Precision Metrology of Parallel Surfaces on Oil & Gas Flowmeter

October 1, 2014

 

 

Machinists know the tools they trust on a granite table to measure precise distances. Many are purely mechanical gauges with decades-old technology that set the standard to this day with surprising accuracy and precision. That's the challenge that faced an Oil & Gas giant when they considered switching from single-point mechanical measurements to non-contact laser metrology gauges to measure their products in 4 places simultaneously. Despite the potential of lasers to measure with nanometer resolution, would they have the accuracy and precision of a mechanical gauge? The client turned to Keyence who asked Cyth to help do some validation.

 

Measuring height or parallelism is a common measurement after a product has been machined.  The product is the aluminum body of an oil or gas flowmeter, which contains a precision impeller mounted on bearings with such precision and balance that literally a gentle human breath can make it spin.  To achieve industry-leading performance and near-zero friction, the opposite machined surfaces require unparalleled parallelsim (pun intended).  While one surface is flat on a granite table, the other surface needs to be measured at least at 3 points to confirm the length of the body as well as the parallelism.  Three points are enough to define a plane.  The design of the system was chosen to setup four Keyence LK Laser Displacement Sensors with 0.0001" resolution (0.1 Thousandth of an inch).

 

The next challenge was to mount and calibrate the four sensors.  Although it's time consuming to use, a simple tabletop optical sensor has the lucky benefit of being the same sensor used 4 times, instead of 4 separate sensors.  Therefore the sensors need to be zeroed at the same surface.  Cyth had precision made granite blocks at several heights so that the sensors could be not only calibrated to the same block, but re-validated at any time if necessary.  Once the sensors are calibrated they all read the same for the gauge block.  For accuracy - the ability to return a known value with minimal error, this calibration was required.  Once calibrated the accuracy of the measurement had a standard deviation that rivaled the contact sensor machinists trust.

 

Keyence's advanced laser-based sensor products include single-point distance measurements as well as laser-line scanners for creating a profile.  Both product families include many measurement ranges and resolutions, laser color for different materials, and extremely high speed readings.  Cyth have successfully installed and validated Keyence products in numerous applications like these.

 

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