Experiment No. 1: Familiarization with Electrical Measuring Instruments1

Familiarization with Electrical Measuring Instruments

Ricardo D. Quintero Jr, Amilou Jane D. Suarez, Peter John Abel P. Tapitan, MIT

junjun_hapi777@yahoo.com.ph, malou15_jane14@yahoo.com.ph, peter_tapits@yahoo.com

Abstract– The purpose of this experiment is to help students familiarize with the common electric devices utilized in the laboratory. It aims to help students learn the proper connection of circuit trainer kit devices in creating electrical circuits. It also aims to demonstrate the characteristics and proper connection of the electrical measuring devices in order to enable students to analyze and determine several parameters(i.e., voltage, current, resistance) in a simple electric circuit.

Index Terms – circuit, current, voltage, power, resistance, galvanometer, Ohm’s Law, analog and digital multimeter, analog voltmeter and ammeter

I. INTRODUCTION

In the field of electrical and electronics engineering, study of electric circuits is so pervasive. As engineers, it is crucial that we know how to analyze systems containing several electric components. It is important to note that the experimental analysis of electric circuits requires the fabrication and measurement of several parameters (e.g., voltage, current, resistance). For this particular experiment, the students were introduced to some of the basic and electrical measuring instruments.

One of the instruments essential in the study of electric circuits is the voltmeter, ammeter and multimeter which usually combines several measurement functions in one unit. The typical multimeter is capable of measuring voltage, current and resistance. It can either be of analog or digital form. Digital

meters are widely used in experiments due to its efficiency and precision. Analog meters, on the other hand provide students an intuitive knowledge on the fundamental concepts of electric circuits.

Figure 1 (a) Digital multimeter, (b) Analog multimeter

The galvanometer, which is a type of an analog ammeter, is used to detect, measure, and determine the direction of small electric currents by means of mechanical effects produced by a current-carrying coil in a magnetic field. For this type of device, it is important to note that its current sensitivity (pointer deflection, d) is proportional to the amount of current in the coil (I M).

In analyzing basic electric circuits, it is important to have a basic knowledge in measuring parameters such as current, voltage and resistance. A voltmeter for example should be connected in parallel with the component to measure the voltage across it. Resistance is measured by connecting the test probes of the multimeter across the resistor. When measuring current, the ammeter should be connected in series with the component to measure the current through it. Figure 2 shows a

Experiment No. 1: Familiarization with Electrical Measuring Instruments2

comprehensive diagram for measuring the said parameters.

Figure 2 Schematic Diagram of a Simple Electric Circuit

Other apparatuses that we need to be accustomed with are the Circuit 1 trainer power supply and the Circuit 1 trainer kit comprised of several components like resistors, capacitors, transistors, jump wires, etc. The trainer kit also comes with a breadboard characterized by holes arranged in matrices which are used to construct temporary electric circuits. In creating a particular circuit, the terminals of the components are inserted into certain holes that may or may not be connected with one another.

Figure 3 (a) Breadboard mounted on a power supply, (b) Electrical components.

II. METHODOLOGY

The first and second part of the experiment dealt with identifying and analyzing the characteristics of an analog ammeter and an analog voltmeter by means of measuring their respective resistances.

The third part of the experiment involved creating and analyzing the characteristics of the simple electric circuit shown in the figure.

Figure 4

For each particular resistor used in the circuit, the voltage, current and resistance were identified and recorded. The power consumed

was determined using the equation: PL=V L I L.

10 trials were conducted with each trial utilizing a different type of resistor. The data gathered were then used to solve for the following formulas:

Formula 1: V L

I L

Formula 2: PL

I L

;

Formula 3: V L

2

PL

III. RESULTS

This experiment was divided into three parts, the first two parts is about determining the characteristics of the two commonly use electrical measuring devices, the analog ammeter and the analog voltmeter.

Table 1. Characteristics of Analog AmmeterRT (input resistance) VM = ITRT

0.2Ω 60mV

From the results of part A of the experiment which is about determining the characteristics of analog ammeter, refer to Table 1, we determined the RT (input resistance of the ammeter) and the Vm (voltage that will cause full scale deflection). In this part, VOM was really

Experiment No. 1: Familiarization with Electrical Measuring Instruments3

useful because we use it obtain these data. The data shows small amount of input resistance, since ammeter is use to measure currents, small amount of input resistance allows the flow of larger currents.

