Electrical Test Equipment PDF

**Electrical Test Equipment** Ammeter ------- Definition A device or instrument that is used to measure the current is called the ammeter. The unit of the current is ampere. So this device measures the current flow in ampere is named as an ammeter or ampere meter. The internal resistance of this...

**Electrical Test Equipment** Ammeter ------- Definition A device or instrument that is used to measure the current is called the ammeter. The unit of the current is ampere. So this device measures the current flow in ampere is named as an ammeter or ampere meter. The internal resistance of this device is '0' however in practical; it has some amount of internal resistance. The measuring range of this device mainly depends on the resistance value. Operating Principle The working principle of an ammeter mainly depends on resistance as well as reactance. This device includes extremely less impedance because it must include less amount of voltage drop across it. It is connected in series because the flow of current within the series circuit is the same. The main function of this device is to measure the flow of current with the help of a set of coils. These coils have very low resistance & inductive reactance. Ammeter Circuit Diagram The **construction of ammeter** can be done in two ways like series and shunt. The following circuit represents the basic circuit diagram and the connection of the ammeter circuit in series and parallel** **are shown below. Once this device is connected in series in the circuit, and then the total measuring current will flow through the meter. So the loss of power occurs within ammeter due to their internal resistance & the measuring current. This circuit includes less resistance so less voltage drop will occur within the circuit. The resistance of this device is kept small due to the reasons like the total measuring current will flow throughout the ammeter and less voltage drop will occur across the device. When the high current flows through this device, the internal circuit of the device will be damaged. To overcome this problem in the circuit, the shunt resistance can be connected within parallel to the ammeter. If the huge measuring current supplies throughout the circuit, the main current will pass throughout the shunt resistance. This resistance will not have an effect on the function of a device. Application The applications of ammeter include the following. 1\. The applications of this device will range from the schools to industries. 2\. These are used to measure the current flow in the buildings to ensure that the flow is not too low or too high. 3\. It is used in manufacturing and instrumentation companies to check the functionality of the devices 4\. It is used with a thermocouple to check the temperature. 5\. Electricians frequently use these devices to check the faults of the circuits in the building. Safety: ------- 1\. Always turned off the power before connecting ammeter to a circuit. 2\. An analog ammeter must never be connected in parallel with any of the circuit components. if connected in parallel, the fuse in the ammeter will blow and may seriously damage the meter or the circuit. also, never connect an ammeter directly to a voltage source. If an analog voltmeter is connected in series with a circuit, a large current can flow through the meter and might damage it. Voltmeter --------- Definition A voltmeter is an instrument used to measure voltage or electrical potential difference between two points in basic electric circuits. Analog voltmeters move a pointer across a scale in proportional to the voltage of the circuit. Voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts.  Operating Principle Voltmeter works on the principle of Ohm's law, which states that the voltage across a resistance is directly proportional to the current passing through it. In order to implement it in real time, we form the construction of a galvanometer, such that a coil is suspended in a magnetic field. We know that the current passing through the circuit also passes through the coil and the needle that is attached to the coil which deflects on the reading scale moves, and the movement of the needle is directly proportional to the current passing through it. This construction is shown in the figure below: In orders to convert this ammeter into a galvanometer, we attach a large resistance in series with the coil of the galvanometer. This resistor acts to minimize the coil interference with the circuit. Since according to ohms law the voltage is directly proportional to the resistance, so the voltage consumed by the galvanometer is minimized and a very accurate voltage drop across the circuit is measured.  Application Voltmeters are one of the most widely used measuring devices especially in circuitry and hardware where very precise measurement is required. Safety: ------- If an analog voltmeter is connected in series with a circuit, a large current can flow through the meter and might damage it. Ohmmeter -------- Definition An ohmmeter can be defined as, it is one kind of electronic device mainly used for calculating electrical resistance of a circuit, and the unit of resistance is ohm. Electrical resistance is a calculation of how much an object resists allowing the flow of current through it. There are different types of meters available with different sensitivity levels such as micro, mega and milli-ohmmeters. The micro-ohmmeter is used for calculating very low resistances with high precision at specific test currents, and this ohmmeter is used in bonding contact applications.  