What Is a Test Indicator?
A test indicator is a so-called lever-type dial gauge.
The measuring element at the tip moves up and down per displacement, amplifies the displacement using the principle of leverage, and the amount of displacement is converted into rotational movement of the needle to display the indicated value on a dial scale.
Depending on the shape and orientation of the display plate, there are standard, inclined, vertical, and horizontal types. There is also a universal type in which the dial scale can be oriented in any direction. The scale ranges from 0.01 mm to 0.001 mm per graduation, and the measuring ranges are large and small.
Uses of Test Indicators
Test indicators can be used not only for dimensional measurement but also for measuring flatness and parallelism by measuring several points on the plane of the object to be measured. It can also be attached to a machine tool’s spindle to measure the rotary axis’s runout. The runout value is used for various purposes, such as centering the rotary axis.
Test indicators are available from various manufacturers in terms of the direction of the scale plate, length of the measuring element, etc. This allows for the selection of optimum suitability for the application and situation.
Principle of Test Indicators
The test indicator has a built-in displacement amplification mechanism called a movement, a combination of gears inside the main frame. A measuring element attached to the movement is outside the main frame, and the measuring element moves up and down to measure the displacement.
The displacement of the measuring element is amplified in the movement using the principle of leverage. It is converted into the rotational movement of the needle through repeated amplification by a combination of gears. The amplification is so significant that displacement can be measured in increments of 0.001 mm. However, because of the substantial amplification, the range measured is as minimal as 1 to 2 mm, and the needle will swing beyond this range. Forcibly applying displacement while the needle is out of range can cause a malfunction.
The length of the measuring element must be adjusted according to the model and displacement. Therefore, if a combination not included in the manufacturer’s lineup is used, the accurate measurement value will not be displayed even if it is possible to install it successfully.