### Lab 2 multimeter

• 1. INTRODUCTION A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter would include basic features such as the ability to measure voltage, current, andresistance. Analog multimeters use a microammeter whose pointer moves over a scale calibrated for all the different measurements that can be made. A multimeter can be a hand-held device useful for basic fault finding and field service work, or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems. Title : Analog multimeter and application Objectives : At the end of this experiment, student should be able to i. Do the measurement by using analog multimeter ii. Give knowledge about the usage of analog multimeter and its function. iii. Practice how to read the scale and set the range of multimeter Equipment List i. Analog Multimeter ii. Variable DC power supply iii. Bread board iv. Resistor v. Wire clip
• 2. THEORY Multimeter are very useful test instruments. There are two type of multimeter : Analog multimeter and digital multimeter. Analog meters use the force within the circuit to move a pointer to a scale position. Digital meters sense the force within the circuit and convert it to an ordinary number. By operating a multi-position switch on the meter they can be quickly and easily set to be a voltmeter, an ammeter or an ohmmeter. In other words, this instrument is used to measure resistance, current and voltage in electric circuit. It is also used to test electronic component such as resistor, capacitor, inductor, diode, transistor and etc. Besides, we can check the condition of these components whether good or not. If we looked at the analog multimeter, this equipment is classified into 6 basic division : a) Control unit Control unit can be set followed by measurement unit as we need. For Example, if we want to measured alternating voltage and current ( AU / AC ), we must set the control unit to AVC ( alternating current voltage ) and so on. b) Reading Scale Reading scale has several curve line with certain unit such as DCV.A, AVC,Ω and so on. Electric quantity is measured in this meter by the reading scale. c) Pointer The pointer is moving on the reading scale to show you the value of the electric quantity being measure.
• 3. d) Terminal Meter There ae two terminal meter named positive and negative terminal. Both of terminal are joint to test lead where as the red colour for positive terminal and black colour for negative. e) The pointer-zere adjustment ( only for analog multimeter ) It is used to set the scale of volt and current on zero. An adjustment is not required if the pointer is set to zero. f) The ohms-zero adjustment ( only for analog multimeter ) Along the bottom of the meter panel marked as ohms zero. This knob is used to set the full scale deflection of the pointer whenever the function is set to ohm. Full scale is usually zero ohms. To set this : I. Set function to ohms II. Set range to R × 1 III. Touch probes together Label of Each Indicator on the analog multimeter
• 4. Measurement method of analog multimeter Analog meters take a little power from the circuit under test to operte their pointer. They must have high sensitivity of at least 20 kΩ / V or they may upset the circuit under test and give an incorrect reading. Batteries inside the meter provide power for the resistance ranges, they will last several years but you should avoid leaving the meter set to a resistance range in case the lead touch accidentally and run the battery flat. Typical ranges for analog multimeters like the one illustrated in figure : 1.1 ( the voltage and current value given are the maximum reading on each range )  DC Voltage : 0.5V, 2.5V, 10V, 50V, 250V, 1000V.  AC Voltage : 10V, 50V, 250V, 1000V.  DC current : 50μA, 2.5mA, 25mA, 250mA. A high current range is often missing from this type of meter.  AC current : None. ( you are unlikely to need to measure this )  Resistance : 20Ω , 200Ω, 2kΩ, 20kΩ, 200kΩ These resistance value are in the middle of the scale for each range. If we looked at the reading scale of multimeter, we will see many colorful curve lines. Every line is used for certain unit such as resistance ( Ω ), direct voltage and current ( DCV.A ), alternating curret ( ACV ) and so on ( see figure 1.2 ).
• 5. Figure 1.2 A. Resistance Measurement The resistance scale on an analog multimeter is normally at the top, it is an usual scale because it reads backwards and is not linear ( evenly spaced ). This is unfortunate, but it is due to the way the meter works. 1. Set the meter to a suitable resistance range. Choose a range so that the resistance you expect will be near the middle of the scale. For example : with the scale shown below and an expected resistance of about 50 kΩ choose the × 1kΩ. 2. Hold the meter probes together and adjust the control on the front of the meter which is usually labeled “ 0Ω ADJ ’’ until the pointer reads zero (on the right remember ! ) If you can adjust it to read zero, the battery inside the meter needs replacing. 3. Put the probes across the component. Avoid touching more than one contact at a time or your resistance will upset the reading ! Choose scale range at × 1Ω. When the pointer shows at 20 scale reading, therefore the total of resistance is 26 × 1Ω = 26Ω