C-Type

In this, the process pressure is connected to the tube support end of the tube, while the tip end is sealed. Because of the difference between inside and outside radii, the Bourdon tube presents different areas to pressure, which causes the tube to tend to straighten when pressure is applied.

The resulting tip motion is nonlinear because fewer motion results from each increment of additional pressure. This nonlinear motion has to be converted to linear rotational pointer response. This is done mechanically by means of a geared sector and pinion movement. The tip motion is transferred to the tail of the movement sector by the connector link. The angle between the connecting link and the sector tail is called the traveling angle. This angle changes with tip movement in a nonlinear fashion, compensating for the nonlinearity of the tip movement. It is designed to minimize backlash and provide smooth roll-on and roll-off characteristics in the geared sector. It is also designed to provide pinion movement by using fine pitch gears or by eliminating the gears altogether and using a cam sector that positions on a roller surface.

This design eliminates the gears that eventually wear out and reduces the play that occurs when teeth are worn. On gear and pinion designs, the operation has been improved using nylon and Teflon materials.

Ni-Span C seamless tubing is the best choice for Bourdon tube applications in all cases except those at extremely high pressure or those that are extremely corrosive. Direct indicators or motion balance transmitters using C-Bourdon elements are available with spans from 0–15 PSI to 0–20,000 PSI (0–100 kPa to 0–140 MPa) and can be used for positive, negative, or compound pressure ranges, but the indication on the vacuum side will not be accurate or sensitive. The accuracy of these devices is a function of the Bourdon tube diameter, design quality, and calibration procedures. It can vary from ±0.1 to ±5% inaccuracy, with most of these units failing in ±1%.

List of Prominent Suppliers: Afrisco, Ashcroft, Burkert, Dwyer, Noshok, Omega, PCI Instruments, Prisma, Schmierer, Trafag, Winters, WIKA