Multimeter lab

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Lone Star College System, North Harris *

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2426

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Electrical Engineering

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Apr 3, 2024

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pdf

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Name: | V(' \ \ Date: 2 [Z ) lzml’l Introduction to the Multimeter (DMM) (19 pts) Part L. The digital multimeter (DMM) can be used to measure Voltage (V), Current (/), and Resistance (R), as well as a few other quantities depending the make and model of your DMM. It combines a Voltmeter, Ammeter, and Ohmmeter into one handheld device. The front of the DMM consists of a liquid crystal display (LCD), some push buttons (optional), a dial to select the scale and quantity to be measured, and three or four connection sockets — one black common ground (COM), one red for measuring voltage (V) and resistance (Q), and two yellow sockets for measuring current, one for small currents (mA, pA) and one for larger currents (10 A). The Amprobe 33XR-A model (Figure 1) can also be used to measure Capacitance and Temperature and to test Diodes. The dial is divided into sections and each section is subdivided into scale settings. For voltage and current there are 2 separate sections for alternating current (AC represented by the letter with a tilde ~ on top similar to a sine wave) and direct current (DC represented by a solid and dashed line == on top). Figure 1 Amprobe 33XR- A. Measuring and reading Voltage: Vab Plug the black lead to the COM (common ground) socket and the red lead to the V socket. Use the dial to select ¥ (DC volts) or ¥ (AC volts) and the appropriate scale. Remember that we are measuring the potential (or voltage) difference across a circuit element so we must connect the DMM in parallel with the element, as shown schematically in Figure 2. If the leads are reversed, you will a b read a negative voltage (potential difference AV = V2—V1). Figure 2 Measuring voltage The scale setting gives the maximum value that can be read. For example, if you set the dial to 4, the meter will read voltages up to 4 V. If you try to measure a 9 V battery on this setting the meter will read OL (over the limit). The next available setting on this model is 40 V. Note that you will get the most precise reading (smaller decimal place) when you select the lowest possible setting, without exceeding the maximum. For example, if you had the dial set to 400 V and it read 28.9 V, you can set the dial down to 40 V and it will read 28.85 V. This reading is more precise than the previous one, and too large for the 4 V setting. B. Measuring and reading Resistance: For resistance readings on this DMM the wire leads are connected to the same sockets as for voltage readings. However, we need rotate the dial to read Resistance (Q) and choose the appropriate scale. As before, select the highest setting to start, which it this case is 4M (M means “mega” or 10%). We measure resistance across a circuit element, so we connect the DMM in parallel with the circuit element of choice as in Figure 3. Example: The LCD reads 0.000 M. That means the resistance is too low to register on this setting, so we dial down to 40k and read 0.328 kQ, which means that R =0.328 x 10° Q = Figure 3 Meosuring 328 Q. We note that we can dial it down to the 400 Q setting. Now it reads 327.9 Q. Voltage and B - oy ] : i e Again, we gained precision (tenths of a volt) by choosing the lowest setting. Note that to measure the resistance of any circuit element, the circuit should be de-energized, and the element should be removed. Never try to measure resistance on a live circuit

C. Measuring and reading Current: ((Lep ) To measure current on this DMM (and most others), you may first have to ~ disconnect and reconnect the leads on DMM. Current must be read in series with the circuit element because we measure the current flowing through it. Therefore, we must break the circuit and connect one lead to each side of the open circuit so the current flows through the DMM. Be sure to disconnect the power source BEFORE disconnecting anything. After the leads are properly connected, reconnect the power source to read the current. Current can be read before or after the element. To read the current through resistor Rs, to connect the DMM as shown in Figure 4. Figure 4 Meosuring current. Note: any place in a circuit that has 3 or more wires connected is called a junction. Current will divide into the multiple paths inversely proportional to the resistances. At any junction, conservation of charge demands that the total current flowing into any junction must be equal to the total current flowing out. Just like water flowing through pipes. This is known as Kirchhoff’s Junction Rule. Part I1. Rewrite the following metric prefixes in terms of the power of ten (i.e. kQ =10 Q) (6 pts; tmv=_\Q " sow=_ 10" W 2.Mo=_\Q" 1) 5.nC =__\( . ( 3.uA = Q A 6. kI = §(ﬂ ) Part I11. Multiple choice quiz (1 pt each = 6 pts): 1. The voltmeter in Figure 5 will measure the potential difference across: a. Ry @)RI and Rz b.R2 e.Rzand R3 c.Rs f.Ri, Ry, and R3 2. The ammeter Figure 6 will measure the current through: @R d.Riand R b. Rz e. Rz and R3 c.Rs f. R1, Rz, and R3 Figure 6 b4

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