Ultrasonic Arrays developed the first non-contact ultrasonic thickness gage in 1984. This gage, the TMS-1000 was developed to overcome the inherent problems in attempting to use contact and laser measuring devices in process applications.

This gage was revolutionary in that it was self calibrating for any factors that would affect measurement accuracy, even for fixture movement. An external reference bar target was used as a standard to eliminate variables that affected the speed of sound (such as temperature).

High frequency ultrasound is transmitted from the sound producing surface to the reference bar and back, 125 times per second. If the distance to the reference bar changes, this means that the speed of sound has changed. The microprocessor in the gage automatically corrects the measurement.

Most of the sound passes the transducer reference bar(s), and travels to the product surface and returns to the transducer receiver.

The thickness measurement is equal to the separation of the transducers S less the distance measured to the top surface d₁ and to the bottom surface d₂. The separation S is constantly measured and compared to what S was when the transducers were originally calibrated, correcting for any fixture movement.

In a process line, the temperature swings caused by the process and ambient temperature variation between the hot part of the day and the cold part of the night can easily be 50 degrees F. This means that the structures of the line, including the fixtures supporting the sensors are moving. Fixtures can also move for other reasons, including collisions with product, personnel standing on the fixtures for maintenance, being bumped with a fork lift, internal stress relief in the fixtures, etc. UAI's patented AutoZcal feature, automatically corrects for movement, no matter what the cause.

Another very important reason why the TMS series of non-contact gages are so accurate is the supplied "air service". In a mill environment there are thermal air currents that affect the speed of sound. In addition products themselves may be at varying temperatures. These elements cause inaccuracy and instability in the measurement. The UAI air service which is provided with every gage, acts as a wave guide to eliminate the effects of thermals. In the TMS series the ’air service” consists of an air filtration system, air supply and air lines to condition the sound path and protect the sensors.