Measuring Technology – Quality Control Through Measuring Methods

In industrial manufacturing, measurement technology is a fundamental component for monitoring and quality control. Industrial measuring techniques allow collecting and quantifying precise data and information about the sizes, properties and characteristics of objects. The following article discusses the importance measurement technology has for quality assurance, and it introduces some methods from measurement technology.

Importance of Measuring Techniques in Quality Assurance and Quality Control

Measurement technology refers to the systematic use of measuring instruments, measuring methods and measuring processes for the recording and analyzing identifiable variables quantitatively.

These can be, for example, physical variables, properties of objects and substances, as well as processes or systems. One possible focus for the use of measurement technology is the verification of product standards and specifications. Defects and deviations can thus be detected and corrected in a timely manner, even before the products come onto the market.

The following advantages result from the utilization of different measuring techniques:

• Ensuring product quality: Measuring techniques are used to quantify the properties and characteristics of products and to compare them with the underlying requirements (e.g., standards or customer requirements). This means that defects and deviations are detected in good time and preventive actions can be initiated. This reduces the costs for reworking.
• Process control and process optimization: Measuring techniques enable continuous monitoring of production processes. Deviations can be detected in real time and corrected by early intervention.
• Data-driven decision-making: The data supplied is precise and reliable. For example, they can serve as a basis for process improvements and design changes and support decision-making.
• Traceability and documentation: In general, measurements are documented for seamless traceability. This approach is particularly beneficial in highly regulated industries.
• Continuous improvement: Thanks to the analysis of measurement data, improvement processes can be developed continuously and implemented.

DIN 1319 for Measurement Technology

The basic standard for measurement technology in Germany is DIN 1319. It defines the following:

• Part 1: Basic Terminology (1/1995)
• Part 2: Terminology Related to Measuring Equipment (10/2005)
• Part 3: Evaluation of Measurements of a Single Measure; Measurement Uncertainty (5/1996)
• Part 4: Evaluation of Measurements; Measurement Uncertainty (2/1999)

The Parts of the Standard define, among other things, terms for measuring equipment, evaluation and measurement uncertainty. This includes the following means:

• Measuring devices
• Measuring equipment
• Standard
• aids
• Reference materials
• Devices for calibration or adjustment

Software is one of these tools. It is used, for example, to perform measurements using CAD models of test specimens. To ensure quality, test equipment must be monitored at regular intervals.

Measurable Variables

The following table provides an exemplary overview of measurable variables and suitable measuring devices:

Industrial Measurement Technology

For precise measurements and quality controls, there are different types of measuring techniques, both mechanical and non-contact:

• Mechanical measurement technology, for example measuring length with rulers, calipers or micrometers, measuring angles with goniometers or angle measuring devices
• Electrical measurement technology, for example measuring voltage with voltmeters or measuring currents with ammeters.
• Optical measurement technology, for example cameras
• Temperature measurement technology, for example thermometers

Some of the measuring techniques and their application possibilities in the industry are discussed in more detail below.

Mechanical and Tactile Measuring Techniques

Mechanical measuring instruments are used in various applications and industries to measure lengths, angles, pressure, temperature and other physical parameters. MISUMI offers a wide range of mechanical measuring techniques, for example:

• Inner diameter measuring tools
• Gauges
• Calipers

Tactile measuring techniques are a sub-area of mechanical measurement techniques. Tactile measuring sensors such as styluses or tactile probes can be used to measure lengths, widths and heights of components or workpieces. These are often used in manufacturing to ensure that parts have the correct dimensions.

Electrical Measurement Technology

In electrical measurement technology, electrical values such as voltage, amperage, resistance, power and other electrical parameters are primarily measured. An electrical measurement can, for example, proceed as follows: First, a sufficiently dimensioned measuring device must be selected. The measuring leads of the measuring device are then connected to the circuit to be tested or the device to be tested. To avoid short circuits, measuring tips should not come in contact with other parts of the circuit. In digital devices, the indicator may have to be calibrated to zero before the measurement. The result obtained is then compared with the expected voltages and evaluated to determine whether it is within the normal range.

Optical Measurement Technology

Optical measuring techniques include, for example, industrial cameras that are directed toward the test object and are connected via a PC. The camera takes high-resolution images based on which parameters such as diameter are then calculated on the PC. The resolution extends down to the micrometer range. Optical measuring techniques are very flexible. They are suitable for a wide variety of workpieces. The principle works via the shadow edges of the objects: everything that can be depicted in the shadow can be measured using optical measurement technology. Nevertheless, the optical measurement technology has its limits: Special features such as grooves, bore holes or gear teeth in shafts cannot be reproduced this way. In these cases, it is advisable to add tactile measuring techniques to the optical measuring techniques. A measurement probe can, for example, scan and measure a gear.

Acoustic Measurement Technology

Acoustic measuring techniques use various parameters such as the travel time of ultrasonic waves or reflection patterns to identify defects, irregularities or material changes. They are completely non-destructive. Ultrasonic sensors, for example, work with the propagation and reflection of sound waves. The sensor is held on one side of the workpiece, the contact surface area may be enlarged via a coupling agent such as a gel, and then the sound waves are guided into the workpiece. At the other end, they are reflected either by an attached stopper or also without one and sent back to the starting point. The transmitter then becomes the receiver. If there are now cavities in the workpiece, these would send back the reflection echo much earlier and be recorded as so-called error echo in the evaluation. Ultrasonic sensors can also be used in difficult-to-reach locations, such as bore holes.

3D Measuring Technology

In 3D measuring technology, precise three-dimensional measurements of objects are carried out. It allows collecting data about the geometric features and the spatial structure of three-dimensional objects. The 3D measurement technology can comprise various techniques such as laser scanning, fringe projection, stereovision, coordinate measuring machines (CMMs) and many others.

A coordinate measuring device works, for example, as follows: A CAD model of the workpiece to be tested is created and entered into a special software. The workpiece is then placed in the coordinate measuring device and its position is transferred to the software by means of pre-measurements. The device then traces the contours on the real workpiece using the CAD model and passes this information directly to the software. There, the actual dimensions are directly compared with the required dimensions. Any deviations found, such as tolerance exceedances, are also directly marked at this point. A prerequisite for 3D measurement technology is, of course, a well-prepared CAD model.

Digitalization of Measurement Technology

In recent years, digitalization of measurement technology has made considerable progress. This has improved efficiency, accuracy and flexibility and enabled integration into sophisticated automated manufacturing environments.

Digitalization has the following advantages:

• Networking and Integration: Measurement technology is increasingly integrated into networked systems and Industrie-4.0 environments. This enables the transmission of measurement data via the Internet of Things (IoT) and the seamless integration of measurement technology into production processes.
• Data processing and analysis: by recording measurement data digitally, highly complex calculations and statistical evaluations can be more easily created and used for well-informed decisions.
• Automation: Measurement processes can be automated (e.g. measuring devices are automatically controlled).
• 3D and image processing: More complex 3D models and surface analyses are possible.
• Remote monitoring and remote control: Measurements can be performed remotely, which is particularly useful in dangerous or environments that are difficult to access.