How to Use a Digital Multimeter - Coursework Example

Table of Contents Table of Contents 2 4 Introduction 5 Purpose 5 Scope 5 Limitations 6 Graphics and symbols 6 Section one: 6 1 How was thedata gathered? 6 1.2 Comparison between the analogue multimeter and digital multimeter 7 Section two: 8 Functions of multimeter buttons 8 Section three: 11 How to perform the different functions of multimeter 11 Written Analysis 13 Written Statement 14 Concluding statement 15 References 17 Glossary 17 Appendix 19 Table of Figures Figure 1: Analogue Multimeter (Alibaba 1999-2013) 7 Figure 2: Digital Multimeter 7 Figure 3: Digital Multimeter 8 Figure 4: Symbol for voltmeter 9 Figure 5: Symbol for Ammeter 9 Figure 6: Symbol of ohmmeter 9 Figure 7: Measuring Voltage 11 Figure 8: Probes of a multimeter 11 Figure 9: Measuring Ammeter 12 Figure 10: Measuring resistance 13 Abstract A digital multimeter is a device that can be used to measure current, voltage and resistance among various devices in a circuit. Its effective and efficient use requires a thorough understanding of key concepts of electricity, and that is what this document serves. It explains the key terms that are used while working with the multimeter, how to connect the multimeter to various components to take various measurements, precautions to take while using the device and the device limitations. The guide gives and illustrates briefly an overview of most of the symbols used to make circuit diagrams and their meaning. A glossary at the end of the document gives an alphabetical list of an overview of the abbreviations and terms used in the guide. Introduction Purpose The main purpose of this document is to guide users on how to effectively and efficiently use a digital multimeter. Graphics and symbols are used to illustrate key concepts of the guide. A multimeter is a measuring device that is used to measure current, potential difference and resistance. All these functionalities have specific devices for measuring them but a multimeter combines them on a single device. A knob on the multimeter is used to change between these functions. The multimeter is usually used in areas involving DC and AC currents. In this guide, only DC circuits have been put into consideration but key observations about AC counterparts have been mentioned. The main advantage of using digital multimeter as compared to analogue ones is that they are easier to read which reduces interpolation errors and they are more accurate. They are important in circuits and components measuring, testing, troubleshooting and repair. Scope Digital multimeter varies in size, price and capabilities. Size ranges from small hand-held to large ones. Hand-held devices operate on a battery that must be replaced periodically. Large multimeters operate on AC voltages hence there are more accurate but are quite expensive. This user guide will put into focus the hand-held multimeters since they are readily available and can be easily used to demonstrate major capabilities of the device. This guide illustrates how the multimeter measures voltage, current and resistance. Other aspects such as continuity, frequency and capacitance can also be tested but will not be described in this guide. The appendix which is written at the end of the document gives key references which can be used by the user to get the details. Limitations Digital multimeters are limited in various ways during operation: 1- They operate on battery power which when low can hinder the performance of the device. This can lead to wrong values being read and the LCD screen being dim. 2- The multimeter is limited in voltage. If increased beyond this limit, the device may be damaged. 3- Testing diodes using digital multimeters can be tricky, because the health of a diode is usually indicated by a range between 0.6 and 0.7 that may not be on the multimeter in question. 4- To measure the frequency in a circuit would involve measuring the voltage and also recording time to enable calculation of frequency. Graphics and symbols Section one: 1.1 How was the data gathered? The data was collected and gathered by taking measurements of a variety of electronic components such as a resistor, capacitor and a battery. 1.2 Comparison between the analogue multimeter and digital multimeter Figure 1: Analogue Multimeter (Alibaba 1999-2013) An analogue multimeter has a moving coil element. It has several ranges that are used to measure different quantities. Switching between the various ranges is done by the use of a rotary selector switch. Some sample ranges include: Current :0-1 A 0-5A Voltage: 0-10V 0-150V Resistance: 0-10 Ω Figure 2: Digital Multimeter A digital multimeter on the other hand has an LCD screen for displaying results and a function selector knob. The range is determined by the multimeter automatically. Input terminals are used for the measurement of voltage, resistance and capacitance. (Analogue and Digital Multimeters, 2012). Section two: Functions of multimeter buttons A digital multimeter has a single knob and three input terminals as shown in the image below. Figure 3: Digital Multimeter The knob is used to select among the various functionalities of the device. The terminals are connected to the two probes that are attached to the circuit or component being measured. 