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Name: Due date: Grade:

ECE 2006 LABORATORY 1

DIGITAL MULTIMETER

Pre-lab Calculations: None

Objectives

The learning objectives for this laboratory are to give the student the ability to:

• use the digital multimeter (DMM) for resistance, voltage, and current measurements.

• determine circuit resistance from voltage and current measurements.

• determine digital meter accuracy from tolerance specifications.

• use the resistor color code chart.

• use tables for data.

References

1. D. E. Johnson, J. R. Johnson, J. L. Hilburn, and P. D. Scott, Electrical Circuit Analysis. 3rd Edition, Prentice-Hall, 1997.

2. Color Code Chart, available in Lab.

Background

Figures. Each figure must have a descriptive title and a number. Units must be included for all numerical values. Figures must be neat and easy to read and understand.

Data. Data is to be taken in ink. It must be clear as to what the data refers to. Do not forget units. The use of Tables is frequently convenient.

Tables. Tables are used to present information. They must be neat and easy to read and understand. Each Table requires a number for reference, a descriptive title, and column headings that describe the data. Units must also be included.

Sample calculations. Sample calculations are used to demonstrate how results were obtained. Label each sample calculation so that it is clear as to what it refers to. Each sample calculation should include a symbol equation, a set of numerical values, a result, and units, such as

R = V/I

= 10 volts/2 amps = 5 ohms

Tolerance. Accuracy is often expressed as a tolerance. A tolerance can be expressed as a percent or in original units. For example, a (2% tolerance on 50 volts could also be expressed as (1 volt.

Digital Multimeter Accuracy. This accuracy is on the bottom of the meter. It is given as a reading percent + number of least significant digits. For instance, if a meter reads 0.500 and has a tolerance of 3% = 2 digits, then its tolerance is

((0.15 = .002) = (.O17 = 3.4%

and the actual value is between .483 and .517. It is generally good lab practice to use the most accurate meter scale.

Division Tolerances. Assuming the tolerances are less than a few percent,

V ( V’ V V’ I’ V

------ = --- ( (--- + ---)---

I ( I’ I V I I

where V' and 1' are the tolerances on the original measurement and

V’ I’ V

(--- + ---)---

V I I

is the tolerance on V/I.

Equipment:

Digital Multimeter (DMM)

DC Power Supply

Resistor, 2200 (, 4700 (, 6800 (, 5%

Procedure

1. Individual resistors.

1.1 Color code chart. Use the color code chart to select three 5% resistor with nominal values of 2200 ohms, 4700 ohms, and 6800 ohms. Record these values in Table 1. Calculate the resistor's tolerance (5%) and minimum and maximum resistance, and record in Table 1.

1.2 Ohmmeter. Measure each of these 3 resistors using the DMM as an ohmmeter. Record these resistance measurements in Table 2. Calculate the meter's tolerance for this measurement and record in Table 2. Calculate the minimum and maximum circuit resistance for these ohmmeter measurements and record in Table 2.

1.3 Voltmeter and ammeter. Using the DMM as a voltmeter, adjust the DC power supply to approximately 10 volts. Record this voltage in Table 3. Calculate the meter's tolerance for this voltage and record in Table 3. Connect the circuit in Figure 1 for each resistor using the DMM as the ammeter (AM). Record the current in Table 3. Calculate the meter's tolerance for this current measurement and record in Table 3. From these voltage and current measurements and tolerances, calculate the circuit's resistance, the tolerance on this calculated resistance, and the minimum and maximum circuit resistance for these meter readings and record in Table 3.

2. Series Resistance Circuit.

2.1 Connect the circuit in Figure 2.

2.2 From the color code on the resistors, calculate the circuit's nominal equivalent resistance,

tolerance (5%), minimum and maximum circuit resistance and record in Table 1.

2.3 Measure the circuit's equivalent resistance using the DMM as an ohmmeter. Record this resistance measurement in Table 2. Calculate the meter's tolerance for this measurement and record in Table 2. Calculate the minimum and maximum circuit resistance for this ohmmeter measurements and record in Table 2.

2.4 Voltmeter and ammeter. Using the DMM as a voltmeter, adjust the DC power supply to approximately 10 volts. Record this voltage in Table 3. Calculate the meter's tolerance for this voltage and record in Table 3. Connect the circuit in Figure 1 substituting the series circuit in Figure 2 for R and using the DMM as the ammeter (AM). Record the current in Table 3. Calculate the meter's tolerance for this current measurement and record in Table 3. From these voltage and current measurements and tolerances, calculate the circuit's resistance, the tolerance on this calculated resistance, and the minimum and maximum circuit resistance for these meter readings and record in Table 3.

3. Parallel Resistance Circuit

3.1 Connect the circuit in Figure 3.

3.2 From the color code on the resistors, calculate the circuit's nominal equivalent resistance, tolerance (5%), minimum and maximum circuit resistance, and record in Table 1.

3.3 Measure the circuit's equivalent resistance using the DMM as an ohmmeter. Record this resistance measurement in Table 2. Calculate the meter's tolerance for this measurement and record in Table 2. Calculate the minimum and maximum circuit resistance for this ohmmeter measurements and record in Table 2.

3.4 Voltmeter and ammeter. Using the DMM as a voltmeter, adjust the DC power supply to approximately 10 volts. Record this voltage in Table 3. Calculate the meter's tolerance for this voltage and record in Table 3. Connect the circuit in Figure 1 substituting the parallel circuit in Figure 3 for R and using the DMM as the ammeter (AM). Record the current in Table 3. Calculate the meter's tolerance for this current measurement and record in Table 3. From these voltage and current measurements and tolerances, calculate the circuit's resistance, the tolerances, calculate the circuit's resistance, the tolerance on this calculated resistance, and the minimum and maximum circuit resistance for these meter readings and record in Table 3.

Conclusions

Which measurement technique is most accurate? (Answer in one or more complete sentences.)

[pic]

Figure 1. Current measurement

[pic]

Figure 2. Series circuit

[pic]

Figure 3. Parallel circuit

TABLE 1

RESISTANCE COLOR CODE

Resistance - ohms

|Nominal |( |Minimum |Maximum |

|2200 |110 | | |

|4700 | | | |

|6800 | | | |

| | | | |

| | | | |

TABLE 2

OHMMETER MEASUREMENT

Resistance – ohms

|Meter (Measured) |( |Minimum |Maximum |

|2200 ( ) | | | |

|4700 ( ) | | | |

|6800 ( ) | | | |

| | | | |

| | | | |

TABLE 3

RESISTANCE FROM VOLTAGE AND CURRENT MEASUREMENTS

|Voltage -v |Current-mA |Resistance - ohms |

|Meter |( |Meter |( |V/I |( |Min. |Max. |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

Sample calculations **show your tolerance calculations for the 4700( resistor**

TABLE 1 RESISTANCE COLOR CODE:

Nominal resistance = 4700(

Rtolerance ± =

Rmin =

Rmax =

TABLE 2 OHMMETER MEASUREMENTS:

Ohmmeter reading =

Rtolerance = (±)

Rmin =

Rmax =

TABLE 3 RESISTANCE FROM VOLTAGE AND CURRENT MEASUREMENTS:

Voltmeter (VM) reading =

VM tolerance ± =

Ammeter (AM) reading =

AM tolerance ± =

R = V/I =

Rtolerance ± =

Rmin =

Rmax =

................
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