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What does “dial reading” mean? Why are there different types of dial readings?

The heart of a dial indicator is the dial reading that it provides as a measurement. Dial indicators measure the deviation of the readout of an object from the expected readout. A very precise tool, the dial indicator is particularly good at identifying differences in measurements that are difficult to discern using the human eye alone. In other words, the dial reading seen on a dial indicator indicates the differences between expected and actual measurements of a part. There are a number of different types of dial indicator readings. Each type is similar in that it retains the clock-like structure expected, but different in the type of information that is displayed, in size, and in connection method.

Two overarching categories of dial indicator are balanced and continuous. On a balanced dial indicator, the dial reading runs in two opposing directions away from the zero point in the center. These are typically used when the tolerances of a measurement are bilateral, for example ±0.002 inch, because the dial is similarly balanced in either direction. Commonly, the positive numbers will begin on the right while the negative numbers begin on the left of the zero midpoint. Continuous dial indicators, alternatively, do not have numbers running in both directions, but instead only have a continuous number set running from the zero point all the way around the dial and back to the zero point. These dial indicators are mostly used for tolerances that are unilateral, for example –0.000 to +0.004 inch. Both the balanced dial indicators and continuous dial indicators come with reversed versions. These dial readouts are exactly the same as described above, but backwards. For this reason, the reversed continuous dial indicators are sometimes referred to as counter-clockwise indicators.

Beyond the basic balanced and continuous designs seen on dial indicator readouts, there are three other types of dial indicators that are worth mentioning. Test dial indicators, sometimes known as lever arm test indicators or finger indicators, are typically used for measuring angular displacement as opposed to linear displacement. This device comes with an extended arm on one side that is movable on its hinge, thus the movement of the arm indicates displacement. Plunger dial indicators look similar to the other types, but include a mounted plunger which acts as the measuring device by determining the degree of linear thrust. The plunger dial indicators are common for measuring both mechanical and electrical designs, for example injection molding machines. Finally, lever dial indicators utilize a scroll mechanism and a lever mechanism in order to move the stylus around the dial and measure displacement. A benefit of lever dial indicators is their small size. More generally, dial indicators can also vary based on how they connect to what they are measuring. The two options most commonly seen is a swivel clamp or a c-clamp. The choice between these two clamps depends on the shape and size of the machine or part being measured, and does not impact the type of dial reading.

When it comes to the measuring range of a dial reading on a dial indicator, some indicators use what is a called a one-rev measuring system. This stands for one revolution and signifies that the dial has a limited range of only revolving around the face of the dial once. One-rev dial indicators are excellent for measurements that require a high level of detail or magnification. They work to eliminate any chance of error in counting the revolutions and final resting place of the dial hand. Other dial indicators can move up to ten whole revolutions. These measurements involve the sum of different readout ranges.

Dial indicators help amplify small distances of deviation for easier measurement and do so through various types of dial readings. The dial reading itself is at the center of how these wonderful tools work.


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