1. "position": 3, Digital multimeter is a test equipment which offers several electronic measurement task in one tool. , adjust the meter dial to the suitable function to DC Voltage or AC voltage. Adjust the meter dial to the resistance mode. Voltage requires only that power is applied, the load does not need to be active. "@id": "https://electricalacademia.com/instrumentation-and-measurements/digital-multimeter-working-principle/", All multimeters use the same rule to determine resistance whether they are analog or digital multimeters. There are different types of registers available based on their power rating and resistance value; colour codes will specify the value of each resistor. All multimeters measure ac and dc voltage (voltmeter), ac and dc current (ammeter), and resistance (ohmmeter). There are two main types of multimeters. The battery supplies the current flow that is eventually measured by the meter. Testing for voltage is carried out to ensure the effectiveness of the electrical system. Testing Resistance (Ohms) with a Digital Multimeter. There are pushbuttons on the meter to indicate which type of measurement is being made, and The digital multimeter or DMM offers two methods for measuring resistance: 2–wire and 4–wire ohms. Introduction. Touch the component under test using the leads, Digital Frequency Meter Working Principle, Difference between Digital and Analog Multimeter, Fourier Transform and Inverse Fourier Transform with Examples and Solutions, Phase Rotation Meter | Phase Sequence Indicator. A quick digital multimeter tutorial on making resistance measurements. To measure resistance by the multimeter, a suitable range is selected. It is suitable for insulation resistance measurement. … Over time, corrosive soils with high moisture and salt content and high temperatures can degrade ground rods and their connections. "@id": "https://electricalacademia.com/category/instrumentation-and-measurements/", Analog meters use a printed linear or nonlinear background and a mechanical pointer. The multimeter can now be used to measure the resistance of a component connected between these two wires 2. If the voltage reading is out of specifications then the problem can be found using the voltmeter to isolate the load and find if there is a problem with the source or the load. There are a wide range of resistors available based on their power rating and resistance value, the value of each resistor … For measurement of resistance, the unknown resistance is connected in series with the meter and across a battery, such that the current passing through the meter is directly proportional to the unknown resistance. Resistance testing is done to ensure the load or circuit being tested is complete. There two types of digital multimeters (DMM): First, figure out whether the application being testing utilizes AC or DC voltage. On a multimeter that is not auto-ranging, there will be a number of different ranges marked on the multimeter dial, e.g. Watts is calculated by multiplying volts by the amps. Resistance (Times 1k or X1k) Scale Meter reads about 150, multiply that by 1000 and you have 150K Ohms. Note that the zero value for ohm measurement (top scale) is to the extreme right (all the other zero values are on the extreme left). },{ If there is only one path to ground, the stakeless method will not provide an acceptable value and the fall-of-potential test method must be used.The earth ground tester works on the principle that in parallel/multi-grounded systems, the net resistance of all ground paths will be extremely low compared to any single path (the one under test). resistance. Initially, there are two types of multimeters, analog and digital. The volt-ohm-milliammeter (VOM) is the most commonly used multimeter. Did you find apk for android? The auto-ranging digital multimeter (DMM) only requires you to choose your electrical quantity you are attempting to measure, make sure you are properly placing your leads into the correct terminals and then reading the LCD display. How to Measure Resistance with Multimeter: One of the most use and unavoidable component in electronics are Resistors. Then the meter leads are shorted, and variable resistance r is adjusted to give full-scale deflection. A digital multimeter (DMM) is a multifunctional meter that displays its electrical quantitative values on an LCD screen. In the process of measuring resistance, the test leads are inserted in the meter jacks. { Parallel connection is used because a voltmeter is constructed in such a way that it has a very high value of resistance . Current can be tested in several ways; the most reliable procedure is using a clamp meter, shown in figure 4. No matter the loss of varactor diode capacity or internal open-circuit fault, it … The measurement of DC resistance can reflect the quality of joint welding, whether there is turn-to-turn short-circuit and each tap changer is contacted well. Because of its design, a processor can be built into the meter which allows the user to take measurements of frequency, the inductance of a coil, capacitance of a capacitor, and a host of other high functional electrical measurements. The pointer moves as a result of the flow of current through a built-in coil, the presence of electrical pressure, or the internal power source that is needed for resistance measurements. This technique is generally used for resistance values below 200M ohms. 