he Dakota Ultrasonics model MX-3 is a precision Ultrasonic Micrometer. Based on the same operating principles as SONAR, the MX-3 is capable of measuring the thickness of various materials with accuracy as high as ± 0.001 inches, or ± 0.01 millimeters. The principle advantage of ultrasonic measurement over traditional methods is that ultrasonic measurements can be performed with access to only one side of the material being measured.
While the MX-3 excels at making single point measurements, it is sometimes desirable to examine a larger region, searching for the thinnest point. The MX-3 includes a feature, called Scan Mode, which allows it to do just that. In normal operation, the MX-3 performs and displays four measurements every second, which is quite adequate for single measurements. In Scan Mode, however, the gauge performs sixteen measurements every second. While the transducer is in contact with the material being measured, the MX-3 is keeping track of the lowest measurement it finds. The transducer may be "scrubbed" across a surface, and any brief interruptions in the signal will be ignored. When the transducer loses contact with the surface for more than a second, the MX-3 will display the smallest measurement it found.
When the gauge is making a measurement, six or seven of the bars should be on. If fewer than five bars are on, the MX-3 is having difficulty achieving a stable measurement, and the thickness value displayed will most likely be erroneous.
While the transducer is in contact with the material being measured, the MX-3 will perform four measurements every second, updating its display as it does so. When the transducer is removed from the surface, the display will hold the last measurement made.
In order for the MX-3 to make accurate measurements, it must be set to the correct sound-velocity for the material being measured. Different types of material have different inherent sound-velocities. For example, the velocity of sound through steel is about 0.233 inches-per-microsecond, versus that of aluminum, which is about 0.248 inches-per-microsecond. If the gauge is not set to the correct sound-velocity, all of the measurements the gauge makes will be erroneous by some fixed percentage.