Which instrument measures the difference between initial pressure and the loss of pressure?

The instrument that measures the difference between initial pressure and the loss of pressure is the differential pressure (dP) cell. This device is specifically designed to measure the pressure difference between two points in a system. It works by taking inputs from two pressure taps, one at a high-pressure point and another at a low-pressure point, allowing it to capture the change in pressure between those two locations.

Differential pressure measurements are crucial in various applications, including flow measurement, liquid level detection, and filter monitoring. The dP cell's ability to translate the pressure differential into a readable output makes it an essential tool in process control and instrumentation.

Other instruments mentioned serve different purposes. An orifice plate measures flow rate by creating a pressure drop, but it does not solely measure the difference in pressure as the dP cell does. A flow meter measures the rate of flow rather than pressure differences, and a capacitance sensor is generally used for level measurement, depending on changes in capacitance in response to level variations, rather than pressure differentials. Thus, the dP cell is uniquely suited for directly measuring the difference in pressure, which is why it is the correct choice.