A history of the evolution of this breakthrough bourdon material.
One of the most unique and sophisticated pressure sensors is the fused quartz bourdon tube or capsule. The fused quartz bourdon tube should not be confused with the quartz resonator pressure sensors, which use quartz crystal and are currently designed and marketed by companies such as Paroscientific and Quartzdyne. Fused quartz tubing is manufactured by melting naturally occurring high purity quartz crystals at approximately 2000°C and then extruding the melted quartz into various diameters and wall thicknesses. This type of tubing is transparent and looks almost like glass.
Some of the early developments of the quartz bourdon can be traced back to Sam Worden, who was most noted for his pioneering work in gravimeters. The Worden Gravity Meter has the capability of measuring relative gravity to 1 part in 100 000 000 or a difference in elevation of only 25 mm. Before Sam Worden started fabricating quartz bourdon tubes for Ruska Instruments (early 1960s), he built some low resolutions models for use in scientific labs.
Many would ask why fused quartz was chosen to be a pressure sensing element. Dating back to the use of fused quartz in gravimeters, it was well known that it made an almost perfect spring material. Since fused quartz had a very low coefficient of thermal expansion, low thermoelastic modulus and low internal viscosity the stage was set to use fused quartz as the breakthrough bourdon material.
In 1953 Texas Instruments (TI) in Houston, acquired Houston Technical Labs from Sam Worden. At TI, design and development efforts by J.B. ‘Pete’ Damrel Jr. and Jerry Fruit led to the introduction of the Model 140 and 142 in the early 1960s. TI’s brochure for ‘Fused Quartz Precision Pressure Products’ (dated January 1964) announced ‘New Concepts in Precision Pressure Measurement and Control’. These breakthrough pressure instruments were targeted at the existing market for mercury manometers and dead weight testers. TI’s new products offered improved resolution, respectability, hysteresis and portability over conventional pressure measuring instruments in the early 1960s. The resolution of these original TI instruments was 1 part in 100 000.
At the base of the quartz bourdon tube was a mirror that was used to detect the deflection of the tube when pressure was applied. A light source aimed at the mirror reflected back on to a pair of photocells that indicated the amount of angular deflection. A mechanical digital counter would indicate the amount of offset from null. The counter reading multiplied by a scale factor provided a number that was proportional to the pressure applied to the bourdon tube.
The TI 140 Series quickly found applications in avionics, calibration laboratories, and other applications that required a high level of accuracy and performance. The early TI bourdon capsules were capable of measuring pressures up to 500 psi and could be used to measure gauge, absolute or differential pressure.
Another important TI product introduction was the precision pressure controller that could provide automatic pressure control or generation. Models were designed to be used in conjunction with the new TI precision pressure gauges. The quartz bourdon tube was designed to be interchangeable so that the end user could easily install and remove tubes for different pressure ranges. The TI ‘Precision Pressure Gauge’ was patented in 1966 and marked the first commercialisation of a precision fused quartz bourdon tube.
The author has dedicated this article to the pioneers that forged the ‘technology trail’ for the fused quartz bourdon tube in precision pressure instruments. Wika SA’s marketing manager, Greg Rusznyak, describes it as ‘fascinating reading for someone interested in high precision pressure calibration and the history thereof’. Readers interested in the subsequent ‘technology trail’, the ‘characters’ involved and how it eventually found its way to Mensor Corporation can visit: http://instrumentation.co.za/+C14114
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