Operating Principle The working principle of ohmmeter is, it comprises of a needle and two test leads. The needle deflection can be controlled with the battery current. Initially, the two test leads of the meter can be shorted together to calculate the resistance of an electrical circuit. Once the two leads of the meter are shorted, then the meter can be changed for appropriate action in a fixed range. The needle comes back to the highest point on the meter scale, and the current in the meter will be highest. An ohmmeter circuit diagram is shown below. Once the testing of the circuit is done then the test leads of the meter must be detached. Once the two test leads of the meter are connected to the circuit then the battery gets discharged. When the test leads get shorted then the rheostat will be adjusted. The meter needle can be reached to the lowest position that is zero, and then there will be zero resistance among the two test leads. Types of Ohmmeter ----------------- The classification of this meter can be done based on the application in three types namely series type ohmmeter, shunt type ohmmeter, and multi-range type ohmmeter. The brief discussion of meters is given below. ### 1) Series Type Ohmmeter In series type ohmmeter, the component which we want to measure can be connected with the meter in series. The resistance value can be calculated through the shunt resistor R2 using D'Arsonval movement which is connected parallel. The R2 resistance can be connected in series with the battery as well as R1 resistance. The measuring component is connected in series by the two terminals A as well as B. Whenever the measuring component value is zero then there will be a huge flow of current through the meter. In this situation, the shunt resistance can be corrected until the meter specifies the full-load current. For this current, the needle turns aside in the direction of 0 ohms. Whenever the measuring component is detached from the circuit then the circuit resistance turns into the unlimited & flow of current in the circuit. The needle of the meter deflects towards the infinity. The meter illustrates the infinite resistance when there is no flow of current & the zero resistance once the huge flow of current through it. Whenever the measuring component is connected in series with the circuit, and the resistance of that circuit is higher, the meter needle will deflect in the direction of the left. And if the resistance is little, then needle turn aside in the direction of right. ### 2) Shunt Type Ohmmeter The connection of shunt type ohmmeter can be done whenever the calculating component is connected in parallel with the battery. This type of circuit is used to calculate the low-value resistance. The following circuit can be built with the meter, the battery, and the measuring component. The measuring component can be connected across the terminals A & B. When the resistance value of the component is zero then the current in the meter will become zero. Similarly, when the resistance of the component becomes vast then the flow of current through the battery & the needle illustrates the full-scale deflection in the direction of the left. This type of meter has no current on the scale in the direction of left as well as the infinity spot in their right direction. ### 3) Multi-Range Ohmmeter The multi-range ohmmeter range is very high, and this meter includes an adjuster, and the range of a meter can be selected by an adjuster based on the requirement. For instance, consider we utilize a meter to calculate the resistance below 10 ohms. So initially, we need to fix the resistance value to 10 ohms. The measuring component is connected with the meter in parallel. The resistance magnitude can be decided by the deflection of the needle. Application The uses of the ohmmeter include the following. Safety: ------- Prior to connecting an ohmmeter to a circuit, make sure the power is turned off. Wattmeter --------- Definition The wattmeter is an instrument which measures DC power or true AC power.. Operating Principle The wattmeter uses fixed coils to indicate current, while the movable coil indicates voltage Coils L11 and L12 are the fixed coils in series with one another and serve as an ammeter. The two I terminals are connected in series with the load. The movable coil Lv, and its multiplier resistor Rs, are used as a voltmeter, with the V terminals connected in parallel with the load. The meter deflection is proportional to the VI, which is power. Wattmeters are rated in terms of their maximum current, voltage, and power. All of these ratings must be observed to prevent damage to the meter. Application The applications of ammeter include the following. 1. 2. 3. 