Experiment I
Simple Voltage and Current Measurement
Objective
The objective of this experiment was to measure the Voltage and Current. Upon completion of this experiment I was able to:
1) Set the DC power supply to a specific voltage.
2) Properly connect the voltmeter to measure voltage.
3) Measure current with the ammeter.
4) Measure resistance with the ohmmeter.
5) Determine the accuracy of a given meter reading.
Theory
The theory required for this experiment was an understanding of Ohm’s Law. Ohm’s Law is the algebraic relationship between voltage and current for a resistor. Resistance is the capacity of materials to impede the flow of current or electric charge. Ohm’s Law expresses the voltage as a function of the current. It was also necessary that the concept of measurement accuracy be understood. This is discussed below.
Accuracy is of primary importance in an experimental work. The tolerance quoted by the meter manufacturer allows us to calculate the accuracy of any reading taken with that particular meter. For example, assume that the dc voltage scale on a particular multimeter is rated at ± 3% of full scale. This means that a reading on the 10V scale is accurate to (± 0.03%)(10) = ± 0.3V. Thus, a reading of 9V on the10V scale indicates a true voltage, which lies between 8.7 and 9.3 V. A reading of 1V on the scale would indicate a true voltage between 0.7 and 1.3 V. At this point, the error is ± 30%! Any reading less than 10% of full scale should be viewed with suspicion since most meters are very inaccurate n this range.
Circuit Diagrams
For this experiment we used a Power supply source, voltmeter/ammeter/ohmmeter.
Fig 1.1 Power Supply and voltmeter in parallel
Power Supply Voltmeter
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Fig 1.2 Simple voltage measurement circuit.
a a
b a b a a d c c d
c d
Fig 1.3 Simple current measurement circuit
Power Supply
(Be sure current I control is at maximum setting)
Fig 1.4 Circuit to measure resistance
Procedure
To measure the voltage output of the power supply, we connected the voltmeter as shown in Fig. 1.1. We made sure that the voltmeter is always connected in parallel with the voltage being measured. Before turning on the power, we set the voltmeter voltage range to a DC value higher than the highest voltage we expected to measure. This precaution must be observed with all meters in order to avoid the possibility of burning out an expensive instrument.
We then set the current control to maximum current and adjust the output voltage of the supply to values of 2.5, 10, and 15.
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