Image Credit: Fischer Technology | Control Company | Thorlabs

Dimensional gages and instruments provide quantitative measurements of dimensional and form attributes such as wall thickness, depth, height, length, inner diameter (ID), outer diameter (OD), taper and bore.

Types of Dimensional Gages and Instruments

There are many types of dimensional gages and instruments.
 

• Gage blocks or master gages are used to calibrate, check, or set variable or fixed limit gages. Gage systems or stations are large, complex units that are typically available in bench top or floor mounted configurations.
• Go/no-go, functional, and attribute gages are precision tools for comparative gaging based on fixed limits.
• Indicators and comparators include a precision spindle whose linear movements are amplified and displayed on a dial or digital display.
• Dimensional gages and instruments include specialized devices that measure thickness, thread size, pitch, serration, and other parameters.
• Height gages include micrometer, laser micrometer, and micrometer head gages.

Gage Technologies

There are several gaging technologies for dimensional gages and instruments.

• Pneumatic gages use air nozzles or inlets to control airflow and pressure. Pneumatic comparators, digital readouts, and analog amplifiers are used to display air gaging dimensional data.
• Electronic gages use linear variable differential transformers (LVDTs), capacitance, and inductive or other electronic probes to sense the distance or displacement of a contact or stylus.
• Mechanical gages rely upon the physical movement or displacement of a gaging element such as a spindle, slide, or stem to determine a part’s dimensions.
• Micrometers, calipers, indicators, plug gages, and ring gages are examples of mechanical gages.
• Dimensional gages and instruments that use optical, laser, or video-based technology are also available. 

Specifications

Selecting dimensional gages and instruments requires an analysis of variables such as part or component geometry, production volume, gaging conditions, and dimensional tolerance requirements.

Important specifications for dimensional gages and instruments include range and resolution.

Some dimensional gages and instruments display measurements according to the English or imperial system. Others devices display metric amounts. 

Features

Optional features include National Institute of Standards and Technology (NIST) traceability, gage calibration, and tool setting capabilities.

• Vernier graduated scales display dimensions to an intermediate level such as tenths.
• Automatic devices that provide statistical variation or process control parameters based on dimensional data often include a personal computer (PC) interface and statistical process control (SPC) software.
• Portable and handheld dimensional gages and instruments can be used for field work.  
• Additional mounting options include benchtop, table-based, or floor-mounted. Test indicators, dial indicators, and micrometer heads are typically machine-mounted.

Display Options

Dimensional gages and instruments are available with many different types of displays.

• Analog devices use a pointer or needle mounted in a disc dial.
• Digital devices present data in numeric or alphanumeric form and often feature data output capabilities that use serial or other formats.

• Column and bargraph displays provide a way to present dimensional data graphically.

• Remote displays are used with electronic and optical gages, probes, and gage heads that lack an integral display and are used in production or hazardous environments.

Standards

Dimensional gages and instruments must adhere to certain standards to ensure proper design and functionality.

MIL-G-13451 - This specification covers procurement requirements for gages and gage cases.

ASME B89.1.13 - This Standard is intended to provide the essential requirements for micrometers as a basis for mutual understanding between manufacturers and consumers. Outside, inside, and depth micrometers are described in the Standard. 

DIN EN ISO 3611 - This International Standard specifies the most important design and metrological characteristics of micrometers for external measurements: