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Amplifier Types

There are many different types of amplifiers. The first type to be discussed is operational amplifiers. These are also known as op-amps. Op-amps are integrated circuits where the chip contains the transistors of the stages and resistors and capacitors as well. An op-amp is a differential amplifier on a chip, in which most points in the circuit are accessible through terminal connections. The terminals can be linked, so different parts or all of the differential amplifier can be used for different functions. Since both stages of the differential amplifier produce opposite outputs, either stage can be used as an inverting or noninverting amplifier. Since the first stage feeds the second stage as an emitter follower, the emitter follower output can be used.  It can be used with one or two inputs, or one or two differential or emitter-follower outputs. If external resistors for feedback or stabilization are added, the op-amp can also function as oscillators, gates, counters, and various others. Op-amps are used extensively in digital meters.

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Test Equipment Display Types

Displaying readings on an analog scale, where the digital characters are printed on the scale in the different locations that the pointer swings is not an issue. But, putting digits on a digital readout where different digits must share the same location, is more difficult. Three ways have been used: the solid character, the dot matrix, and the bar segments. The solid character can be the most pleasing way of displaying digits, but it is problematic since they must all share the same space. This was the way the servo wheels worked, and electrically, it was done with Nixie tubes. These used ten transparent in-line wafers enclosed in neon gas. Each wafer had electrodes in the shape of numerals, which glowed when the wafer was electrified. Although the unused wafers were still discernible while one wafer glowed, it was tolerable. The Nixie tube was used for years and can still be found on special equipment. However, this method is costly and the tubes are fragile.

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Passive Voltage Probe Measurements

One of the probe types that can be used with an oscilloscope is a passive-voltage probe. The simplest passive-voltage probe is a coaxial cable. But what happens when a coaxial cable is linked to the device under test? A schematic diagram of the test arrangement is given in Fig. 4.1. The device under test is symbolized as a signal source with an internal source resistance Rs.

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Fiber Optics

Fiber optics use hair-like glass fibers to cany modulated light to transmit signals over distances. Light signal systems use simpler equipment, less energy, and are less prone to interference. The glass fiber has a clear core to carry the light and a cladding that is highly reflective, as well as a protective coating. Light beamed into the core is reflected from side to side to keep it moving down the core. An electronic signal, such as a telephone signal, is converted to a light beam by a light generator, which can be a light-emitting diode (LED) or a laser diode. The light is transmitted down the fiber through various optical connectors, jumpers, patch panels, etc., and is picked up at the receiving end by a photodetector that converts it back to an electronic signal. Long cable runs use weld-like splices. Clear optical continuity is needed for light transmission.

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Insulation and Dielectric Testers

A dielectric is an insulating material, but it is an insulating material that has been manufactured with certain electrical characteristics to interact with other electrical characteristics of a component to give the component its ratings. The insulating material between the plates of a capacitor is a dielectric. It helps determine the capacitance value and must resist voltage breakdown at the rated voltage of the capacitor.

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