1: Basic features All multimeter are provided with the following meters: 1.1 Voltmeter for voltage: Figure 4: Symbol for voltmeter Voltmeter-A measuring device used to measure the potential difference between two points in a circuit. This voltage could either be DC or AC voltage in a circuit. 1.2 Ammeter for current: Figure 5: Symbol for Ammeter Ammeter-A measuring device used to measure the current in a circuit. DC current is current from a source like a battery.AC means alternating current and this is the current from the mains supply. 1.3 Ohmmeter for resistance: Figure 6: Symbol of ohmmeter Ohmmeter-A measuring device that is used to measure the resistence through a component. 2: Additional features Depending on the digital multimeter in question, additional features are included such as Capacitance meter: For measuring capacitance in capacitors Inductance meter: This is mainly combined within an LCR meters. L for inductance, C for capacitance and R for Resistance. Frequency meter: This is a meter for measuring frequency of AC voltages. It’s calibrated in Hertz (Hz). Diode meter: Tests diodes. This meter normally tests the resistance of the diode in both forward and reverse direction. Section three: How to perform the different functions of multimeter 1: How to measure voltage: Voltage is the potential difference between two points in a circuit. It’s given in volts (V) and is usually measured using a voltmeter. In order to determine the voltage of a component as follows: 1- First determine whether the component uses DC or AC voltage. Caution must be taken in testing this, as it could damage the meter. 2- Set the knob on the multimeter such that the notch on the knob lies on the voltage (V) section. Figure 7: Measuring Voltage 1- 2- Make sure to connect the meter in parallel to the circuit. 3- Connect the two probes to the device to measure voltage. Figure 8: Probes of a multimeter 4- The voltage measurement will be indicated on the LCD screen of the multimeter. 2: How to measure current Current refers to the flow of charges through a conductor in a circuit. Charges usually move from the positive node of a battery in DC current to the negative node. Current is measured using a device known as an ammeter and is usually given in amperes (A). Measuring current using a multimeter as follows: 1- Determine whether the circuit is DC or AC 2- Adjust the knob on the multimeter such that its notch is on the current section. Figure 9: Measuring Ammeter 3- Connect the multimeter probes to the circuit in series. Current passes through the multimeter without being altered since the multimeter has a very low resistance. In this setup the multimeter acts like an ammeter and displays the current reading on the screen in Amperes (A). 3: How to measure resistance Resistance is the hindrance to the flow of charges in a circuit. As charges flow in a conductor, molecules in the conductor interfere with the flow. Resistance is given in Ohms and is measured using a device known as an Ohmmeter. To measure resistance using a multimeter as follows: 1- Power off the circuit and remove the component. 2- Adjust the knob on the multimeter such that its notch is on the resistance section. Figure 10: Measuring resistance 3- Connect the in series to that component and get the reading. Multimeter measure the resistance by passing current through the component and determining the voltage produced. The multimeter should not be connected to the circuit while the power supply is on as it may be damaged. Written Analysis The user guide was tested by two students undertaking a course in engineering. The purpose was to figure out how the guide will fair in a real life situation. The following issues were observed by the students: 1. Wrong connection of the multimeter to circuits led to wrong results. 2. Short circuits in the connection posed a great problem. After analysis the circuit, the users recommended: 1. The guide should clearly indicate how to properly connect the meter to avoid making connection errors. 