1. CONTENT 1)ANALOG MEASURING INSTRUNMETS I) ANALOG OHM-METER II) ANALOG MULTIMETER III) ANALOG AMMETER IV) ANALOG VOLTMETER V) ANALOG FREQUENCY METER 2)DIGITAL MEASURING INSTRUNMENS I) DIGITAL MULTIMETER II) DIGITAL VOLTMETER III) DIGITAL LCR METER IV) DIGITAL THERMOMETER V) DIGITAL FREQUENCY METER

2. ELECTRICAL MEASURING INSTRUNMENTS 1)ANALOG MEASURING INSTRUNMENTS 2)DIGITAL MEASURING INSTRUNMENTS

3. ANALOG MEASURING INSTRUNMENTS ANALOG MEASURING INSTRUNMENTS ANALOG OHMMETER  An ohmmeter is an electrical instruments that measures electrical resistance, the opposition to an electric current.  It has a low degree of accuracy. The statement regarding accuracy is not intended in an unfavorable sense.  An ohmmeter is useful for determining the approximate resistance of circuit components such as heater elements or machine field coils, measuring and sorting of resistors used in electronic circuits, checking of semiconductor diodes.

4. OPERATION OF AN ANALOG OHMMETER  The purpose of an ohmmeter, of course, is to measure the resistance placed between its leads. This resistance reading is indicated through a mechanical meter movement which operates an electric current.  The ohmmeter must have an internal source of voltage to create the necessary current to operate the movement and also have appropriate ranging resistors to allow just the right amount of current through the movement at any given resistance.  A more accurate type of ohmmeter has an electronic circuit that passes a constant current (1) through the resistance, and another circuit that passes measures the voltage (v) across the resistance. According to the following equation, derived from ohm’s low, the value of the resistance (r) is given by R=v/1.

5. Analog multimeter  Analog multimeters use a micrometer whose pointer moves over a scale calibrated for all the different measurements that can be made.  The main part of an analog multimeter is the D’ arsenal meter movement also known as the permanent magnet moving coil (PMMC) movement.  When the meter current ‘1m’ flows in the write wire coil, a magnetic field is produced in the coil. this electrically induced magnetic field interacts with the magnetic field of the horseshoe-type permanent magnet.  The result of such on an interaction is a force causing a mechanical torque to be exerted on the coll. Since the coil the is wound and permanently fixed on rotating cylindrical drum as shown.

6.  Each meter movement is characterized by two electrical quantities :Rm and 1.F.S. the electrical circuit symbol of the meter movement that will be as shown  The PMCC movement cannot be used directly for AC measurements since the inertia of PMCC acts as an average. Because ac current has zero average value and it produces a torque that has also zero average value.

7. Analog Multimeter Working Principle and Construction An analog multimeter is basically a permanent magnet moving coil galvanometer. There is an iron cored coil pivoted on two jeweled bearings. The coil is wound on an aluminum former or bobbin which is free to rotate in the field of a permanent magnet. An aluminum pointer is attached to the coil and bobbin assembly and moves on a graduated scale. There are two spiral springs attached to the coil assembly at the top and bottom which provide a path for the flow of current and controlling torque. An analog multimeter can measure voltage, current and resistance for which its galvanometer is converted to a voltmeter, ammeter and ohmmeter with the help of suitable circuits incorporated in it. The galvanometer used in an analog multimeter has always its pointer resting at zero position on the extreme left end various measurements are made on an analog multimeter as explained below: Voltage Measurement by a Multimetercontrolling torque Generally, a galvanometer has a current sensitivity of the order of 0.1 mA and a small internal resistance of about 500 ohms. As such it cannot measure high voltages. To measure high voltages with it, its range is extended by connecting a high resistance in series with the galvanometer as shown in the figure.

