Analog Multimeter – Working Principle and Construction – Electronic Instrumentation and Measurement

Do subscribe to Ekeeda channel and press bell icon to get updates about latest Engineering, HSC and IIT-JEE Mains and Advanced videos.Hello Friends,In this video we will study about analog multimeter we will study its construction its principle of working and we will see that how the analog multimeter is used for the measurement of voltage current and resistance so let us start with our topic Analog multimeter is most commonly used by engineers and technicians in the laboratories and for the repairing books now this analog multimeter as the name suggests that it is a multimeter multi means that many and meter means measurements so this analog multimeter it is an instrument which is used for making multi measurements okay means various types of measurements can be done with a single device now these measurements include the measurement of voltage current and resistance so analog multimeter can measure voltage current and resistance of various ranges you so that is the definition of a multimeter now multimeter they are of two types digital multimeter and analog multimeter the difference between these two multimeters is that digital multimeter is going to give us the output in the digital form whereas the analog multimeter gives the output in the analog form so digital form means that we will be having the digital reading over an LED or LCD the digital output will be displayed whereas analogue output means that we will be having a pointer pointer will be moving over a scale on the scale we will be having divisions and with the help of reading that scale we can get the output of the instrument so here the output is an analog output so there are two types of multimeters and here we will study about the analog multimeter so analog multimeter it also measures the voltages currents and the resistances both like DC and AC measurements can be done DC and AC voltages plus DC and AC current can be measured with it so for both DC and AC measurements these multimeters are used now we know that for the measurement of voltage the instrument which measures voltage is called the voltmeter the instrument which measures current is called amido and the instrument which measure resistance is called amido because voltage is the unit for voltage is volt the unit for current is ampere and the unit for resistance is ohms so based on that instruments are called voltmeter ammeter and o meter so because this multimeter it is measuring the voltage current and resistance so we can say that it is a combination of voltmeter ammeter and the o meter so it is sometimes also known as a V Oh

a for a metre v4 volt meter and Oh 400 medium so analog multimeter can also be called as an AVO meter now let’s come to the construction and principle of working of analog multimeters you an analog multimeter is basically a permanent magnet moving coil instrument or we can say that it is a galvanometer which is of p.m. MC type that is permanent magnet moving coil type galvanometer you so analog multimeter is basically a permanent magnet moving coil galvanometer so in this galvanometer we will be having a moving coil and this coil is moving in the magnetic field of a permanent magnet you so they’re the main parts of this galvanometer are the coil and the permanent magnet this coil is wounded on an aluminum forma and because this coil is wounded on that aluminum former and this former is allowed to move freely in the magnetic field of the permanent magnet now when current is passing through the permanent magnet magnetic field is generated and magnetic in that magnetic field the coil is being rotated okay now to this coil a pointer is attached okay so because the coil is moving in the magnetic field so as the coil moves the pointer is also going to move so pointer is attached with the coil and because of the movement of the coil the pointer is also moving and this pointer moves over a scale which is calibrated to give us the readings for the voltage for current and for the resistance so if we talk about the main components of the analog multimeter then we are having a coil a permanent magnet an aluminum former on which the coil is wounded around it then we are having a pointer and pointer is moving over a graduated scale so these are the main parts of the analog multimeter let’s see it diagram you this is the construction or the diagram of the analog multimeter which is a type of permanent magnet moving coil galvanometer you know these are the two North and South Poles of the permanent magnet and in between these because in these poles here a magnetic field will

