Analog instruments are physical devices that use continuous signals (analog signals) to measure and display information. Examples of analog instruments include analog clocks, analog thermometers, analog voltmeters, and analog oscilloscopes. These instruments use dials, pointers, or needle movements to show information and do not use digital signals or display screens like digital instruments.
Analog instruments have been used for many years in various industries such as engineering, physics, and medical fields. They are known for their accuracy, reliability, and ease of use, which is why they are still used today even with the availability of digital instruments.
One of the key advantages of analog instruments is their simplicity. Analog instruments are often more straightforward to read, understand, and use than digital instruments. They also tend to have fewer components and simpler construction, making them less prone to failure and more durable.
Another advantage of analog instruments is their linearity. Analog signals are continuous and vary in a linear manner, which makes them well-suited for applications that require precise, accurate measurements. In contrast, digital signals are discrete and can only take on certain values, which can lead to errors in some applications.
All analog electrical indicating instruments require three essential devices:
(A) A DEFLECTING OR OPERATING DEVICE: A mechanical force is produced by the current or voltage that causes the pointer to deflect from its zero position.
(B) A CONTROLLING DEVICE: The controlling force acts in opposition to the deflecting force and ensures that the deflection shown on the meter is always the same for a given measured quantity. It also prevents the pointer from always going to the maximum deflection. There are two main types of control devices; spring control and gravity control.
(C) A DAMPING DEVICE: The damping force ensures that the pointer comes to rest in its final position quickly and without undue oscillation. There are three main types of damping used; eddy current damping, air-friction damping, and fluid friction damping.
There are basically two types of scale; linear and nonlinear. A linear scale is shown in Fig. 1(a), where the divisions or graduations are evenly spaced. The voltmeter shown has a range of 0–100 V, i.e. a full-scale deflection (fsd) of 100 V. A nonlinear scale is shown in Fig. 1(b) where the scale is cramped at the beginning and the graduations are uneven throughout the range. The ammeter shown has an fsd of 10 A.