8. If the galvanometer resistance is denoted by G and I g is the full-scale deflection current and the voltage to be measured is V volts, then the value of series resistance R S is determined as under,V = I g R s + I g G or R s = (V – I g G) / I g This series resistance is also called multiplier. The voltage range can be increased by increasing the number or value of multipliers. Either a selector switch is provided to select different ranges or a number of sockets indicating the voltage range are provided in a multimeter. Current Measurement by Multimeter The same galvanometer can be used for measuring current when it is converted into an ammeter by connecting a small resistance R sh in parallel with the meter as shown in the figure. If G is the internal resistance of meter, I g its full-scale deflection current and I is the total current to be measured, then the value of shunt resistance R sh required can be found as under:(I - I g )R sh = I g G or R sh = I g G/(I - I g ) The range of ammeter can be extended to any value within limits by reducing the value of shunt resistance. In effect, a number of low resistances are connected in parallel with the meter through a selector switch as shown in the figure.

9. ANALOG AMMETER  Analog ammeters also known as current meters are metered instruments that measures current flow in amperes. Current levels are displayed on a dial, usually with a moving pointer or needle made of a soft iron. Analog ammeters provide information about current draw and current continuity in order to help users troubleshoot erratic loads and trends. They have both positive and negative leads and feature extremely low internal resistance.  The advantages of analog ammeters is that that they are suitable for use in AC and DC circuits, made of simple parts, and low cost compared to a moving coil instrument. The instruments is robust due to simple construction and the torque weight ratio is high, leading to less frictional error. Disadvantages include. Errors due to variation in temperature and frequency, relatively low values of magneticing force cause by stray fields.

10. WORKING PRINCILE OF AMMETER  Ammeters are connected in the series with circuit whose current is to be measured. The power loss in an ammeter is (I^2.Ra) where I is the current to be measured Ro is the resistance of the ammeter therefore ammeter should have low. Electricle resistance so that couse a small voltage drop and consequently absorb small power.

11. ANALOG VOLTMETER  A voltmeter is an instrument used for measuring electrical potential difference between two point in an electric current. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit. Analog voltmeters use a wide variety of means to measure voltage, with d’ Arsenal moving coil galvanometers being most common. These devices use a coil of fine wire suspended within a magnetic field. The coil rotates and moves a pointer or other indicator proportional to the applied current level.  An ideal voltmeter has two terminal and séances the voltage between the terminals where they may be connected to the circuit ideally the voltmeter has infinite resistance. It is polarized and indicates polarity as well as the magnitude of the voltage.

12. WORING PRINCIPLE OF VOLTMETER The main principle of voltmeter is that it must be connected in parallel in which we want to measure the voltage. Parallel connection is used because a voltmeter is constructed in such a way that it very high value of resistance. So if that high value of resistance. So if that high resistance. So if that high resistance is connected in series than the current flow will be almost zero which means the circuit has become open. If it is connected in parallel, than the load impedance parallel with the high resistance of the voltmeter and hence the combination will give almost the same the impedance that the load had. Also in parallel circuit we know that the voltage is same so the voltage between the voltmeter and the load is almost same hence voltmeter measures the voltage. For an ideal voltmeter, we have the resistance is to be infinity and hence the current drawn to be zero so there will be no power loss in the instruments. comes

13. ANALOG FREQUENCY METER  The action of moving coil iron analog frequency meter depends on the variation in current drawn by two parallel circuits-one inductive and other non-inductive-when the frequency changes.  Construction of moving iron frequency meter The construction and internal connections ore shown in figure. The two coil A and B are so fitted that their magnetic axes are perpendicular to each other at their centers, long and thin soft- iron pointer is pivoted, which a lings itself along the resultant magnetic field of the. Two coils. No controlling toured is provided in this instrument. It will be noted that the various circuit elements constitute a wheat stone bridge which becomes balanced at the supply frequency. Coil A has a resistance Ra in series with it and a coil LA in parallel. Similarly, RB is in series with coil B and LB is in parallel. The series inductance L helps to suppress higher harmonics in the current waveform and hence, tends to minimize the waveform errors in the indication of the instrument.

