How Comparative Vacuum Monitoring Works
The Basic Principle
The principle behind CVM™ is uniquely simple; a vacuum contained in a small volume is extremely sensitive to any leakages.
The CVM™ principle relies on placing a sensor onto the surface of a component where damage is expected to occur. The sensor contains a manifold of fine channels that are open to the surface. Once the sensor has been installed on the surface, the channels form closed “galleries” to which a vacuum can be applied. It is important to note that the surface of the component forms part of the sensor system, with the crack itself providing the leakage path for air into the vacuum galleries (Figure 1).
The sensor is connected to a vacuum source through an accurate flow meter. Figures 2. and 3. show a schematic of the equipment used in laboratory trials which allows continuous monitoring of a sensor, or several sensors connected in series or parallel (not shown). If there is no damage on the component, then the vacuum in the sensor will be approximately the same as the vacuum source (Figure 2.) If however a crack develops, a leakage path will exist and the vacuum level will be reduced in the sensor manifold (Figure 3.)
A schematic of a simple CVM sensor.
CVM system installed on an intact component.
CVM system installed on a damaged component.