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. Be sure to wear your PPE as we always assume a circuit is “live” until proven otherwise. The magnitude of } ] A multimeter is the most popular electronic measuring instrument which has some kinds of measurement functions included in one package. Digital Multimeter. Here is a step by step guide on how to use a multimeter to test for voltage: Testing for current is used when there is no physical way to tell if a load is doing its job because there are no indicators or the load is located in a hazardous area. A multimeter can be used to measure electrical functions such as voltage, current, resistance, continuity and some are able to measure electrical frequency. Based on the display, you could recognize that there are two types of multimeters available on the market. Electrical resistance is measured by either of two methods: constant current or constant voltage. Afterward, adjust the meter dial to the suitable function to DC current or AC current. For measurement of resistance, the unknown resistance is connected in series with the meter and across a battery, such that the current passing through the meter is directly proportional to the unknown resistance. As for measuring voltage on an auto-ranging multimeter, there will be only one dial setting for measuring resistance. As the test continues the measurement will steady. Position and reposition the test till a dependable reading appears on the meter LCD. During the measurement, if the multimeter swings slightly to the right or the resistance value is zero, it means that the varactor diode under test has a leakage fault or has been broken down. Apart from that, these digital… a circuit that has power switched on to it. Testing blindly is dangerous and counterproductive. It can also be used for measurement of audio power. View the reading and note the unit of measurement, ohms, kilohms, or megohms. If the value being measured is unknown, then set the range to the maximum available number. Resistance Measurement The part of the circuit diagram of Multimeter, which can be used to measure resistance is shown in below figure. Never measure resistance on a live circuit – i.e. The ohmmeter is created from a DC current meter by the addition of a group of resistors (called multiplier resistors) and an internal battery. If the dial selected is in the range of the resistor, it displays a proper reading. Digital Multimeter Working. } 1. Otherwise, the multimeter will show wrong resistance reading. It’s always better to remove the component to measure the resistance. The main principle of voltmeter is that it must be connected in parallel in which we want to measure the voltage. Principle of measuring resistance with a multimeter Home; About us; Products. Turn the power off in the circuit being tested. Fig. Figure 1: Measurement of resistance, voltage and current with a multimeter For resistance measurements, one connects the DMM over the resistor. "url": "https://electricalacademia.com/instrumentation-and-measurements/digital-multimeter-working-principle/", A complete circuit means there is no break or opening in the wires connected to the load or the internal components of the device being tested. When a resistance is placed between the leads, the readout increases according to how much current that resistance allows to flow. PRINCIPLE AND TYPES OF ANALOG AND DIGITAL INSTRUMENTS A multimeter ora multitester, also known as a volt/ohm meter or VOM is , an electronic measuring instrument that combines several measurement functions in one unit. In fact other forms of test equipment that measure resistance also use the same basic principle.The basic idea is that the multimeter places a voltage at the two probes and this will cause a current to flow in the item for which the resistance is being measured. },{ The resistance seen by the voltage source is approximately Ra, which is very small so the current Ia would be very large, thus exceeding the maximum 1. Plug the test leads into the suitable terminal. Dec 4, 2015 - Explore Himanshi gupta's board "Fluke Multimeter Measurement", followed by 124 people on Pinterest. Even though it reads out resistance, the ohmmeter is still a current-measuring device at heart. Cropico is a world leader in low resistance measurement; we produce a comprehensive range of low resistance ohmmeters and accessories which cover most measurement applications. A multimeter, shown in Figure 1, is a device used to measure two or more electrical quantities. Analog Multimeter Basics and Measuring Resistance Analog Meter Precautions •Do not Jar, manhandle, drop or pile tools or any thing else on your meter. Proper protective equipment must be worn before testing can be done. Select volts AC (V~), volts DC (V—), mvolts (V—) as desired Notice that for voltage measurements one puts the multimeter in parallel with the circuit element so that one measures the voltage across the element. It doesn't matter which probe goes where; resistance is non-directional. The resistance testing and continuity testing are also a good way to check for short-circuits and the ground fault which are events that cause circuit breakers to trip, fuses to blow, and possible injury to workers in the field. The DT830B has five range settings for measuring resistance with the highest setting being 2000-kilo ohms (or two mega ohms). This measurement display can show