**Bourdon Gauge Measures Gauge Pressure**

A Bourdon gauge is a type of pressure measurement device commonly used in various applications, including mechanical engineering. It is a mechanical instrument that operates based on the principle of elastic deformation.

**Understanding Gauge Pressure:**

Before diving into the explanation of why a Bourdon gauge measures gauge pressure, it is essential to understand what gauge pressure is. Gauge pressure is the pressure measured relative to the local atmospheric pressure. It represents the pressure above or below the atmospheric pressure at a specific location.

**Bourdon Gauge Principle:**

A Bourdon gauge consists of a curved, hollow, elliptical tube called the Bourdon tube. This tube is made of a highly elastic material, such as bronze or stainless steel. One end of the tube is sealed, while the other end is connected to the pressure source.

When pressure is applied to the open end of the Bourdon tube, it causes the tube to deform and straighten out. This deformation is proportional to the applied pressure. The Bourdon tube is connected to a mechanical linkage system that converts the linear motion of the tube into rotational motion.

**Working of a Bourdon Gauge:**

1. Pressure Application: The open end of the Bourdon tube is connected to the pressure source through a connecting pipe. When pressure is applied, it enters the Bourdon tube.

2. Tube Deformation: As pressure enters the Bourdon tube, it causes the tube to deform and straighten out. The extent of deformation depends on the applied pressure.

3. Rotational Motion: The Bourdon tube is connected to a mechanical linkage system, which typically includes gears and a pointer. As the tube straightens out, it causes the mechanical linkage to rotate.

4. Reading the Gauge: The rotational motion of the mechanical linkage is translated into the movement of a pointer on a calibrated scale. The scale is marked with units of pressure, such as psi or kPa.

**Why Bourdon Gauge Measures Gauge Pressure:**

The Bourdon gauge is designed to measure pressure relative to the local atmospheric pressure. When the pressure is applied to the Bourdon tube, it deforms and straightens out. This deformation is proportional to the difference between the applied pressure and the local atmospheric pressure.

Since the Bourdon gauge is calibrated to read zero when the pressure is equal to the local atmospheric pressure, it effectively measures the pressure above or below the atmospheric pressure. Therefore, the Bourdon gauge measures gauge pressure.

In conclusion, a Bourdon gauge measures gauge pressure, which represents the pressure relative to the local atmospheric pressure. It operates based on the principle of elastic deformation of the Bourdon tube, which is proportional to the difference between the applied pressure and the atmospheric pressure.