14. Working of Analog Frequency meter When the instrument is connected to the supply, currents pas through coils A and b produce apposing torques. When supply frequency Is high, currents through coil A is more whereas that through coil B is less due to the increase in the reactance offered by L B. Hence the magnetic field of coil A is stronger than that of coil B. Consequently the iron needle lies more nearly to the magnetic axis of coil a than B. For low frequencies, coil B draws more current then coil A and,hence, the needle lies more nearly parallel to the magnetic axis of B than to that of coil A. The various of frequency are followed by the pointer as explained above. The instrunment can be designed to indicate a broad of or narrow range of frequencies determined by the parameters of the circuit.

15. DIGITAL MEASURING INSTUNMENTS DIGITAL MULTIMETER  Digital multimeters have a numeric,and may also show a graphical bar representing the measured value. digital multimeters are now for more common due to their cost and precision but analog multimeters are still preferable in some cases.  Digital multimeter are instruments that are used to measures electrical quantities such as:voltage,current,resistance,frequency,temperature,capitance,time period measurements of potential in volts, resistance in ohms,ad current in amperes multimeters are used to find electronic and electrical problems. Advanced unit come with more features such as captors, diodes displaying the result in the mathematical digits from on an LED readout. It is a type d multimeter which function digitally. Digital multimeters are widely accepted worldwide as they have better accuracy levels and ranging from simple3 res to 1 by 3 to 4 res to aby2 digits handheld dmm to very special system DMM.

16. WORKING PRINCIPLE OF DIGITAL MULTIMETER As shown in block diagram, in a typical Digital multimeter the input signal i.e ac or dc voltage, current, resistance, temperature or any other parameter is converted to dc voltage within the range of the ADC. The analog to digital converter then converts the pre-scaled dc voltage into its equivalent digital numbers which will be displayed on the display unit. Sometimes, digital controller block is implemented with a microcontroller or a microprocessor manages the flow of information within the instrument. This block will coordinate all the internal functions as well as transferring information to external devices such as printers or personal computer. In the case of some hand held multimeter, some of or all of these blocks may be implemented in a VLSI circuit while A/D converter and display driver can be in the same IC.

17. DIGITAL VOLTMETER Voltmeter is an electrical measuring instrument which is used to measure potential difference between two points. The voltage to be measured may be AC or DC. Two types of voltmeters are available for the purpose of voltage measurement i.e. analog and digital. Analog voltmeters generally contain a dial with a needle moving over it according to the measure and hence displaying the value of the same. With the passage of time analog voltmeters are replaced by digital voltmeters due to the same advantages associated with digital systems. Although analog voltmeters are not fully replaced by digital voltmeters, still there are many places where analog voltmeters are preferred over digital voltmeters. Digital voltmeters display the value of AC or DC voltage being measured directly as discrete numerical instead of a pointer deflection on a continuous scale as in analog instruments. Voltmeterelectrical measuring instrumentpotential differencevoltagetypes of voltmeters

18. WORKING PRINCIPLE OF DIGITAL VOLTMETER The block diagram of a simple digital voltmeter is shown in the figure. Explanation of various blocks Input signal: It is basically the signal i.e. voltage to be measured. Pulse generator: Actually it is a voltage source. It uses digital, analog or both techniques to generate a rectangular pulse. The width and frequency of the rectangular pulse is controlled by the digital circuitry inside the generator while amplitude and rise & fall time is controlled by analog circuitry.voltage source AND gate: It gives high output only when both the inputs are high. When a train pulse is fed to it along with rectangular pulse, it provides us an output having train pulses with duration as same as the rectangular pulse from the pulse generator.