4. **Ampere-Hour Meter** --------------------- The ampere-hour meter registers ampere-hours and is an integrating meter similar to the watt-hour meter used to measure electricity usage in a home. Typical ampere-hour meters are digital indicators similar to the odometer used in automobiles. The amperehour meter is a direct current meter that will register in either direction depending on the direction of current flow. For example, starting from a given reading, it will register the amount of discharge of a battery; when the battery is placed on charge, it will operate in the opposite direction, returning once again to its starting point. When this point is reached, the battery has received a charge equal to the discharge, and the charge is stopped. It is normally desired to give a battery a 10% overcharge. This is accomplished by designing the ampere-hour meter to run 10% slow in the charge direction. These meters are subject to inaccuracies and cannot record the internal losses of a battery. They attempt to follow the charge and discharge, but inherently do not indicate the correct state of charge. Similar to an ammeter, the ampere-hour meter is connected in series. Although the ampere-hour meters were used quite extensively in the past, they have been largely superseded by the voltage-time method of control. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Power Factor Meter** A power factor meter is a type of electrodynamometer movement when it is made with two movable coils set at right angles to each other. The method of connection of this type of power factor meter, in a 3Φ circuit,. The two stationary coils, S and S1, are connected in series in Phase B. Coils M and M1 are mounted on a common shaft, which is free to move without restraint or control springs. These coils are connected with their series resistors from Phase B to Phase A and from Phase B to Phase C. At a power factor of unity, one potential coil current leads and one lags the current in Phase B by 30°; thus, the coils are balanced in the position. A change in power factor will cause the current of one potential coil to become more in phase and the other potential coil to be more out of phase with the current in Phase B, so that the moving element and pointer take a new position of balance to show the new power factor.  **Synchroscope** A synchroscope indicates when two AC generators are in the correct phase relation for connecting in parallel and shows whether the incoming generator is running faster or slower than the on-line generator. The synchroscope consists of a two-phase stator. The two stator windings are at right angles to one another, and by means of a phase splitting network, the current in one phase leads the current of the other phase by 90°, thereby generating a rotating magnetic field. The stator windings are connected to the incoming generator, and a polarizing coil is connected to the running generator. The rotating element is unrestrained and is free to rotate through 360°. It consists of two iron vanes mounted in opposite directions on a shaft, one at the top and one at the bottom, and magnetized by the polarizing coil. If the frequencies of the incoming and running generators are different, the synchroscope will rotate at a speed corresponding to the difference. It is designed so that if incoming frequency is higher than running frequency, it will rotate in the clockwise direction; if incoming frequency is less than running frequency, it will rotate in the counterclockwise direction. When the synchroscope indicates 0° phase difference, the pointer is at the \"12 o\'clock\" position and the two AC generators are in phase.  **Multimeter** The multimeter is a portable single instrument capable of measuring various electrical values including voltage, resistance, and current. The volt-ohm-milliammeter (VOM) is the most commonly used multimeter. The typical VOM has a meter movement with a full scale current of 50 µA, or a sensitivity of 20 KΩ/V, when used as a DC voltmeter. A single meter movement is used to measure current, AC and DC voltage, and resistance. Range switches are usually provided for scale selection (e.g., 0-1V, 0-10V, etc). **Megger** The megger is a portable instrument used to measure insulation resistance. The megger consists of a hand-driven DC generator and a direct reading ohm meter. A simplified circuit diagram of the instrument. The moving element of the ohm meter consists of two coils, A and B, which are rigidly mounted to a pivoted central shaft and are free to rotate over a C-shaped core. These coils are connected by means of flexible leads. The moving element may point in any meter position when the generator is not in operation. As current provided by the hand-driven generator flows through Coil B, the coil will tend to set itself at right angles to the field of the permanent magnet. With the test terminals open, giving an infinite resistance, no current flows in Coil A. Thereby, Coil B will govern the motion of the rotating element, causing it to move to the extreme counter-clockwise position, which is marked as infinite resistance. Coil A is wound in a manner to produce a clockwise torque on the moving element. With the terminals marked \"line\" and \"earth\" shorted, giving a zero resistance, the current flow through the Coil A is sufficient to produce enough torque to overcome the torque of Coil B. The pointer then moves to the extreme clockwise position, which is marked as zero resistance. Resistance (R1) will protect Coil A from excessive current flow in this condition. When an unknown resistance is connected across the test terminals, line and earth, the opposing torques of Coils A and B balance each other so that the instrument pointer comes to rest at some point on the scale. The scale is calibrated such that the pointer directly indicates the value of resistance being measured.  