Properties of and working with dial gauges

Dial gauges are essential tools in industrial manufacturing and quality control. But how do you get the most out of them? In this blog, you will learn everything you need to know in order to make the best use of your dial gauges: from the most important features, to reading and clamping correctly, to avoiding measurement errors. You will also receive valuable tips on maintenance, care and calibration, so that your dial gauges work accurately for the long-term.

The most important properties of dial gauges

The main function of dial gauges is to record and display small length or position deviations. Due to the large number of applications in industrial practice, dial gauges must have a number of essential characteristics to meet requirements.

Measuring range and scale graduation

The measuring range of a dial gauge defines the maximum travel distance it can record. In industrial applications, this is often in the range from 0-10 mm and up to 100 mm or more. On the other hand, the scale graduation determines the reading precision. Typically, the dial graduation ranges from 0.01 mm to 0.001 mm on particularly accurate dial gauges. The measuring range and the scale graduation are important parameters because they reflect the ability of the dial gauge to accurately indicate even the smallest deviations.

Measurement accuracy and repeatability

The measurement accuracy describes how close the measurement result displayed by the dial gauge corresponds to the actual, true value of the object to be measured. It is a metric for how accurate the instrument is. The lower the difference between the measured value and the actual value, the higher the measurement accuracy. A high measurement accuracy means that the dial gauge is able to record the actual measurement of a component or a length as accurately as possible.

The repeatability, or reproducibility, refers to the ability of the dial gauge to always deliver the same measurement result when the same object is measured repeatedly under the same conditions. This means that the measuring device is able to measure consistently and reliably without any large deviations occurring between the individual measurements. A high repeatability means that the results do not differ or only differ minimally for multiple measurements of an object, even if the measurements are carried out at different times or by different operators.

It is possible that a dial gauge has high repeatability, but low measurement accuracy. In such a case, the dial gauge provides consistent but systematically false results. Conversely, a dial gauge could be very accurate, but have poor reproducibility, indicating that the results are inconsistent and vary greatly between measurements.

Robustness

In industrial environments, dial gauges must be robust enough to withstand harsh conditions. They should be resistant to shock, vibration, dust and humidity. Many dial gauges are therefore designed to be shock-proof and have different protection classes, which protect them against the ingress of dust or splash water, for example. Another aspect is the ability to secure the dial gauge in different positions in order to perform precise measurements even in difficult-to-access areas.

How are dial gauges correctly clamped in place?

The precise measurements of length deviations and tolerances contribute significantly toward ensuring product quality. However, working correctly with dial gauges is essential to guarantee this precision over the long term. Clamping dial gauges is an important step since even the slightest movements or vibrations can falsify the measurement result. In industrial manufacturing and metrology, dial gauges must be secure such that they are stable and accurately positioned to provide reliable measurement results.

• Magnetic measuring stands: Magnetic measurement stands are one of the most common methods of securing dial gauges in a reliable and flexible manner. These stands consist of a robust base equipped with a strong magnet and a flexible adjustment arm. The magnet ensures a strong bond to metallic surfaces. The arm can be adjusted at different angles and heights so that the dial gauge can be precisely placed in the desired position.
• Stands with clamping devices: In addition to magnetic stands, there are mechanical stands with clamping devices that can be attached to workbenches, machines or specialized brackets. These mechanical clamping devices hold the dial gauge securely and prevent any movement or vibration.
• Measuring tables and measuring stands: Measuring tables or measuring stands are often used for very precise measurements in laboratories or for highly-accurate industrial measurements. These devices offer high stability and precise adjustment options to precisely align dial gauges.
• Measurement gantries and specialized fixtures: Specially manufactured fixtures, such as measurement gantries or special-purpose fixtures, can be used in certain applications, especially for mass production or automated measuring processes. These systems are customized for the respective measuring task and ensure accurate and repeatable positioning of the dial gauge.

How are dial gauges read correctly?

Reading dial gauges correctly is a key requirement for accurately determining dimensional deviations and ensuring product quality in industrial production. Even small errors during reading can lead to incorrect measurement results and thus to rejects or faulty components. Positioning or aligning the dial gauge is a first essential step. On analog and digital dial gauges alike, the measuring tip must contact the surface to be measured exactly vertically. Correct vertical alignment prevents deviations and ensures precise measurement results.

The measurand is read on analog gauges by interpreting the dial position on the scale. The correct reading technique requires an understanding the scale graduation. At a usual graduation of 0.01 mm, the dial moves one full rotation for 1 mm. More precise graduations, such as 0.001 mm, are shown by smaller distances, and some dial gauges have an additional decade scale for easier readings of several millimeters. Digital dial gauges display the measurand directly on the display, thus minimizing reading errors. In addition, many models offer the option to switch between millimeters and inches, and the correct unit of measure should of course be set before the measurement.

Interpreting the measurement result correctly is an important step in addition to precise measurement. The measurands should always be compared against the specified values, the specified tolerances should be taken into account, and possible temperature and environmental influences should be included in the assessment.

Measurement errors and how to avoid them

There are several typical error sources when using dial gauges that should be avoided:

• Inaccurate zero position: An inaccurate zero position will result in systematic deviations. Before each measurement, the operator must verify that the dial gauge is zeroed correctly.
• Incorrect contact pressure: The pressure with which the measuring tip makes contact against the workpiece can falsify the measurement. It is important to maintain the correct contact pressure in order to obtain exact measurements.
• Incorrect dial gauge alignment: The dial gauge must be aligned exactly perpendicular in relation to the measured object. Even slight angular deviations can falsify the measurement.
• Contamination: The surface to be measured should be clean and free of dust, oil or other contaminants since such contaminants could falsify the measurement.
• Temperature fluctuations: Particularly for precision measurements, the workpiece should be brought to the same temperature as the dial gauge in order to avoid thermal expansions.

Accuracy and calibration of dial gauges

Dial gauges consist of mechanical or electronic components that exhibit signs of wear over time due to use or environmental influences such as temperature fluctuations, humidity or vibrations. This can lead to deviations in the measurement accuracy. An uncalibrated dial gauge can therefore provide faulty readings, which in turn can lead to quality problems, rejects, or rework. However, dial gauges must be able to reliably and reproducibly record the smallest deviations. Regular calibration is therefore of decisive importance to ensure that dial gauges also provide precise measurements over the long term.

Calibration intervals

The calibration must be carried out at regular intervals as part of the monitoring test to ensure the precision of the dial gauges. The calibration intervals depend, among other things, on the frequency of use and the operating conditions. The more often a dial gauge is in use and the more demanding the environmental conditions are, the more often a dial gauge should be calibrated. With regard to calibration intervals, the basic principles and latest instructions for inspection equipment monitoring as well as the recommendations and specifications of the gauge manufacturer must always be observed.

Influence of the calibration on the measurement

Calibration directly influences the measurement as it minimizes systematic measurement errors and measurement deviations. Without regular calibration, inaccurate measurements can lead to misinterpretations, and this in turn can compromise the quality and safety of products. The calibration ensures that the measuring instrument measures correctly, which is particularly critical for avoiding systematic errors.

Gauge blocks for calibrating dial gauges

Industrial metrology relies on gauge blocks as standardized, rectangular blocks that have extremely precise dimensions and are used for calibrating and testing measuring instruments.

They are available in various sizes and allow precise length measurements to be performed in the micrometer range. Gauge blocks are generally made of steel, ceramic or tungsten carbide and are ground and lapped to extremely high accuracy. They have two exactly parallel surfaces, the spacing of which corresponds exactly to the imprinted nominal length. The main task of gauge blocks during calibration is to provide an exact and reliable reference for length measurement.