19. DIGITAL LCR METER  An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic component [1]. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive component.electronic test equipmentinductancecapacitanceresistanceelectronic component [1]impedanceequivalent series resistanceQ factor  Types of LCR meter: A.Handheld LCR meter B.Bench top LCR meter  LCR measurement by current and voltage technique In this technique, the LCR measurement of a component is done by measuring the current and voltage. Then the impedance values are found out from these two quantities..

20. There are different arrangements for low impedance and high impedance circuits, which are as follows: Both analog and digital LCR meters are available. While analog testers are cheaper, the digital variety scores on quality as it is more accurate. Working Principle of digital lcr meter We pass an AC voltage through a DUT (Device Under Test). Now the LCR meter is used to measure the voltage and the current across the DUT. The magnitude of the impedance can be calculated from the ratio of these two quantities.

21. DIGITAL thermometer METER A thermometer is a device used to measure the temperature of any particular device or living body and displays the reading. A thermometer scale can be in Fahrenheit or Celsius. Kinds of Conventional Thermometers used earlier 1.Bulb or Mercury Thermometers 2.Bimetallic Thermometers Defining Digital Thermometer :  It consists of a thermister to sense the temperature and an electronic display of the temperature. Digital thermometers are used orally, rectally or under the arm. It can read temperature from 94 ⁰ F to 105 ⁰ F.  Digital Thermometer components: 1 ) Battery 2) Thermister 3) body 4) Circuit 5) LCD  Digital thermometer Principle of Working The digital thermometer basically consists of a sensor which measures the change in resistance due to heat and converts this change in resistance to temperature.

22. Digital Thermometer Circuit: The thermister is a resistor whose resistance value varies with temperature. As the thermister gets heated, its resistance increases or decreases (depending on whether it is negative temperature coefficient or positive temperature coefficient). The analogue output from the thermister is supplied to the ADC through the wires, where it is converted to a digital signal and is then given to the Microcontroller for further processing and the output in form of temperature reading is displayed on the LCD interfaced to the microcontroller.

23. DIGITAL FREQUENCY METER Digital frequency meter is a general purpose instrument that displays the frequency of a periodic electrical signal to an accuracy of three decimal places. It counts the number events occurring within the oscillations during a given interval of time. As the preset period gets completed, the value in the counter display on the screen and the counter reset to zero. Various types of instruments are available which operates at a fixed or variable frequency. But if any frequency meter operates at a different frequency than specified range, it could carry out abnormally. For measuring low frequencies, the deflection type meters are widely used. The deflection of the pointer on the scale shows the change in frequency. The deflection type instruments are of two types: one is electrically resonant circuits and other is ratio meter.

24. OPERATING PRINCIPLE OF DIGITAL FREQUENNCY METER A frequency meter has a small device which converts the sinusoidal voltage of the frequency into a train of unidirectional pulses. The frequency of input signal is the displayed count, averaged over a suitable counting interval out of 0.1, 1.0, or 10 seconds. These three intervals repeat themselves sequentially. As the ring counting units resets, these pulses pass through the time-base-gate and then entered into the main gate, which opens for a certain period of time interval. The time base gate prevents a divider pulse from opening the main gate during the display time interval. The main gate acts as a switch when the gate is open, pulses are allowed to pass. When the gate is closed, pulses are not allowed to pass that means the flow of pulses get obstructed. The functioning of the gate is operated by the main-gate flip-flop. An electronic counter at the gate output that counts the number of pulses passed through the gate while it was open. As the next divider pulse is received at main gate flip-flop, the counting interval ends and divider pulses are locked out. The resultant value displayed on a display screen which has the ring counting units of scale-of-ten circuits and each unit is coupled to a numeric indicator, which provides the digital display. As the reset pulse generator is triggered, ring counters get reset automatically and the same procedure starts again. The range of modern digital frequency meter is between the range from10 4 to 10 9 hertz. The possibility of relative measurement error ranges between from 10 - 9 to 10 -11 hertz and a sensitivity of 10 -2 volt.voltageflip-flop