be present in this magnetic field and aluminium former is present around this aluminum former the coil is being wounded this is the coil and to this coil a pointer is being attached and this pointer is moving over this graduated scale okay so due to this magnetic field of this magnet the coil is going to rotate and pointer is attached to the quad so coil is also moving to on the scale so on this way through this scale we can get the readings and because we are getting the analog output a pointer is moving and it isn’t indicating type of instrument the pointer is going to indicate the values so this is the annular output of the instrument so this was the construction and a working principle of the analog multimeter here you have seen that the galvanometer because in the permanent magnet moving coil instruments this should be some controlling torque and damping torque to be provided so that when the new output is being no input is being given to the instrument the pointer should rest at the zero position and as soon as the input is being removed again the pointer comes to its zero position so controlling torque and damping torque are provided here with the help of the joint springs okay you so in this analog multimeter there are two spiral Springs which are attached to the coil assembly one at the top and the other at the bottom so these Springs are going to provide the controlling torque controlling thought is needed because as soon as the input is being removed from the instrument the pointer should return immediately to the zero position so they’re returning back of the pointer to zero position is done by this controlling speaker talk okay now let’s see that’s how this analog multimeter it measures the voltage current and the resistance as I said that it is basically a permanent magnet moving coil galvanometer so this galvanometer will be converted into voltmeter ammeter and Amida for the measurement of voltage current and resistance you so with the help of suitable circuits or circuit modification the galvanometer is converted into a voltmeter for measuring voltage for measuring current and into an ohm meter for measuring the resistance as you seen that in that galvanometer we were having the scale from zero position to the maximum position so this galvanometer is going to always have its zero position on the extreme left and all the various measurements are done with respect to this zero position so on the scale of the galvanometer you have seen that zero is present on the extreme left position here zero will be there so pointer is going to give us the measurements for by deflecting it in the right hand side directions okay so now let us start with

that how the galvanometer measures the voltage current and resistance first we will see that how the voltage is measured with the help of the analog martini you now for voltage measurement the galvanometer is to be converted into a voltmeter so for that small resistances are connected in series with the galvanometer okay according to the range of voltages which we want to measure from the multimeter according to that voltage value the resistances are connected in series with the galvanometer you so voltages are measured by adding the resistances in series with the galvanometer if high voltages are to be measured then high resistances are connected if low voltages are to be measured then low resistances are connected so according to the range of voltages measured the resistance range is also married let’s see the socket for it you so for the DC voltage measurements this is for DC voltage measurements we know that V is equal to IR okay this is the own flow so voltage it varies means it is linearly related with the resistance okay if we keep the current is constant if we are changing the resistance value voltage is also going to change in the socket so here if we want to measure very high voltages then resistance value is also to be increased this is the galvanometer suppose we want to measure the voltage in the range from 0 to 10 volts then only resistance oven is selected this is the range selector switch so when low voltages are to be measured this switch is that this position if we want to measure the voltages higher than 10 volts and less than 50 volts then we will include both these resistances r1 and r2 now we will be in series with each other if we want to measure higher than this less than 250 then all these three resistances will be connected in this way the range that how much range of voltage we want to measure we are going to vary the position of this switch okay for more than thousand volts it will be for more than 500 and less than thousand it will be in between this okay so according to the range of the voltages measured this switch position is being change so voltages are measured by connecting the resistances in series with the galvanometer now this series resistance is also called multiplier because the resistance values is getting added and voltages are being multiplied here so it is called a multiplier so this series resistance can be increased or the range of voltages can be increased by increasing the number and values of the multiplier now if we see the sir the analog multimeter in that analog multimeter they will be two leads okay one lead is red in color and other leaders black in color so red is taken as for the positive connection and black is taken as

negative or for the block connection so on that multimeter we will be having two leads red and black leads so one lead is to be connected you so because they are doing the DC voltage measurements so badly it is to be connected with the voltage socket and the other lead which is the black for negative and graph that will be connected with the common point okay so this is for the DC voltage measurements now it can be used for the AC voltage measurements also and for AC voltage measurements or rectifier is used you so this rectifier is going to convert the AC into BB C for the application the circuit will be same just the good after the Saline selector switch before that we will be having a rectifier so AC will be converted into DC and then the voltage measurements will be done and readings will be displayed on the scheme so let’s see circuit for this AC voltage measurements also so the socket remains the same this is the rectifier which is going to convert the AC into DC that DC will be applied to the galvanometer and resistances will be connected according to the range of voltage measurement you so when AC voltage measurements are to be done then again we were having the two leads okay one lead is connected with the common point and other lead is connected with the voltage selection rings and we have to put the knob on the AC voltage measurement so that AC measurements can be done with it now here we have seen that we are converting the galvanometer into a voltmeter for measuring the voltage now we know that whenever B are measuring voltage with the help of a voltmeter we connect voltmeter in parallel with the device whose voltage we want to measure so here also one thing should be keep in mind that when we are measuring the voltage with the help of analog multimeter then multimeter should be connected in parallel with the circuit then voltage will be measured you so for voltage measurements analog multimeter is to be connected in parallel along with the portion whose voltage we want to measure and according to the range of the voltage measurements the range selector switches be connected so that was the voltage measurement by the analog multimeter now come to the current measurement by analog multimeter you so for the measurement of current this

