Caliper, Laser, Miniature
Wednesday, August 30, 2006
A Miniature Laser Caliper has been designed and developed that can measure the ID of tubing as small as 0.280 inch diameter. The Caliper is a non-contact optical device that can operate in clean tubing and in tubing coated with a thin layer of residue or sludge. The Caliper does not touch the deposited material during measurements.
The Caliper consists of a scanhead with an umbilical cord, a line-driver module and an interface electronic unit. The line-driver contains four 3.5 mW Laser Diodes. The Laser Diodes transmit light along the centerline of the scanhead housing through Fiber Optics. Each laser light beam is collimated to 0.02 inches by a gradient index lens. Four 0.04 inch prisms reflect the collimated light beams normal to the axis of the scan head. The laser light beam goes through .030 inch apertures and then to the tubing inner wall. This reflected light beam returns to the scan head through a set of return apertures and is redirected back along the probe's axis. Imaging lenses focus the laser light beams onto a two-axis lateral effect photodetector.
The reflector assembly consists of five bonded custom-made glass elements, four reflector prisms, and a plano-convex lens in a single unit of 0.2 inches width. The four reflector prisms fit together with the concave surfaces and silvered internal mirrors.
Optical triangulation is used to obtain variations in distance between the scan head and the tube wall. Measurements are made by the lateral changes in the laser light beams falling on the photodetector. Four external stainless-steel springs center the Caliper to prevent tube wall (or tube deposit) contact.
Key design features include: 1) Low-power Laser Diodes; 2) Compact (and unique) optical system; 3) ±0.001 inch accurate overfull measuring range and 4) A scan head 0.220 inch OD (can perform in tube IDs as small as 0.280 inch)
Source: Design News, 1992. Reference: James Doyle, Quest Integrated Inc., 21414 68th Ave South, Kent, WA 98032;
Industrial Products
posted by JD52 @ 8:23 PM,
