Final answer:
Pressure measurement using a bellow sensor relies on the expansion and contraction of a bellow in response to external pressure changes, with the movement translated to a mechanical indicator. Key concepts include gauge and absolute pressure, and for blood pressure measurement, adjustments for hydrostatic pressure due to height differences should be considered. A detailed diagram would help illustrate the mechanics of the bellow sensor and its use in pressure measurement
Step-by-step explanation:
Explaining Pressure Measurement Using a Bellow Sensor
To explain pressure measurement using a bellow sensor, it is crucial to start with the gauge pressure and absolute pressure understanding. A bellow is a flexible sealed container that expands or contracts with the changes in pressure exerted externally. The inside of the bellow is typically evacuated or filled with a set pressure of gas, which means that any change in external pressure causes a mechanical deformation of the bellow.
Bellow sensors are commonly used for measuring low pressures and can be set up in an aneroid gauge. The basic principle is that the bellow expands or contracts with changes in pressure. This motion is then transferred to a mechanical indicator, typically a needle on a dial, to give a visual display of the pressure level.
Figure 11.18, which is a reference provided for these discussions, indicates how an aneroid gauge, which utilizes a bellow, functions. When there's an increase in external pressure, the bellow contracts, and the connected mechanical indicator moves. This indicates a higher pressure reading on the gauge. Conversely, when the external pressure reduces, the bellow expands, which is indicated by a lower pressure reading on the gauge.
To measure blood pressure using this concept, a cuff with an integrated bellow sensor can be placed on a person's leg. For a person with a blood pressure of 120 over 80 mm Hg at the heart level, measuring at 0.500 m below would involve adjusting the reading for hydrostatic pressure due to the height of the blood column.
Drawing and Understanding the Pressure Measurement System
The diagram would represent the bellow attached to a mechanical system, which includes a needle and a calibrated scale to indicate pressure. When measuring pressure changes, as in example 33, the change in external pressure, due to height difference in the circulatory system, causes the bellow to either expand or contract, resulting in the needle moving and providing a reading in mm Hg that accounts for the additional pressure exerted by the height of the blood column.