Summary: Contact measurement systems — CMMs, hard probe articulating arms, calipers, micrometers, roundness testers, contracers, gauge blocks, height gauges, and surface plates — are generally more accurate, with CMM tolerances ranging from 2–3 µm for entry-level devices down to 0.3 µm (0.0000118″) for the most advanced models. Non-contact systems use sensors that convert a physical property into an electrical signal without touching the object, collecting far more data far faster (some with refresh rates in the MHz range), but they are typically not as accurate — the most advanced models are within the single-digit micron range. Provided by KEYENCE.
Contact measurement systems are a group of measurement tools and devices most used for dimensional measurement. This includes coordinate measuring machines (CMMs), hard probe articulating arms, calipers, micrometers, roundness testers, contracers (contour measuring instruments), gauge blocks, height gauges, and surface plates.
CMMs tend to be some of the most advanced devices in the current market. They are computer-controlled and capable of measuring within very tight tolerances, ranging from 2–3 µm for entry-level devices down to 0.3 µm (0.0000118″) for the most advanced models.
CMMs are capable of dimensional measurements in three dimensions, but they are usually more expensive, space-consuming, and not as easily moved. In operation they tend to be time-consuming, because they navigate the inspected part from one point to another using a contact measurement sensor.
Other methods are less advanced and typically include manual tools such as calipers, gauge pins, gauge blocks, height gauges, and micrometers. These tools are only capable of measuring in one dimension, except for modern height gauges, which are capable of 2D and limited 3D measurements.
Contact measurement systems can measure a wide range of physical phenomena beyond dimensions, including vibration, runout, surface texture, flatness, and warpage. The choice ultimately depends on the physical property being measured and the nature of the sample or part being tested.
Non-contact measurement systems, also known as non-tactile measurement systems, rely on non-contact measurement sensors — devices that convert a physical property into a measurable electrical signal — to measure various physical phenomena without touching the object being measured.
These systems are particularly important in applications that involve delicate, soft, or extremely hot materials, where contact might damage the object or the sensor, or alter the measurements.
Measurable phenomena include surface roughness and texture, temperature, vibration and displacement, thickness, color and light properties, fluid flow and airspeed, electromagnetic fields, chemical composition, and dimensions and geometry.
The approach relies on transducer devices such as vision systems, laser scanners, structured light scanners, photogrammetry, and even CT scanners. Some systems rely on optical comparators — also known as profile projectors or shadowgraphs — which are now over a century old; while they don't produce a digital signal, their outputs can be digitized.
Besides making non-contact measurements, the main benefits relate to data collection: these systems collect and record a large amount of data while not making physical contact, and they gather more of the object's surface. Data collection happens very fast, and some systems feature a refresh rate in the MHz range, allowing capture of very complex shapes quickly — especially shapes with multiple axes or various physical features.
However, non-contact measurement systems aren't as accurate as contact measurement systems. The accuracy of the most advanced models on the market is typically within the single-digit micron range.
Contact measurements relying on tactile probes will typically be more accurate than non-contact methods. They are better suited for applications with high-precision requirements, especially where measurement tolerances are in the micron range. Internal measurements, such as hole diameters or slot width, might also require contact measurement.
Contact systems often provide simpler and more cost-effective solutions for more basic measurement tasks compared with more sophisticated non-contact systems. They are also notably less susceptible to environmental interference, which can affect the accuracy of non-contact measurements.
Non-contact systems excel at dimensional measurements and profiling of fragile, soft, or elastic material that would be easily damaged or deformed by tools.
They are best suited for applications that prioritize precise measurements of objects with complex geometries, as well as rapid measurements and large-volume inspections of dynamic or moving objects. This includes measuring properties of machinery in motion without affecting its operation, and rapid measurement and scanning of large volumes of manufactured parts, which is beneficial in mass production.
Real-time monitoring and feedback are among the most useful applications, as non-contact systems can detect defects in mass production, provide feedback, and trigger action in automated processes and control systems.
| Aspect | Contact | Non-contact |
|---|---|---|
| Accuracy | Higher; CMMs from 2–3 µm down to 0.3 µm (0.0000118″) | Typically within the single-digit micron range |
| Speed | Time-consuming; navigates point to point | Very fast; some systems refresh in the MHz range |
| Target suitability | Rigid parts; internal features such as hole diameters or slot width | Fragile, soft, elastic, or very hot materials; complex geometries; moving objects |
| Environmental sensitivity | Less susceptible to environmental interference | More susceptible to environmental interference |
| Cost | Often simpler and more cost-effective for basic tasks | More sophisticated systems |
There is no one-size-fits-all in measurement; sometimes a combination of tools is required.
Source: KEYENCE, "Contact vs. Non-Contact Measurement Systems" https://www.keyence.com/products/measure/resources/measurement-sensors-resources/contact-vs-non-contact-measurement-systems.jsp