the sensing tubes (42,44). <IMAGE></p> |