2. The guide to include some of the precautions to be taken while undertaking the experiment. With the above feedback in mind, the guide was reviewed and diagrams added to make it clearer. The guide also highlighted some of the key precautions that users should take to avoid damage to the meter, injuring themselves and damaging the electrical components being tested. Testing the guide practically was of great essence as it helped identify the key challenges users experience while working with the multimeter and making recommendations and reflecting the concerns on the guide. The experiment can be used on a greater scale by allowing it to be used by the people in the fields of engineering and electricity. This will also allow a more thorough and more challenging test of the guide because of the different scenarios. Written Statement The purpose of this guide was illustrating the use of a digital multimeter, precautions and a comparison of a digital multimeter with an analogue one. The guide also discussed the typical working of a switched range multimeter, where the range of the device is selected before testing the component (Philips, 1999). The other version of a digital multimeter is the auto ranging multimeter. In this, the user selects between AC and DC values. After switching to this, the multimeter adjusts the range automatically in order indicate a meaningful reading. This kind of multimeter is expensive compared to the switched range multimeter but it’s much easier to use. It was not available for testing and illustration purposes. Safety reasons dictate that the multimeter should not be connected to the AC power source. Batteries should be properly disposed after use to avoid them causing harm to people. Other proper precautions should be taken while working with the digital multimeter and other electrical components. Concluding statement Digital multimeter plays a handy device that assists technicians in troubleshooting and testing electrical installations. It combines the ability to measure current, voltage, resistance, connectivity and capacitance on a single device. The functionality of the multimeter can be adjusted by use of a single knob found on the multimeter. The knob also helps in determining the range to be measured by the multimeter. The measurements of the multimeter are given on an LCD screen on the device usually to the specified precision. To measure a given quantity, the device is appropriately connected as above discussed and then the range can be adjusted to give a better precision of the results. This is usually the case with switched range multimeters that have their ranges adjusted manually. The other version is the auto ranging multimeter that is able to automatically adjust the range to reasonable ranges. This guide has explained how the various quantities can be measured and some of the precautions to be taken while measuring. Effective and efficient use of the digital multimeter is a key requirement for engineers that have to be observed. Digital multimeter is one of the tools required by engineers in their day to day working making the understanding of their operation a fundamental requirement. References Access Communications Pty Ltd. (2011). Power Supply Units Abbreviations. Retrieved from Access Communications Pty Ltd: http://www.accesscomms.com.au/reference/polarity.htm Gregorec, J. (2003, Jan 1). How to use Digital Meters. Retrieved from Electrical Construction and Maintenance Magazine: http://ecmweb.com/basics/how-use-digital-multimeters Philips, W. (1999). Using a multimeter. Retrieved from Design Electronics: http://www.doctronics.co.uk/meter.htm#measure Glossary AC-Alternating Current-This is current from the mains electricity. Ammeter- a device used to measure current Ampere-SI unit for current DC-Direct Current-Current from a steady voltage source e.g. battery Meter-A device used to measure some given quantity. Ohmmeter-Device used to measure resistance of component. Ohms- Units for giving the resistance of a component Voltmeter – device used to measure the potential difference in a circuit. Volt- Unit used to express voltage in a component or circuit. Appendix Below is a list of some useful resources that have been mentioned in this guide that can be used to gather more information about digital multimeters. 1. Switched range and auto ranging multimeters. http://www.doctronics.co.uk/meter.htm#measure 2. Measuring capacitance, frequency and continuity in circuits using digital multimeters http://ecmweb.com/basics/how-use-digital-multimeters 3. Instructions for Digital Multimeters http://www.ehow.com/way_5562917_instructions-digital-multimeters.html Below are a number of symbols that will be used in this document and their meaning. Symbol Description Resistor-this is an electrical device that hinders the flow of current. Voltmeter-A measuring device used to measure the potential difference between two points in a circuit. Ohmmeter-A measuring device that is used to measure the resistence through a component. AC/DC source-This could be a battery or a wall socket Direct Current-This is current generated by a battery Connecting Wires-This are the conductors connecting components in a circuit. Ammeter-A measuring device used to measure the current in a circuit. Read More