Table 2. Characteristics of Analog VoltmeterRT

(input resistance)

I m=V T /RT VoltmeterSensitivity

6.05kΩ 0.5 mA 2.02kΩ/V

Referring to table 2, showing the results of part B of the experiment, you can see that the input resistance for analog voltmeter is very much larger than the input resistance of a analog ammeter. The input resistance of the voltmeter here was obtained from measuring it across the input terminals by means of the VOM. From the measured input resistance, we determine the Im

by dividing it to the full scale reading of the voltmeter. The voltmeter we use has sensitivity 2.02K ohms per volt, which is the reciprocal of Im .

Table 3. Measured Data (Part C)Trials V L I L P L Given R

L

1 19.99V 0.06A 1.2W 325.6Ω2 19.99V 0.04A 0.8W 463Ω3 20V 0.03A 0.6W 677Ω4 20V 0.02A 0.4W 987Ω5 20V 9.18mA 0.18W 2177Ω6 20V 4.3mA 0.086W 4660Ω7 19.99V 2mA 0.04W 9830Ω8 20V 0.92mA 0.02W 21.66KΩ9 19.99V 0.41mA 8.6mW 46.5KΩ10 20V 0.02mA 0.4mW 0.974MΩ

Table 4. Continuation of table 3Trials VL/IL PL/IL

2 VL2/PL

1 333.13Ω 333.17Ω 333.33Ω2 499.75Ω 500Ω 499.5Ω3 666.67Ω 666.6Ω 666.66Ω4 1000Ω 1000Ω 1000Ω5 2178.65Ω 2178.65Ω 2178.65Ω6 4651.16Ω 4651.16Ω 4651.16Ω7 9995Ω 10000Ω 9990Ω

8 21739.13Ω 23629.99Ω 20000Ω9 48756.10Ω 51160.02Ω 46465.13Ω10 1MΩ 1MΩ 1MΩ

Using the given circuit in figure 4, we have taken results by having different values of resistor, as shown in table 3 and 4. This is the last part of the experiment and considered to be the important part. The proper use of the measuring device is important to obtain accurate results in this part, also the correct use of other electrical components.

In table 3, you can observe that when the value of the resistor is larger, the value of current is lower. This means that resistance is inversely proportional to current. To test the data we gathered, we determine the value of the resistor using 3 different formulas, as shown in table 4, and from these results, you can see that it has small difference from the given resistor, this may means that the resistors are in good conditions and the date we gathered was reliable.

IV. CONCLUSION

In this experiment we determined the characteristics and proper connection of common electrical measuring devices, we read measurements of basic electrical measuring device and we familiarized ourselves with the basic circuit training kit and learned the proper connection of trainer kit devices.

Practically all electric measurements involve either the measurement or detection of electric current. The measurement of electric current can be accomplished by means of any one of the three principal effects of current: heating effect, chemical effect, or magnetic effect. The galvanometer sensitivity exists although there are numerous ways of expressing it; current sensitivity, voltage sensitivity, and mega ohm sensitivity, each involving a statement of the electrical conditions necessary to produce a standard deflection. In our experiment we only determine the characteristic of ammeter and voltmeter and from there we have the current sensitivity as current per unit deflection (k=I M /d), voltage sensitivity, and

Experiment No. 1: Familiarization with Electrical Measuring Instruments4

voltmeter sensitivity as the voltage required per unit deflection.

In the last part of the experiment, the experiment shows the importance of the correct use of the circuit 1 trainer kit, electronic devices. This also shows the relationship between voltage, current and resistance, and somehow also proves the ohm’s law which states that the voltage across the resistor is directly proportional to the current flowing through the resistor [1]. We can also test the electrical components if they are in good terms using the electrical measuring devices. We have also learned that when measuring voltages and currents, the voltmeter must be connected in parallel across the circuit element so that its inclusion in the circuit has negligible effect on total resistance and current flowing in the circuit while the ammeter must be connected in series with the circuit element.

REFERENCES

[1] C.K. Alexander and M.N.O. Sadiku, Fundamentals of Electric Circuits, 3rd

Edition. New York: McGraw-Hill, 2007

[2] R. Nave, Ammeter Design, http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/ammet.html

[3] Young, Freedman, University Physics with Modern Physics, 11th Edition, Pearson Education Inc., 2004

[4] Multimeter. (n.d.) In Sci-Tech EncyclopediaRetrieved from http://www.answers.com/topic/multimeter

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