Measurement testing is critical to quality assurance. Advances in metrological science make measurement more precise than ever before. Industries from aeronautics to medical engineering have raised the bar, demanding the latest in ultra-precise measurement technology.
Don't get left behind. Bring the best in dimensional measurement tools to your organization.
Not sure where to start? Read this brief guide to must-have dimensional measurement instruments. Learn how metrology works, how standards are set, and the types of tools that can elevate manufacturing precision.
Length and Dimensional Measurement: Overview
Length and dimensional measurement is a way to determine the metrics of an object. Specifically, it quantifies an object's:
- Physical size
- Characteristics of shape and form
- The distances among the object's components
Physical size quantities can be height, depth, or thickness. Characteristics may be the object's roundness, flatness, or shapeliness. Distances may include the degree of angles or the length between nodes.
International System of Units (SI)
SI is the international standard of measurement units. Informally, this is the metric system.
The General Conference on Weights and Measures created and maintains the SI standard. Standards are derived from universal constants. The Consultive Committee for Units (CCU) conducts metrology experiments to develop and codify new standards.
ISO Geometrical Product Specifications
In 2012, the International Standards Organization (ISO) published the geometrical product specifications handbook. This book sets industry standards for planes and three-dimensional, manufactured products. The handbook includes standards for:
ISO has also published guides articulating each of these standards separately, in greater depth. ISO also sets standards for metrology tools.
For example, you may use micrometer to measure height. Before use, you may consult the ISO guide to height-setting and micrometers.
ASME Codes and Standards
The American Society of Mechanical Engineers (ASME) is another relevant standard-setting organization. It's critical to stay aware of ASME standards when you choose metrology tools.
Consider AMSE's codes and best practices for dimensioning & tolerancing. These codes standardize symbols on engineering drawings and data models you'd use to create geometric objects. With these codes, you can maintain accuracy per product specifications.
National Metrology Centre Standards
The National Metrology Center (NMC) is a Singapore-based measurement research center. NMC categorizes precision measurement systems by process and utility. Metrologists using NMC classification identify five types of dimensional measurement tools:
- Laser frequency measurement
- Linear dimensional measurement
- Angle measurement
- Form measurement
- Complex geometry metrics
NMC publishes category summaries on its official site. Explore the category summaries to understand categorization in greater detail.
Must-Have Dimensional Measurement Tools
Now you're familiar with international metrology standards and categories. With that knowledge, you're ready to examine some of the most common and effective dimensional measurement tools available. Which tool/s best fit the specific feature and function of your application?
Micrometers are gauges that measure precision diameters, lengths, and/or thicknesses. Industrial professionals use a wide variation of micrometers, but the most common include these seven distinct types that correspond specifically to a given application:
- External micrometers
- Internal micrometers
- Bore micrometers
- Height micrometers
- Laser micrometers
- Jig borer micrometers
- Thread micrometers
Jig borer micrometers are built into microscopes, telescopes, and medical equipment. In contrast, external and internal micrometers are independent tools that determine the dimensions of a cavity. Engineers develop thread micrometers with unique elements to improve their measurement of pitch and thread size.
In 2021, engineers developed new, high-precision wire micrometers. These tools can measure the diameter of any wires and fibers less than 50 mm wide. The new micrometers' accuracy is granted under two nanometers' uncertainty.
Digital Calipers With Automated Data Transmission
Calipers are one of the oldest dimensional measurement tools. They measure the distance between opposing sides of an object. Calipers may also determine internal and external distances. Digital calipers improve measurement by reducing human error. The newest digital calipers are enabled with Wi-Fi, which automatically transmits measurement data to a variety of devices such as PC's, cell phones, and iPad's. This allows information to be exported to a variety of platforms from Microsoft Excel to Statistical Processing Control software.
Traditionally one of the most efficient ways to perform highly accurate non-contact measurements on small parts. Optical comparators have been a longstanding mainstay for manufacturers of precision parts due to their rugged construction, large viewing screen, and ease of use. The size and features of a part will determine comparator specific requirements such as lens magnification, viewing screen size, table size and capacity, as well as the functions of its digital readout.
In recent years comparator manufactures have begun to replace traditional magnification lenses with camera based lenses. This change has transformed the conventional optical comparator into an vision-based digital measurement system. The technology allows for a multitude advantages including an increase in speed and accuracy with increased magnification ranges, automated part measurement, and the capability to import digital overlay's.
An air gauge is a pneumatic gauge. It can determine internal volume and form. Air gauges can perform a roundness assessment with a high degree of accuracy. This holds regardless of the shape of the slot of the cavity it measures. Metrology professionals use air gauges to develop master measurement systems. A core function of these systems is internal diameter measurement. Air gauges can also determine the cylindricity of an object.
