Which type of flowmeter utilizes a variable orifice to measure gas flow accurately?

The Thorpe tube is a type of flowmeter that utilizes a variable orifice to measure gas flow accurately. In a Thorpe tube, the flow of gas passes through a tapered tube that has a float inside. As the gas flows, it carries the float upward to a level that corresponds to the flow rate, effectively creating a variable orifice in which the diameter of gas flow increases as the float rises. This design allows for a precise measurement of flow rates, making it a common choice for medical applications where accurate gas delivery is crucial, such as in respiratory care.

The concept of a variable orifice is fundamental because it adjusts the size of the path through which gas flows in response to changes in flow rate, ensuring that the measurement reflects the actual flow accurately at different pressures. This feature sets the Thorpe tube apart from other devices, which may not provide the same level of specificity or responsiveness to varying conditions.

In comparison, the Bourdon gauge measures pressure instead of flow and operates on a coiled tube mechanism. A flow restrictor simply reduces flow without measuring it, and a pressure uncompensated Thorpe tube is a variant that does not account for changes in pressure, which can affect flow readings. The unique characteristics of the Thorpe tube