Parts of Analog Multimeter  Pointer -- indicates the values read from the scale. Scale -- shows the value of what is being measured Zero ohm adjuster -- adjusts the pointer to the right side of the scale Range Selector Knob -- allows changing the function and scale Test Probes -- Positive probe (red) and negative probe (black) are used to connect to the circuit or device under test. Zero position adjuster -  A device for **adjusting** the pointer **position** of an instrument or meter to read **zero** when the measured quantity is **zero**. **1) ACV** --- is an AC voltmeter (enclosed with a red bracket) on upper-right side. It has 4 range of selections. Here you can select: a. **10** --- Select this range if the voltage to be measured is less than 10 volts ac. b. **50** --- Select this range if the voltage to be measured is less than 50 volts ac but more than 10 volts ac. c. **250** --- Select this range if the voltage to be measured is less than 250 volts ac but more than 50 volts ac. d. **750** --- Select this range if the voltage to be measured is less than 750 volts ac but more than 250 volts ac. **2) DCV** --- is a DC voltmeter (enclosed with a white bracket) on upper-left side. It has 6 range of selections. Here you can select: a. **0.1** --- Select this range if the voltage to be measure is less than 0.1 volts dc. You may have noticed how this range intersects with DCA (Dc ammeter section). Therefore it can be also used as a a dc ammeter but only within this range. b. **0.25** --- Select this range if the voltage to be measured is less than 0.25 volts dc but more than 0.1 volts dc. c. **2.5** --- Select this range if the voltage to be measured is less than 2.5 volts dc but more than 0.25 volts dc. d. **10** --- Select this range if the voltage to be measured is less than 10 volts dc but more than 2.5 volts dc. e. **50** --- Select this range if the voltage to be measured is less than 50 volts dc but more than 10 volts dc. f. **250** --- Select this range if the voltage to be measured is less than 250 volts dc but more than 50 volts dc. g. **1000** --- Select this range if the voltage to be measured is less than 1000 volts dc but more than 250 volts dc. **3) DCA** --- is a DC ammeter (enclosed with a white bracket) on lower-left side. It has 4 range of selections. Here you can select: a. **50μ** --- Select this range if the current to be measured is less than 50 microampere. b. **2.5m** --- Select this range if the current to be measured is less than 2.5 milliampere but more than 50 microampere. c. **25m** --- Select this range if the current to be measured is less than 25 milliampere but more than 2.5 milliampere. d. **0.25** --- Select this range if the current to be measured is less than 250 milliampere but more than 25 milliampere. **4) Ω** **--- **is an ohmmeter (enclosed with a white bracket) on lower-right side. It has 4 range of selections. **4) Ohmmeter** --- is an ohmmeter(enclosed with a yellow bracket) on lower-right side. It has 4 range of selections. Here you can select: a. **x1** --- Select this range if the resistance to be measured is very low, ranging from 0 ohms (short circuit) to 1kΩ. b. **x10** --- Select this range if the resistance to be measured is ranging from 10Ω to 10kΩ. c. **x100** --- Select this range if the resistance to be measured is ranging from 100Ω to 100kΩ. d. **x1k** --- Select this range if the resistance to be measured is ranging from 1kΩ to 1MΩ. **There are several practice that you need to know while making it as a habit when using a multi-tester.** **1.** Before using a multi-tester, make sure the pointer points to infinity position. It should look exactly like the image above. By default, it should point exactly to infinity scale since it was properly set by the manufacturer. If not, slowly turn the "zero position adjuster" until it points exactly to infinity position. **2.** Before using an ohmmeter (it doesn't matter what range you have used), always short the test pins (red and black) to test if the pointer points to zero resistance. If not, turn the "zero ohm adjuster knob" until it points to zero. **3.** Be careful in using an ohmmeter --- make sure you are doing resistance measurement and not voltage measurement. Ohmmeter's internal circuit is powered by a 3v battery. Accidental voltage measurement will amplify the current inside the circuit and can cause severe damage. **4.** Before doing voltage measurement, be sure to identify whether it is an AC (alternating current) or DC (Direct Current) voltages. **5.** Before doing voltage measurements, make sure you have selected the correct range so that the voltage to be measured is lower than the range being selected. **How to read Multimeter** **Ohmmeter Reading** Resistance scale is located in the top most part of a meter panel. You may have noticed a descending order of number. From left (∞) to right (0). In practice, reading values always starts from zero. Therefore we will read resistance values from right to left which is zero (0) to infinity (∞). resistance scale is located in the top most part of a meter panel. You may have noticed a descending order of number. Since we will read resistance values from right to left, see to it that the gaps between numbers are not equally divided. Please don't get so confused why it is not equal. In fact, it's not a big deal. After all what we need to learn is the value of each scale between each numbers. Those small vertical lines that divide on each number is a scale. Each