Surface Plate Calibration
Surface plate calibration is the only sure way to know you are working with a level surface and can expect accurate workmanship when using your granite surface plates. Surface plates wear with use and must be properly maintained to ensure flatness and continued precision measurement. Granite surface plate calibration includes checking for wear and deviation from the grade requirements. In many cases, proper resurfacing can bring the surface of the plate back within flatness tolerances. Flatness tolerances for standard grade surface plates AA, A and B are defined in federal specification GGG-P-463c.
Granite surface plate calibration should be performed routinely to maintain the proper flatness and ensure measurement accuracy over time. The intervals between each surface plate calibration should be based on the frequency of use, the condition of the environment where the surface plate is located and your company’s quality requirements. Regular cleaning and covering when not in use, as well as light usage will generally allow for longer intervals between each calibration.
Calibration performed by LTI Metrology is A2LA accredited and the equipment used by our technicians has a NIST traceable calibration. A Calibration Certificate is provided with all calibration showing results, grade requirements, any work completed to restore flatness, and “as found” and “as left” conditions. Our field team can also calibrate measuring hand tools and various equipment including optical comparators, hardness testers, ovens and furnaces, scales and more. Service for many additional instruments is performed in our environmentally-controlled laboratory in the Philadelphia PA (USA).
The Surface Plate Calibration Process
The field team at LTI Metrology provides on-site granite surface plate calibration and resurfacing. During surface plate calibration, our technicians will measure both surface flatness and repeatability by taking measurements in locations across the surface. These reading will be used to determine deviation from the guidelines set for the grade of surface plate. Once low areas are identified, we will resurface the plate to restore flatness.
Both flatness and repeatability readings are critical steps in granite surface plate calibration to insure a precision surface that provides accurate measurement. Flatness is measured using points on the surface contained within two parallel planes, the base plane and the roof plane. The measurement of distance between the planes is the overall flatness of the surface.
Repeatability is verified by measuring various local flatness areas across the surface to help guarantee that a measurement taken anywhere on the surface of a plate will repeat within the stated tolerance.
LTI’s technicians measure surface plate wear with a computerized calibration system using differential leveling feet. This system provides reliable surface evaluation with detailed diagrams showing measurement readings clearly explaining wear and deviation from the grade accuracy specification. When needed, lapping or resurfacing is provided to bring measurements within grade guidelines. This procedure involves polishing the surface with an abrasive paste to remove all unwanted material. Our field service technicians have the ability to resurface to any grade needed by your quality system.
Granite surface plate calibration provided by LTI Metrology also includes cleaning and a light polishing. When needed, the field team also provides granite repair to fix any chips on the surface plate.
LTI Metrology Capabilities
- On-site surface plate calibration
- Calibration includes resurfacing, cleaning, light polishing and repair, when needed
- Surface plates up to 14 ft. diagonal
- Detailed diagrams with measurements explaining deviation from grade specifications are provided