Sensor caliper

In the ultrasonic caliper sub, two ultrasonic sensors are mounted 180° apart on stabilizer blades as shown in Figure 4-288. 

Figure 4-288. MWD ultrasonic caliper (a) sensor in the stabilizer blades (b) schematic of the echoes. (Courtesy Anadrill [113].J...

To select the correct sensor you should know something about how the different sensors work (accuracy, repeatability, environmental effect, etc.), and which is used for what application. This is important since not all sensors measure the same way. The three most common sensors used down-stream is nuclear, infrared, and caliper. There are also specialized types such as microwave, laser, X-ray, and ultrasonic. They... 

Computer-controlled automatic profile dies with electrical controlled sensors in closed-loop control systems have developed greater efficiency and accuracy to extrusion coating, cast film, and sheet lines. A scanner measures the web thickness and signals the computer, which then converts the readings to act on thermally actuated die bolts. The individual adjusting bolts expand or contract as ordered by the computer to control the profile. The more sophisticated systems measure adjusting bolt temperature and provide faster response time with less scrap and quicker startups. The scanner is typically an infrared, nuclear, or caliper-type gauge. 

As mentioned above, modern brake systems typically have two or more independant brake systems, each consisting of individual and independant E/E/PE control systems, hydraulic pressme control systems, brake calipers or groups of calipers and speed sensors. 

As the slider moves it reads the position of the tracks under the sensors and calculates its current absolute position. This eliminates the need for having to reset the caliper to zero before use. 

Air bearing caliper measurement The sensors are mounted onto flat measurement plates with a diameter of roughly 60 mm. Those plates are drilled, with pressurized air coming out of the tiny holes. The plates are pressed towards the paper from both sides. The distance of the plates from the paper is controlled by the air flow. The distance between the plates is measured using an electromagnetic field. 

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