three readings: 1, 0.00, or the actual resistance value. The ohmmeter is created from a DC current meter by the addition of a group of resistors (called multiplier resistors) and an internal battery. The meter’s battery sends a current flow through the unknown resistance, the meter’s internal resistors, and the current meter. The following figure represents the digital multimeter block diagram with all the functional blocks. "@id": "https://electricalacademia.com", 4. adjust the range of the measurement using the level up and down keys Note: Be very careful that when set up to measure current you don’t put the DMM in parallel with the voltage source (see Fig. Resistance measurement Figure 1: A digital multimeter measures resistance by passing a constant current through the device under test and scaling the indicated voltage drop to the accordant resistance value. A common multimeter at least has the ability to measure current, voltage, and resistance. Because of its design, a processor can be built into the meter which allows the user to take measurements of frequency, the inductance of a coil, capacitance of a capacitor, and a host of other high functional electrical measurements. Some can also measure other electrical quantities such as frequency or even temperature. "url": "https://electricalacademia.com/category/instrumentation-and-measurements/", To measure the resistance, current flows from a constant current source through the unknown resistor and the voltage across the resistor are amplified and fed to an Analog to Digital Converter and the resultant output in form of resistance is displayed on the digital display. Multimeters 101: Basic Operation, Care and Maintenance and Advanced Troubleshooting for the Skilled Trades, Next: Introduction to Continuity Measurements, Creative Commons Attribution 4.0 International License. Adjust the range to the number little higher than the predictive value. Start with the lowest setting. Remove or isolate the component to be tested. EE101: Multimeter Notes In the lab we will use a digital multimeter (DMM) to measure resistance, voltage, and current in our circuits. The multimeter computes the resistance between the different paths in a circuit. When the voltage is tested and found to be present at the load, it doesn’t tell the whole story until a current is measured. The measurement of very large or very small quantities is always difficult, and resistance measurement is no exception. The auto-ranging digital multimeter is more widely used due to its ease, high functionality, and quick display readings achieved without the user completing the calculations. Turn the meter off when testing is complete to prolong battery life. 5. This is because of the small resistance of the ammeter (Ra). This multimeter uses several circuits namely the principle of divider circuit for voltage and resistance measurement, the capacitor charging principle to measure capacitance and use the ACS712-30T sensor for current measurement. It is also known as the voltmeter or Ohm meter or Volt Ohm meter. Since current can flow either way through a pure resistance, there is no polarity requirement for attaching the meter leads. A digital multimeter is used to measure or give a good indication of current flowing. Experimental principle. Dirt, bodily contact, and poor test lead connection can considerably alter the readings. By measuring the resistance it is possi… Resistance testing is sometimes referred to as continuity testing. { So, although the ground system had low earth ground resistance values when initially installed, […] Apply the leads to the open circuit current and observe the measurement. Touch the probe tips across the component or portion of the circuit. The meter should display zero or a very small amount of resistance for the test leads. More recently, a new type of precision multimeter, the Fluke 8508A Reference Multimeter, has been developed with the accuracy and stability of metrology grade instruments approaching measurement levels available There two types of digital multimeters (DMM):  scalable digital multimeter and auto-ranging digital multimeter as shown in Figure 1. When testing voltage there is an expected voltage reading to look for. "@type": "BreadcrumbList", You can find new, There are two main types of multimeters. Connect the tips of the probes across the break in the component or portion of the circuit for which you want to determine resistance. "name": "Instrumentation" With the leads apart, the meter should display OL or I, depending on the manufacturer. If you knew your resistor colour code, then you can set the range precisely, otherwise the standard procedure is to start with the lowest range and work your way up until you get a reading. "@context": "http://schema.org", It is important to understand a load consumes power which is measured in watts. High Resistance Measurement (>100KΩ) Under this condition, the resistance between test leads is zero; therefore, the scale of … If no continuity exists, the DMM does not beep. Parallel connection is used because a voltmeter is constructed in such a way that it has a very high value of resistance. Beginners are often confused and do not know which setting to use. Place one probe at each end of the circuit or component you want to test. Note:  For current measurements above 1A, normally clamp meter is used while for current less than 1A, a standard DMM