These pressure sources are measured by two independent but matched Bourdon tubes, housed within an aluminum case. 压力源通过两个独立但相配的波尔登压力计加以测试，该压力计安装于铝合金箱中。
It is possible for the feed system to have a low impedance, looking downstream from the pressure source at a certain frequency. 在压力源下游，供应系统在某一频率下可能有一低的阻抗。