analog multimeter is to be converted into an AVI so to convert this analog multimeter into an ammeter because we have to convert the galvanometer same galvanometer is converted into a meter for the measurement of current so for that o resistance a small value of resistance is connected in parallel with the galvanometer you so when we have studied the voltage measurement by the analog multimeter or resistance is connected in series with the galvanometer but here for the measurement of current or small resistance is connected in parallel with galvanometer why because we know that from the Ohm’s law V equals to IR okay and I is equals to v by r so current and resistance they are inversely proportional to each other so if you want to measure a large value of current we have to reduce the resistance okay so as the book current range which we want to measure from the multimeter is increasing the value of the resistance which is connected in parallel it’s decreasing okay you so because this resistance is connected in parallel so it is called a shunt resistance and this shunt resistance if we want to measure large currents then its value is to be decreased let’s see the circuit for it how current is measure you so for measurement of current across this galvanometer impactor resistances are connected with each other so R is less than R 2 R 2 is less than R 3 okay so if we are measuring large value of current like if you want to measure 0.25 milliampere then the range selector switch is at this position if you want to measure 10 milliampere then grain selector switches here if you want to measure currents which are between 10 Mille amperes and 250 milli amperes then we have to keep the range selector switch in between if greater than 250 milli ampere current we want to measure then the range selector switch will be kept at different position so according to the range of current which we want to measure the position of range selector switches changing okay as the current which we want to measure is increasing the value of the shunt resistance is decreasing okay this these are the positive and the negative that is the two leads of the galvanometer or the analog multimeter and this is the DC current measurement okay so for DC current measurement we will be having the two leads the red and the drag lead of the analog multimeter red lead is connected to the circuit okay to the range selector switch and the black lead is connected to the common point and the range of the current which we want to measure that can be selected with this range selector switch you so if we want to make change the ranges of the current measurement we can do with the help of varying the value of

the shunt resistance now as we know that we are converting the galvanometer into an ammeter for the measurement of current and then they will be a measuring current within our meter it is always connected in series with the circuit so here also if we want to measure the current with analog multimeter it is to be connected in series with the circuit whose current we want to measure you so that is how the analog multimeter it measures the DC current for AC current again rectifier is used rectifier is going to convert the EC back into the DC value and then but the measurements are done now let’s see that how the analog multimeter it may shows the resistance you now again the same instrument is to be used for resistant measurement so gehlbach meter is to be converted into an ohm meter so to convert the galvanometer into an ohmmeter to this galvanometer and internal battery is connected in series with the galvanometer and also there is a fixed resistance and one adjustable resistance so for voltage and current measurement we were just adding the resistance either in series or in parallel but for the ohm meter or resistance measurement we have to connect our internal battery in series with the galvanometer or fixed resistance and adjustable resistance are also used let’s see the circuit for it you so this is the circuit for the resistance measurement you can see here we are having the galvanometer or the analog multimeter in this analog multimeter we are having two leads one is the black lead and other is the deadly so red lead is red and black lead they are connected across the socket whose resistance we want to measure along with that we are having a battery they have batteries connected these are the fixed resistances and there is what adjustable resistance to adjust the zero value in the skin because here in this analog multimeter we are having an analog scale a pointer is there which is moving over a calibrated skin now by the own slope we know that V equals to I R so for measuring the resistance we have to keep the voltage and current across the circuit as constant so these fixed resistances they help in keeping the current constant in the circuit and when current is constant voltage is being applied by the battery so we can measure the resistances now here you can see that for the different ranges of resistances we want to measure the range selector switches kept at different positions okay so battery is providing us the

