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Key Differences in Dimensional Measurement Systems

When performing dimensional inspection, there are many measurement methods which are very accurate and highly recommended. In this article, our experts will explain some of the benefits and key differences between some of those methods including: CMMs, portable measuring arms, vision systems, and optical comparators.

Coordinate Measuring Machines or (CMMs):

CMMs have been used for years in the quality industry. As many quality labs are required to perform precise measurements on several detailed items at a time, CMMs have been the “go to” form of measurement in quality labs. One of the biggest benefits of using a CMM in your quality lab is the ability to write programs which can be run automatically without the constant monitoring of an operator or expensive custom designed fixturing.

CMMs are designed to take measurements in three dimensional space and can make use of your 3D CAD model providing a comparative measurement to the perfect part. Because of this setup, most CMMs are fully customizable based on your application and can range from $100K to $500K. A CMM is the best option for in lab measurements that require 3D analysis or large volume measurements.

Portable Arm CMM's:

Portable measuring arms are similar to CMMs, however since they are mobile with a greater range of motion, they are primarily used for taking large measurements of items while in production. Since a CMM’s range is restricted to the surface area of its table and the height of its bridge, a portable measuring arm may be the best solution for measuring very large parts or those still in the manufacturing environment.

As with CMMs, portable measuring arms require trained operators, but give you greater capability than other methods of measurement with powerful software. Portable measuring arms are typically a good option for production operations with large parts that need measurement without disrupting processes.

Optical Comparators:

Optical comparators, like CMMs, have been used for many years to take two dimensional measurements of objects projected onto a glass screen. Because of projection methods, optical comparators can make small items measurable with relatively simple internal components. Older and less expensive optical comparators work by manually taking measurement points with crosshairs on the screen. Some newer models feature an edge detection which automatically records a point when crossing a plane to improve accuracy. LED lighting has greatly improved the contrast and reliability of the optical system.

Optical comparators have expanded over the last 5 years to include fully automated measurement as well as comparative measurements to your CAD model. These are typically a good option in production environments with spot checks on simple parts.

Key Differences in Dimensional Measurement Systems 1
OGP Focus Optical Comparator

Vision Systems or Video Measurement Systems:

With advances in technology and the increasingly fast paced environments in many industries, vision systems have entered the market to improve speed and efficiency. Before vision systems, quality labs have had to rely on slower forms of measurement such as optical comparators or the unnecessary power of a CMM. A vision system ties that all together in a much faster tool utilizing a camera, touch trigger, and laser sensors in one platform that can measure 3D parts. Part sizes can range from .05” to 36” depending on the platform.

Like CMMs, most vision systems are fully customizable based on your application. They come with a variety of sizes and field of view options based on needs. The software used on most of these systems is very user intuitive and easy to use. These systems are highly accurate and offer the most versatility when tackling tough measurements.

Key Differences in Dimensional Measurement Systems 2
OGS SNAP 350 Large Field of View Systen

The Key Differences:

While CMMs are great for detailed three dimensional objects, portable measuring arms are needed for production floor measuring of larger parts, Vision/Multi-Sensor systems are versatile and fast. Optical comparators are much quicker at taking two dimensional measurements and are the easiest to use. Take a look at the table below to check out some general comparisons to see which method might be best for your application.

Coordinate Measuring Machine (CMM)Portable Measuring ArmVideo Measurement SystemOptical Comparator
Trained/Certified Operator Required?YesYesDepends on SoftwareNo
Customizable System?YesYesYesYes
Dimensional Capability3D3D3D/2D2D
Contact Measurement?YesYesOptionalNo
AccuraciesTypically 0.0002″Typically 0.001”Typically 0.0001”Typically 0.0002”
Compatible with CAD/DXF?YesYesYesNo
Environmental RequirementsLab or Clean Room – 68° FIn Lab / Shop FloorIn Lab / Shop FloorIn Lab / Shop Floor
Space RequiredFloor Standing:25-50 sqftMobile Unit: 3-5 sqftTabletop: 5-10 sqftTabletop or Floor Standing: 5-10 sqft
Air Required75-80 PSINoNoNo
Suggested Use:Use in lab for repetitive or 3D measurements of detailed partUse for large machined parts in line on production floorUse in lab for quick and simple repetitive 2D measurementsUse in lab for quick and simple 2D measurements
Price Range$50K-$500K$50K-$125K$25K-$250K$15K-$60K

Still unsure of what would be best for your operation? Give us a call to learn more or fill out our contact form to request information about equipment! Let us help you select the correct equipment for your needs.

See how our precision measurement team can help improve quality, increase efficiency, and reduce risk.

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In the meantime, enjoy these fun facts…

Did you know... the precision measurement group at Cross was founded in 1939 by our current CEO's grandfather, Jim King. That's a whole lot of calibration!
Did you know... A fingerprint weighs about 50 micrograms. We know, we weighed it! The residue left from a finger can actually make a difference in weight results which is why we wear gloves when we calibrate weights. For reference, a sheet to paper is about 4.5 grams, that’s 4.5 million micrograms.
Did you know… Cross Company is an ESOP (Employee Stock Ownership Plan). Our ESOP started in 1979 and as of 2006, we are a 100% employee owned! Learn more about our ESOP and how that benefits both team members and our customers.
Did you know… Cross Company has grown significantly since our start in 1954. Over the years we've acquired 26 companies! Today, our five groups have expertise in everything from industrial automation to precision measurement, and industry knowledge going all the way back to 1939.