Basic Controls of a CRO

Number of controls are required to be provided on a panel of CRO to facilitate its proper functioning. Intensity control is provided for adjustment of brightness of the spot on the screen. It is accomplished by varying the voltage between the first and second anodes. The horizontal and vertical position controls are provided for moving the beam on any part of the screen. It is accomplished by applying a dc voltage to horizontal or vertical deflection plates. Similarly there are other numerous controls in a CRO, which will be discussed, in detail, here. Vertical Deflection System. The function of vertical…

Read More

CRT-Cathode Ray Tube

Cathode ray tube essentially consists of an electron gun for producing a stream of electrons, focusing and accelerating anodes for producing a narrow and sharply focused electron beam, horizontal and vertical deflection plates for controlling the beam path and an evacuated glass envelope with phosphorescent screen giving bright spot when struck by a high velocity electron beam. A cutaway view of an early CRT is shown in figure. CRT-Cathode Ray Tube Electron Gun Assembly. The electron gun assembly consists of an indirectly heated cathode, a control grid surrounding the cathode, a focusing anode and an accel­erating anode. The sole function…

Read More

CRO-Cathode Ray Oscilloscope

Introduction to CRO – Cathode Ray Oscilloscope The cathode ray oscilloscope is an extremely useful and versatile laboratory instrument used for studying wave shapes of alternating currents and voltages as well as for meas­urement of voltage, current, power and frequency, in fact, almost any quantity that involves amplitude and waveform. It allows the user to see the amplitude of electrical signals as a function of time on the screen. It is widely used for trouble shooting radio and TV receivers as well as laboratory work involving research and” design. It can also be employed for studying the wave shape of…

Read More

Q-Meter

Q-Meter We know that every inductor coil has a certain amount of resistance and the coil should have lowest possible resistance. The ratio of the inductive reactance to the effective resistance of the coil is called the quality factor   or Q-factor of the coil. So Q = XL / R = ωL / R A high value of Q is always desirable as it means high inductive reactance and low resistance. A low value of Q indicates that the resistance component is relatively high and so there is a comparatively large loss of power. The effective resistance of the coil…

Read More

Electronic Multimeters

Electronic Multimeters It is one of the most versatile general purpose instruments capable of measuring dc and ac voltages as well as current and resistances. The solid-state electronic multimeter (or VOM) generally consists of the following elements. A balanced bridge dc am­plifier and a PMMC meter. An attenuator in input stage to select the proper voltage range. 3. A rectifier for convert­ing of an ac input volt­age to proportionate dc value. 4.  An internal battery and additional circuitry for providing the capability of resistance measure­ment. 5.  A function switch for selecting various meas­urement functions of the meter such as voltage,…

Read More

Galvanometers

Electronic Galvanometers A vacuum tube or transistor amplifier, followed by a milli-ammeter may be employed as a detector. Some of such devices have arbitrary scale values, sometimes with variable gain, and are designed simply as balance indicators. The sensitivity may be of the order of a microvolt per scale division or better, and the input impedance is in the range of meg ohms, so the current drawn from the measured source is usually negligible. Such instruments have the advantages of ruggedness and portability that permit their use under conditions that would be extremely difficult for a sensitive suspended galvanometer. An­other possibility is…

Read More

Balanced Bridge Voltmeters

Balanced Bridge Voltmeters Such voltmeters can be used for measurement of both dc and ac voltages and are very popular. These voltmeters are available in both versions, vacuum tube type and transistorized type and are described below: (a) Balanced Bridge Triode VTVM. The circuit diagram of a balanced bridge triode VTVM is shown in figure. In this instrument two identical triodes T1 and T2 are used. Plate voltage is applied to both   of the triodes through two, identical resistors RL and a variable resistance RQ. Resistance R0 is so adjusted that plate voltages of both of the triodes become equal…

Read More

RMS Reading Voltmeter

True RMS Reading Voltmeter RMS value of the sinusoidal waveform is meas­ured by the average reading voltmeter of which scale is calibrated in terms of rms value. This method is quite simple and less expensive. But sometimes rms value of the non-sinusoidal waveform is required to be measured. For such a measurement a true rms reading voltmeter is required. True rms reading voltmeter gives a me­ter indication by sens­ing heating power of waveform which is proportional to the square of the rms value of the voltage. Thermo-couple is used to measure the heating power of the input waveform of which heater…

Read More

AC Voltmeters

In electronic ac voltme­ters input signal is firstly rectified and then sup­plied to the dc amplifier, as shown in figure. Sometimes signal is firstly amplified by ac amplifier and then recti­fied before supplying it to dc meter, as shown in figure. In the former case the advantage is of economical amplifiers and the arrangement is usually used in low priced voltmeters. AC Voltmeter Block Diagram Broadly ac voltmeters can be divided into three categories. 1. Average Reading AC Voltmeters. AC Voltmeter using Vacuum Tube Diode Normally ac voltmeters are average responding type and the meter is calibrated in terms of the rms…

Read More

DC Voltmeters

DC Voltmeter Block Diagram DC voltmeter mainly consists of a dc ampli­fier apart from the attenuator, as shown in figure. DC Voltmeter Block Diagram DC voltmeters can further be divided into two categories. 1. Direct Coupled Amplifier DC Voltmeter. DC Voltmeter This type of voltmeter is very common because of its low cost. This instrument can be used only to measure voltages of the order of milli-volts owing to limited amplifier gain. The circuit diagram for a direct coupled am­plifier dc voltmeter using cascaded transistors is shown in figure. An attenuator is used in input stage to select voltage range. A transistor…

Read More