DE LA SALLE UNIVERSITY - DASMARINAS COLLEGE OF ENGINEERING, ARCHITECTURE AND TECHNOLOGY ENGINEERING DEPARTMENT
EXPERIMENT NO. _6_
TITLE: DC POWER MEASUREMENT
DOMINGO, KENNETH S. EEE31 GROUP NO.: __ DATE PERFORMED: 02 SEPTEMBER 2011 DATE SUBMITTED: 16 SEPTEMBER 2011
ENGR. ROBERT J. SUPNET INSTRUCTOR
Table 6 – Final Data Sheet Experiment No. 6 DC Power Measurements
Name: DOMINGO, KENNETH S.
Date Performed: 02 SEPTEMBER 2011
Section/Yr.: EEE31
Instructor: ENGR. ROBERT J. SUPNET
Part
Trials
VT
A
I-Fig.5.1
1
9.98V
2
I-Fig.5.2
VR
PR
R
6.2mA
61.88mW
16.1 Ω
9.98V
98.2mA
980.04mW
98.4Ω
1
9.98V
6.2mA
9.98V
61.26mW
16.1 Ω
2
9.98V
98.2mA
9.98V
987.07mW
98.4Ω
SAMPLE COMPUTATIONS
SPECIFICATIONS OF APPARATUS AND INSTRUMENTS:
DC Source Model: GW Instek GPC 3030DQ Power Supply The GPC SERIES have dual adjustable outputs plus a single 5V 3A fixed output. The dual adjustable outputs can be operated independently, in series, or in parallel. Features: •
Dual Adjustable Output plus 5V 3A Fixed Output
•
Auto Tracking
•
Auto Series and Parallel Operation
•
Constant Voltage and Constant Current Operation
•
Low Ripple and Noise
•
Internal Select for Continuous or Dynamic Load
•
Overload and Reverse Polarity Protection
•
Two 3½ Digit 0.5" LED Displays Switchable Between Voltage and Current
•
Model GPC-3030DQ has Four Separate Displays for Simultaneous Voltage and Current Readings
Multitester (VOM) Model: GW Instek GDP 391A Multimeter Features: •
Multi
Function:
AC/DC
Voltage,
AC/DC
Capacitance and Frequency Measurement •
Audible Continuity Check and Diode Test
•
3¾ Digit, 3999 Counts
•
Auto/Manual Ranging
•
40 Segment Analogue Bar Graph
•
Data Hold
•
Max/Min Memory
•
Relative Mode
•
High Energy Fused for 10A Range
•
Auto Power Off
•
Optional Holster Available
Rheostat Range: 0Ω to 100Ω
Ammeter Quantity: Four Range: 0-200mA, 0-5mA, 0-20mA, 0-50mA Connecting Wires Quantity: Ten
Current,
Resistance,
Type: Banana Plug/Connector Rheostat Range: 0Ω to 100Ω Wattmeter
Model: Handheld Digital Watt Mater DWM-03060 General Specifications Display
0.5" LCD ( Liquid Crystal Display ), Max. indication 1999.
Measurement
Watt ( true power ), DCV, ACV, DCA, ACA.
Polarity
Bipolar by automatic Switching , " - " indicates reverse polarity.
Zero Adjust
Watt : External adjustment for zero of the display, limited to +30 to -30 digits. ACV/DCV, ACA/DCA : Automatic adjustment.
Over-input
Indication of "1" or "-1".
Operating Temp.
0° C to 50° C ( 32° F to 122° F ).
Operating Humidity
Less than 80% RH.
Power supply
006P DC 9V battery. (Heavy duty or alkaline battery)
Power Consumption
Approx. DC 6 mA
Weight
500g (including battery)
Standard Accessories
Test lead....................1Pair Instruction Manual.......1PC
2-2 Electrical Specifications ( 23°± 5° C ) DC VOLTAGE Range
Accuracy
Resolution
Overload Circuit Protection
200 V
±(0.8%+1d) 0.1 V
ACV : 600 ACV
600 V
±(0.8%+1d) 1 V
DCV : 600 DCV
Remark : *Input Impedance :1 Mega ohm DC CURRENT Range
Accuracy
Resolution
10 A
±(1% + 1d) 10mA
Max. Input Current 10 A
Remark : *Voltage drop ( in case of full scale ) : 200 DC mV
PICTORIAL DIAGRAM
DISCUSSION
Power is the rate at which energy is converted. Power may also be defined as the rate of doing work. (Schuler and Fowler, 1993: 54) Power is often used in conjunction with the word dissipation. Power dissipation usually refers to the rate at which electric energy is converted to heat energy. A resistor in an active circuit may feel the warm to the touch. This is due to the conversion of electric energy. The resistor dissipates the heat energy by transferring it to the surrounding structures and to the atmosphere. It takes time to transfer (dissipate) the heat energy. High power means a rapid conversion of electric energy to heat energy, and the resistor will reach a high temperature. (Schuler and Fowler, 1993: 57) Direct current power is usually measured by means of a voltmeter and an ammeter. Since the power is the product of volts and amperes (P=VI), it is merely necessary to multiply the volts by the amperes to obtain the power in watts. (Dawes, 1975: 189) A wattmeter is a device which measures the average power that is delivered to a load. It contains a rotating high-resistance voltage, or potential, coil, connected in parallel with the load and a fixed low-resistance current coil which is connected in series with the load. The device has four terminals, a pair to accommodate each coil. A typical connection is shown in the figure.
We see that the current coil responds to the load current, whereas the voltage coil responds to the load voltage.