Coordinate Measuring Machine (CMM)
Coordinate measuring machines are widely used contact based inspection tools in manufacturing. CMMs incorporate four elements:
- Machine structure components
- Linear measurement transducers
- Probe systems
- Computer hardware and software
The NIST reports on technological advances relating to each of those elements. Improvements to any part increases CMM precision.
Recent developments in optical coordinate technology and video probes, for example, have improved measurement accuracy. Some of the improvements enable accurate CMM assessments in illuminated environments. This builds on previous improvements to sensor equipment.
Vision-Based Measuring Systems
Vision-based measuring systems are useful metrological tools. Contemporary systems use an array of linked capacitors to transfer electric charges. This, in turn, generates digital images.
Advances in these CCD arrays have increased the accuracy of measurements of mean deflected shapes. Engineers use these tools to monitor structural deformations.
In 2012, engineers developed a comprehensive system to measure and characterize polymer forms. This system uses micro-CT and x-ray technology. These developments move polymer metrology forward.
Height Measurement Tools
Height measurement tools are critical pieces of dimensional measurement equipment. While there's a vast array of height measurement technology, there are three types oft-used in international industries. Consider one of the following tools for your practice.
Vernier Height Gauge
A vernier height gauge measures vertical distances. manufacturers also use these gauges to measure the flatness of granite surfaces and the angular offset of a datum plane. The great benefit of a vernier height gauge is its capacity to take both internal and external measurements.
Inclinometers determine the orientation of an angle of an object. Inclinometer calculations take gravity as an independent variable. This gravity relation calculation makes inclinometers useful tools to measure:
- the angle of Earth's magnetic field on diverse horizons
- the list of a ship
- the strike and dip of geological features
- the range of motion of joints
- the optimal solar panel placement
Some engineers call the industrial inclinometer a "tilt sensor." It typically uses microelectromechanical systems technology (MEMS) to run its sensor. A dynamic inclinometer utilizes a 3D acceleration sensor and a 3D gyroscope.
Laser hypsometers measure the full distance from the top to the bottom of an object. Hypsometers may be applied in topography, forestry, and architecture. Ultrasonic hypsometers use sound waves to measure the height of a distant object.
Contour Measurement System
A contour measurement system determines the curvature, flatness, or roughness of a plane. Contour measurement tools determine:
- Coordinates of a workpiece
These metrics characterize the contours of an object. Some contour measurement tools use these metrics to generate a surface profile or map of the object.
Short-Range Laser Displacement Contour Tool
This tool uses laser displacement to generate a topographical map of a surface's contours. It may utilize a 3-axis motion sensor. A sensor's position on the z-axis is stable. Then, the feedback distance from the sensor position to the surface informs the contour map.
Contracers utilize traceable angles to determine the value of contours in a piece. These tools are useful for high-volume measurement of surface contours at scale. The contracer is the standard tool to measure the contours of automated brake components.
Optical Surface Technology
Engineers have used advances in optical technology to improve precision surface topography measurement. In 2019, engineers proposed a traceable standard for measuring the contours of transparent surfaces.
This standard uses contour measurement tools derived from four distinct optical technologies. The technologies are:
- Photoacoustic Imaging (PAI)
- Fiber Optic Video Measurement (FVM)
- Coherence Scanning interferometer (CSI)
- Imaging Confocal Microscopy (ICM)
These technologies fuel the latest tools for clear surface topography.
Error Compensation System: Modelling, Sensing, Tracking
Error compensation tools are a line of defense against errors in primary measurement tools.
Real-Time Error Compensation (RTEC) is a method of accuracy enhancement. These systems act as a safety net. They catch potential metrical inaccuracies using error modeling techniques.
Many error compensation systems use laser and proximity sensors to track errors. The sensor transmits data wirelessly. The system then computes the data. Engineers develop diverse sensor network strategies to facilitate compensation.
Static vs. Dynamic Error Modelling
Error compensation systems use either static or dynamic error modeling. One 2010 experiment explored a method of dynamic error modeling for five-axis high-speed machining. Machinists can apply the data from this experiment to develop (or purchase) an effective systemic error compensation tool.
Error Compensation for Machining Tools
In 2004, engineers applied an RTEC technique to NC machinery. The resulting tools compensated for geometric-thermal errors. NC machinery processes can be prone to heat-based errors.
Parametric error compensation enhances the dimensional accuracy of micro-features with miniaturized tools. Parametric error compensation tools use kinematic models of micro-machines. They then analyze data with computational geometry.
In 2010, engineers found that microfeatures had better dimensional accuracy after they applied parametric error compensation. Other tools provide:
- Volumetric error compensation
- Misalignment error compensation
- Static deflection error compensation
- Spindle growth error compensation
These errors are common to CNC machinery.
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