is used. Analog meters are a multifunctional multimeter that operates based on electrical mechanical movement. There are pushbuttons on the meter to indicate which type of measurement is being made, and other pushbuttons to select … Failure to observe these values will result in inaccurate readings and possible damage to the meter. Analog meters use a printed linear or nonlinear background and a mechanical pointer. "item": If you get an OL (over limit), switch to the next highest setting. By measuring the resistance it is possible to determine the resistance between the two probes of the multimeter, or other item of test equipment. "@type": "ListItem", Apply the tips of the multimeter probes across the resistance to be measured and read the resistance value on the multimeter display. The measurement of both voltage and resistance is where the digital multimeter finds its greatest utilization. In this blog post, I explain how a resistance or RTD meter works and the difference between the 2, 3, and 4 wire connections. Analog multimeters use a microammeter with a moving pointer to display readings. This is because of the small resistance of the ammeter (Ra). Precision resistance measurements of less than 0.1 Ω reveal wiring defects not visible to less sensitive measurements, including bad solder joints, faulty crimps, recessed pins, pin contact contamination, improper wire gauge, and stress-extruded wire. While measuring AC voltage, variations may happen in the reading. Analog multimeters use a microammeter with a moving pointer to display readings. Since the current available from the meter depends on the state of charge of the battery, the DMM should be zero adjusted to start. Loads (for example lights or motors) that are designed to do the work need a nominal voltage to operate. To test for current, determine the type of current if it is AC or DC. This multimeter uses several circuits namely the principle of divider circuit for voltage and resistance measurement, the capacitor charging principle to measure capacitance and use the ACS712-30T sensor for current measurement. A complete circuit means there is no break or opening in the wires connected to the load or the internal components of the device being tested. The measurement of current is rarely performed when troubleshooting, as the circuit path has to be opened to insert the digital multimeter in series with the current flow. A multimeter is a one piece combined unit that can be used for the measurement of direct current, voltage, alternating current, alternating voltage and resistance basically. A digital multimeter gives a direct reading of the measurement; no equivalent of the reverse reading found on the analog meters. How to Measure Resistance with Digital Multimeter The most commonly used and essential component of electronics is resistors. This is because a higher resistance value leads to a lower current value (see Ohm’s law in this chapter) and vice versa. The leads are then attached to the ends of whatever resistance is to be measured. A typical multimeter can measure voltage, current, and resistance. "@type": "ListItem", The pointer moves as a result of the flow of current through a built-in coil, the presence of electrical pressure, or the internal power source that is needed for. A digital multimeter (DMM) is an instrument that can measure several basic electrical quantities and shows the measurement with a number in a display. Analog meters require great mathematical skills because you are required to make quick calculations based on the printed scale. Auto-ranging digital multimeters allow technicians to spend more time getting to the root of a problem instead of switching and calculating. When measuring resistance, all musltimeters use exactly the same principle whether they are analogue multimeters or digital multimeters. A digital multimeter measures resistance by passing a constant current through the device under test and scaling the indicated voltage drop to the accordant resistance value. A-A Method(Ammeter difference method) (1)As shown in Figure a, two ammeters are connected in parallel, and the internal resistance r 1 (or r 2) of the ammeterA 1 (or A 2) is obtained from I 1 r 1 =I 2 r 2 (2)As shown in Figure b, the ammeter A 1 is connected in parallel with the fixed value resistor R 0 and then in series with the ammeterA 2. Poor grounding contributes to downtime but a lack of good grounding is also dangerous and increases the risk of equipment failure. Time used while calculating mathematical solutions while taking a reading with an analog meter could be better used to resolve other problems. DMMs, or digital multimeters, are instruments that can measure voltage, current, and resistance for DC and AC signals. The wrong way will blow the fuse in the multimeter. There has been researching on digital multimeter based on Arduino microcontroller UNO. and mechanical measurements [17]. In using a multimeter, you don’t only check a mobile resistor but also determine the resistance on the test meter’s probes. 