scale has a value with respect to each nearest number. To fully understand it, we will make a list of numbers from zero (0) to infinity (∞) with its individual scale and value. **0--1** --- is divided by 5 scales. Each scale has a value of 0.2 ohm. Therefore 0.2 ohm multiplied by 5 scales is equal to **1 ohm**. **1--2** --- also divided by 5 scales. Each scale has a value of 0.2 ohm. Therefore 0.2 ohm multiplied by 5 scales is equal to **1 ohm**. Adding all the value from zero, we get a total of 2 ohms. **2--5** --- is divided by 6 scales. Each scale has a value of 0.5 ohm. Therefore 0.5 ohm multiplied by 6 scales is equal to **3 ohms**. Adding all the value from zero, we get a total of 5 ohms. **5--10** --- is divided by 10 scales. Each scale has a value of 0.5 ohm. Therefore 0.5 ohm multiplied by 10 scales is equal to **5 ohms**. Adding all the value from zero, we get a total of 10 ohms. **10--20** --- is divided by 10 scales. Each scale has a value of 1 ohm. Therefore 1 ohm multiplied by 10 scales is equal to **10 ohms**. Adding all the value from zero, we get a total of 20 ohms. **20--30** --- is divided by 5 scales. Each scale has a value of 2 ohms. Therefore 2 ohms multiplied by 5 scales is equal to **10 ohms**. Adding all the value from zero, we get a total of 30 ohms. **30--50** --- is divided by 10 scales. Each scale has a value of 2 ohms. Therefore 2 ohms multiplied by 10 scales is equal to **20 ohms.** Adding all the value from zero, we get a total of 50 ohms. **50--100** --- is divided by 10 scales. Each scale has a value of 5 ohms. Therefore 5 ohms multiplied by 10 scales is equal to **50 ohms.** Adding all the value from zero, we get a total of 100 ohms. **100--200** --- is divided by 5 scales. Each scale has a value of 20 ohms. Therefore 20 ohms multiplied by 5 scales is equal to **100 ohms.** Adding all the value from zero, we get a total of 200 ohms. **200--500** --- is divided by 4 scales. Each scale has a value of 75 ohms. Therefore 75 ohms multiplied by 4 scales is equal to **300 ohms.** Adding all the value from zero, we get a total of 500 ohms. **500--1k** --- is not divided by a scale. Therefore from 500, you will get the value of 1 kilo-ohms (1K) by adding 500 ohms. So, it is very obvious that the gap between 500 ohms and 1k is **500 ohms.** Adding all the value from zero, we get a total of 1 kilo-ohms (1K) **1k-2k** --- is not divided by a scale. Therefore from 1K, you will get the value of 2k by adding 1K. So, the gap is obviously **1 kilo-ohms (1K).** Adding all the value from zero, we get a total of 2 kilo-ohms (2K). Any value that goes beyond 2K or 2 kilo-ohms value has a very high resistance and exceed the **x1 multiplier** range of an ohmmeter. Please note that the highest resistance scale is only limited to 2k or 2 kilo-ohm resistance. If you need to measure resistance which is higher than 2 kilo-ohms, set the ohmmeter range to higher **multiplier** range and so on. **What is a multiplier?** These are the 4 range of an ohmmeter, as you can **see in the image below**. An ohmmeter is divided by four main settings. a) **x1** --- select this range so that any value in the resistance scale is multiplied by 1. b) **x10** --- select this range so that any value in the resistance scale is multiplied by 10. c) **x100** --- select this range so that any value in the resistance scale is multiplied by 100. d) **x1k** --- select this range so that any value in the resistance scale is multiplied by 1k or 1 thousand. **Does each range is has its own sensitivity?** - - **What range should be used in resistance measurement?** - - - -  Example:     **Voltmeter Reading** Voltmeter scale is located below the ohmmeter scale. Reading values of voltmeter starts from left to right always starts from zero. Analog voltmeter is a linear scale meaning it is divided into equally spaced segments. Here you can select: a. **0.1** --- Select this range if the voltage to be measure is less than 0.1 volts dc. You may have noticed how this range intersects with DCA (Dc ammeter section). Therefore it can be also used as a a dc ammeter but only within this range. b. **0.25** --- Select this range if the voltage to be measured is less than 0.25 volts dc but more than 0.1 volts dc. c. **2.5** --- Select this range if the voltage to be measured is less than 2.5 volts dc but more than 0.25 volts dc. d. **10** --- Select this range if the voltage to be measured is less than 10 volts dc but more than 2.5 volts dc. e. **50** --- Select this range if the voltage to be measured is less than 50 volts dc but more than 10 volts dc. f. **250** --- Select this range if the voltage to be measured is less than 250 volts dc but more than 50 volts dc. g. **1000** --- Select this range if the voltage to be measured is less than 1000 volts dc but more than 250 volts dc.  Voltmeter range Example:      Note: Select the proper setting before using multimeter if it is DC or AC. ---------------------------------------------------------------------------------------------------------- ------------------  ***Assessment*** ---------------------------------------------------------------------------------------------------------- ------------------ 1\. Explain the operating principle of voltmeter, ohmmeter and ammeter. 2\. Explain the operating principle for a wattmeter, ampere-hour meter, power factor meter, and synchroscope. 3\. How to connect ammeter and voltmeter into the circuit?