voltage current is limited by this fixed resistances so with that resistance can be measured so for 10 kilo ohm of resistance measurement their range selector switch is kept at this position for 1 mega ohm resistance measurement the range selector switch is kept at this position so according to that current and voltages they are varied in the circuit voltage is constant by this battery 3 volts current will be varied okay so what’s the function of the fixed resistances to limit the value of current through the circuit you and what is the function of the variable resistance R it is used for the zero adjustments of the point you now the black and the red taste each they are connected across the socket whose resistance we want to measure okay now the current which is flowing in this circuit it depends upon the resistance which we want to measure so we can say that this skill of the analog multimeter it is indicating us the value of the current not the resistance but we can calibrate it in terms of resistance so that we can directly get the readings of resistance from the scale how we can do that first we are going to make this current as constant through the circuit when current is made as constant voltage is made as constant so the readings which the word the analog multimeter is showing us here that will be the resistance readings okay you so whenever we want to measure any resistance that the black in the test leads there are eight test each they are connected across that resistance and the zero adjustment resistor that is connected so that the pointer is going to give us a zero deflection okay now paint this is zero it means that the resistance across the of the A’s leads a zero test these are short circuited with each other and then current is measured and thus resistance is very so that here the value of current is zero it means that the black in the red test leads the lead resistances negligible okay it is zero after that when it is calibrated then the resist the circuit whose resistance we want to measure across that the leaves will be connected so first the standardization or calibration is done so that the exact readings can be done and scale of the pointer gives us the reading of resistance directly so this is how the analog multimeter can be used for the measurement of resistance by converting the galvanometer into the only down now come to the sensitivity of the multimeter sensitivity is defined as the resistance value per volt of the full scale deflection means when the get the ammeter is the multimeter is showing us the full scale deflection at that time what is the resistance per unit board you our sensitivity is very important for the analog instruments because if the analog instrument is having very high sensitivity it means that it has it is having very high internal resistance so if internal resistance is high then and sensitivity is high means that very small amount of measurements can be done with it so it is a very important parameter for the instruments a high sensitivity means high internal

resistance and if internal resistance is more it means that when this instrument is connected in the circuit then this instrument is going to draw negligible current from the circuit so no current loss will be there and exact readings and accurate readings will be given to us you so correct measurements can be done if the instrument is having high sensitivity now if we talk about the sensitivity of analog multimeter it is in the range from 8 kilo ohm per volt to 20 kilo ohm okay now let’s come to the advantages and disadvantages of the analog multimeters now analog multimeters because they are having very high sensitivity so if there is very small amount of current then analog multimeters they are going to give us a quick deflection with respect to the digital multimeter you also another advantage is that all the types of measurements they can be done with a single meter only voltage current and the resistance AC and DC voltages AC DC currents they can be measured by the single meter you also if there is any increase or degrees in the levels of the signals that can also be absorbed easily on this meter because pointer is moving over the scale so if there is any increase or decrease the pointer is also going to deflect in the right-hand side or in the left hand side direction so increasing degrees can be easily absorbed so these were the advantages now comes the disadvantage the disadvantages of analog multimeters are that they are very bulky also they are costly also care has to be taken back also on that pointer and scale they are kept in a mirror okay so that the observer can easily read the mirrors easily the scale through that mirror so carefully we have to handle it because if the mirror is damaged the instrument is going to get damaged so Minton care has to be taken also while taking readings from that pointer or that from that scale the observer has to be very concentrated because if the observer is going to take the wrong readings their errors can occur in the measurement so in analog instruments there is a possibility that two human errors can occur because in digital instrument direct reading is given observer don’t need to read the take the readings from the scale so there possibility of error is less but in analog multimeters possibility of error is more also the movement of the pointer is slow as compared to the digital instruments the slowly the pointer is going to get deflected because been the controlling the dot is going to increase the level of the controlling torque then only the pointer is going to deflect so pointer movement is slow also they are a very vulnerable to the

shock and the vibrations if shocks and vibrations are present in the surrounding environment then it is going to affect the readings you also these instruments are little bit inaccurate you do the presence of the Earth’s magnetic field the magnetic field is also going to affect the readings so it is a little bit in accurate instrument so these are the disadvantages of the analog multimeters applications we already know that it can be used for the measurement of current voltage and resistance AC and DC measurements can be done with it so here in this video we studied about the analog multimeters we saw that what is it’s working principle its construction how it is used for measurement of voltage current and resistance its advantages disadvantages and its applications so I hope that this topic is now clear to you thank you