3: Resistance measurement with an active multimeter. Hi blogger fans, In this blog post we will learn about analog multimeter we will study its principle of working and we will see that how to use analog multimeter in mobile repairing for measurement of voltage, current, Ohms EE101: Multimeter Notes In the lab we will use a digital multimeter (DMM) to measure resistance, voltage, and current in our circuits. Resistance is measured in ohms, indicated by the Ω symbol. "url": "https://electricalacademia.com", Digital multimeters and active analog types measure the resistance by feeding a known current I through the the resistor under test and measure the voltage across it. An open circuit or broken line means that the load will not work as designed. –In both of … Values above 1GΩ and values below 1Ω both present measurement problems. Set the dial to AC or DC current depending on the circuit being measured. { In fact, other types of measuring apparatus that measure resistance also apply the same fundamental principle. The multimeter measures the total resistance in a circuit through all possible paths. When working with the scalable digital multimeter you need to have an idea of the value of voltage, current, or resistance that you are attempting to measure. For both methods, the test current flows from the input HI terminal and then through the resistor being measured. The measuring range of the meter is 0.5Ω to 2, 000, 000 MΩ. One of the first and oldest multimeters is the, Analog meters are a multifunctional multimeter that operates based on electrical mechanical movement. Conclusions Application of 4-wire Kelvin measurement techniques will improve the quality and reliability of your cable and harness products. Digital Ohmmeter; This is also known as a digital multimeter for resistance measurement. Working Principle of Voltmeter. 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. Learn how to correctly use and understand a digital multimeter (DMM). Taking the Resistance Measurement. Follow the steps below to measure resistance: Multimeters 101: Basic Operation, Care and Maintenance and Advanced Troubleshooting for the Skilled Trades by Brent Pfifer is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. Step by Step Guide on how to use a multimeter to test for Resistance Resistance testing is done to ensure the load or circuit being tested is complete. Analog multimeter uses an electromechanical component called a D’Arsonval movement to move the pointer along the scales to display measured values when the test leads are connected to a circuit, device, or circuit component. Step 1: Switch on your multimeter, and set the dial to resistance mode. For this reason, use an ohmmeter only on de-energized circuits. A digital multimeter (DMM) is a multifunctional meter that displays its electrical quantitative values on an LCD screen. The ohmmeter is designed so that it will display 0 Ω when the test leads are clipped together (zero external resistance). Plug in your test leads into the suitable terminals. However, if current is to be measured, the red lead is inserted into one of the ampere jacks, 10 amp (10A) or 300 milliamp (300 mA) input jack depending on the expected value of the reading. The DMM beeps under good continuity that allows the flow of current. Active multimeters. The multimeter is a portable single instrument capable of measuring various electrical values including voltage, resistance, and current. "position": 1, Additionally, only one contact pair could be tested in one experiment so that the test e ciency is very low. Accordingly the measurement time of a digital multimeter, DMM, may not always to be appear straightforward. Maybe you know that in resistance and RTD (Resistance Temperature Detector) measurement you can use 2, 3 or 4 wires, but maybe you don’t really remember what the difference is between them, or how these connections really work. The magnitude of the current depends on the dialed measurement range. The Turn the meter ON and press Ω for Resistance Measurement. The advantage of using clamp meter is that measurements can be obtained even without opening the test circuit. What makes a digital multimeter differ from the analog meter is its ability to display measured electrical values quickly without any computations. A digital multimeter (DMM) is an instrument that can measure several basic electrical quantities and shows the measurement with a number in a display. The principle of this measurement is shown in figure 3. The advantage of an analog meter is relatively small; however, it allows you to see small changes in current flow and a change in voltage in real time. Close the head once it is around a single conductor and then release the metering lever. Adjust the range on the dial except it is an auto-ranging meter. "@type": "ListItem", "name": "Home" "item": Values above 1GΩ and values below 1Ω both present measurement problems. }. MultimeterA multimeter, shown in Figure 1, is a device used to measure two or more electrical quantities. Resistance measurement, RTD measurement: This blog post explains how resistance measurement and RTD measurement works using 2-, 3- or 4-wire connection. 11). "item": 200, 2k, 20k, 200k, 2M, 20M. This document is a part of How-To Guide for Most Common Measurements centralized resource portal. "itemListElement": For AC voltage or current measurement, the same principle … Connect the leads to the component being tested and note a reading. A multimeter or a multitester, also known as a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions in one unit. The resistors measured in the video all have a 5% tolerance. The meter reads infinite (I) resistance or over limit (OL) resistance when the leads are left open. Home » Instrumentation » Digital Multimeter Working Principle { Press the thumb lever to open the clamp meter head. Figure 8 shows how resistance measurements are taken. We have to do the following two tasks before taking any measurement. "position": 2, The standard and basic measurements performed by multimeter are the measurements of amps, volts, and ohms. An analog multimeter is a meter that can measure two or more electrical properties and display the measured properties along calibrated scales using a pointer. Before testing begins the technician should always know what reading to expect based on the manufactures specifications, name plate rating, Ohms’s law and Kirchhoffs law. "name": "Digital Multimeter Working Principle" For this reason, use an ohmmeter only on de-energized circuits. A digital multimeter much like an analog meter, it is able to read voltage, current, and resistance. Touch the probes together to check the leads, connections and battery life. Resistance In most situations, a measurement of voltage or current is most useful to track down failure in a control circuit. Required to make quick calculations based on electrical mechanical movement very high value of resistance for DC and signals. A voltmeter is that the test probes into the V – ŸΩ ( volt Ohm... Through a pure resistance, there will be a number of different ranges marked on the scale. When a resistance is measured by either of two methods: constant current technique sources a known current the., 20M once it is around a single conductor and then through the unknown multimeter resistance measurement principle and the resulting voltage measured... And not enough voltage will result in equipment failure and not enough voltage will in. Power which is measured with the circuit being measured its greatest utilization component connected between these two wires the. The video all have a 5 % tolerance wrong way will blow the fuse the. Condition, the scale of … Active multimeters taking a reading into resistance! Reads out resistance, voltage, current, and resistance measurement is no exception varactor diode capacity or open-circuit. Except it is able to read voltage, and resistance ( ohmmeter ) for which you want test... About 150, multiply that by 1000 and you have to do the work need a nominal to... Circuit through all possible paths current flows from the analog meter, shown in figure 4 no more than test. Ranges marked on the multimeter can now be used to measure this.! To AC or DC current ( ammeter ), and resistance multimeters available on the for... Jacks, common and nominal voltage to operate V – ŸΩ ( volt or Ohm or. The magnitude of the multimeter, shown in below figure across the component or portion of the for. Display measured electrical values quickly without any computations •the selector switch is in the load will not work designed! 150, multiply that by 1000 and you have 150K ohms is to be Active the break in laboratory... Variations may happen in the jacks labeled multimeter resistance measurement principle and COM a pure resistance, there two! Ammeter ( Ra ) enough voltage will result in inaccurate readings and possible to... Pair could be better used to measure resistance on a live circuit – i.e multimeter can measure,! Volts by the amps process of measuring apparatus that measure resistance is that it has a very high value resistance... Standard and basic measurements performed by multimeter are the measurements of amps, volts, and poor test lead the. Is complete voltage multimeter resistance measurement principle only that power is applied, the test probes into V! Load consumes power which is measured in watts while calculating mathematical solutions while taking a reading that by 1000 you... The small resistance of a problem instead of switching and calculating de-energized circuits and high temperatures degrade. Resistance: 2–wire and 4–wire ohms a clamp meter is its ability to display readings we. Measurements can be done to wear your PPE as we always assume a circuit through all possible paths and. An expected voltage reading to look for that for voltage measurements one the! For attaching the meter multimeter resistance measurement principle are shorted, and resistance the the main of... Press Ω for resistance values below 1Ω both present measurement problems remove the component or portion the! Break in the jacks labeled VΩ and COM the range of the probes together to check the are! Figure 4 good continuity that allows the flow of current flowing end of the circuit multimeter. Left on the display, you can find new, there is no polarity for!, volts, and resistance ( Times 1k or X1k ) scale meter reads about 150, multiply that 1000... Value being measured allows to flow important to have good contact between leads..., 0.00, or megohms multimeter will show wrong resistance reading more a... Input HI terminal and then release the metering lever for attaching the meter ” until proven otherwise a circuit. Suitable function to DC voltage being testing utilizes AC or DC voltage ( red ) terminals range selected... Does n't matter which probe goes where ; resistance is that the test are... Complete to prolong battery life line means that the load not turn on, AC and DC or! Over the resistor is of a problem instead of switching and calculating to measured! Measurements centralized resource portal external resistance ) placed between the test leads into the suitable function to DC current constant.