One terminal each of the coils is marked ± so that if the current enters the ± terminal of the current coil and the ± terminal of the voltage coil is positive with respect to its terminal, then the meter gives a positive, or upscale, reading. In the figure, this corresponds to the load absorbing power. If the terminal connections of either current coil or voltage coil (but not bith) are reversed, a negative or downscale, reading is indicated. Most meters cannot read downscale – the pointer simply rests on the downscale stop. Thus such a reading requires reversing the connections of one of the coils, usually the voltage coil. Reversing connections of both coils does not affect the reading. (Johnson, Hillburn and Johnson, 1990: 392-393) Furthermore, difference,
often
a voltmeter is referred
to
as
a
device
"voltage".
for It
measuring must
be
potential connected
in parallel with the element in question so that the potential difference across the voltmeter is the same as the potential difference across the element being measured. The + side of the voltmeter is connected to the high potential side of the element. The voltmeter must have a high resistance so that it does not divert a significant amount of current from the element being measured.
An ammeter is a device for measuring the current flowing through an element in the circuit. In order that all the current flowing through the element also flows through the ammeter, it must be connected in series. It
must have a low resistance so that it does not impede the flow of current. It is connected such that the current flows from the + to the - side of the meter.
INTERPRETATION/ANALYSIS OF RESULTS
Based on the data that have been recorded, upon the trial 1(I-Fig 5.1) the current that was recorded is just as low as 6.2mA and the total voltage that was recorded is about 9.98V resulting to a low power which is just 61.88mW. Upon the trial 2(I-Fig 5.1) the current that was recorded is high which is 98.2mA and the total voltage that was recorded is about 9.98V resulting to a high power which is just 980.04mW.
These results only show that the power is directly proportional to the product of the current and voltage. Furthermore since the resistance is inversely proportional to current but directly proportional to voltage. The power can also be represented in terms of resistance and voltage or resistance and current (P=V2 /R; P=I2R) which shows inverse and direct square relationship upon the power to voltage and current individually.
The experiment that was conducted is consisting of two parts namely the Ammeter-Voltmeter Method (part I) and Wattmeter Method (part II)
each with two trials. The ammeter-voltmeter method uses the relationship of power into two parameters which are voltage and current, whereby can be measured by voltmeter and ammeter, which is this method was named after.
Unfortunately we was not able to conduct the wattmeter method because of the malfunctioning wattmeter, so we was not able to compare those two aforementioned methodologies.
REMARKS AND CONCLUSION
Therefore
I
conclude
that the
electrical DC power is
directly
proportional to the product of current and voltage, exclusively if the power to be considered is a power in a resistor component which has a time-invariant voltage and current ratio, likewise in this experiment. This theorem was again proved upon this experiment which has two trials, which limits the possible errors.
Furthermore we was able to employ this theorem into a certain method of DC power measurement which is the ammeter-voltmeter method and being proved upon two trials that this method is merely accurate.
ANSWERS TO QUESTIONS AND PROBLEM
1. Compare the movement of the voltmeter with that of the ammeter. In what important respect does the voltmeter differ from the ammeter? How is the current in the coil of a voltmeter limited when the voltmeter we connected across the line? 2. What instruments are generally used in measuring power in a DC circuit? Show that these instruments themselves take power. What should be the relative positions of the voltmeter and ammeter when power delivered to a low resistance is being measured? Show the methods by means of which correction for power taken by the instruments being made? 3. Describe the construction of a wattmeter, and show the principle of its operation. In what way do the fixed and moving coils differ in construction? In their manner in connecting to the circuit? Why are the instrument deflections a function of power? What care is necessary in using this type of instruments with direct current?
An instrument for measuring the power of an electrical current in watts. The most common wattmeters are the dynamometer type, in which the mechanism consists of an immovable coil connected in series to a load (the current circuit) and then to a movable coil, which is connected through a large auxiliary resistor (the resistor circuit) parallel to the load. The operation of the dynamometer wattmeter is based on the interaction of the magnetic fields of the movable and fixed coils as an electrical current passes through them. In the case of direct current the torque, which causes a deviation in the movable part of the device and in the needle (indicator) connected to the device, is proportional to the product of the current intensity and the voltage potential; in the case of alternating current, it is also
proportional to the cosine of the angle of displacement of the phases between the current and the voltage potential. Ferrodynamic and, less frequently, induction, thermoelectrical, and electrostatic wattmeters are also used.
4. The power to a 25-watt tungsten lamp is being measured with a voltmeter and an ammeter. The voltmeter, the resistance of which is 15,000 ohms, is connected directly across the lamp terminals. When the ammeter reads 0.217 amp, the voltmeter reads 120volts; determine: (a) true power to lamp; (b) percentage error introduced if voltmeter power is neglected. a.)
*Current through the voltmeter: I=V/R I=120/15kΩ I=8mA
*By KCL: Iin=∑Iout 0.217A=0.008A + I lamp Ilamp=0.209A
Plamp=VlampIlamp Plamp=(120V)(0.209A)
Plamp = 25.08W
b.) Percentage Error=((|Measured Power-True Power|)/True Power)100 % Error= (|25-25.08|/25.08)100
% Error = 0.3190%
5. The resistance of the ammeter of Problem 3 is 0.05 ohm. The voltmeter is now connected directly across the line. With the line voltage remains unchanged, determine: (a) voltmeter reading; (b) true power now taken by the lamp; and (c) power given by the product of the voltmeter and ammeter readings; (d) percentage error is the product in (c) is used. a.) Vsource=Vvoltmeter 6. Determine the power absorbed by a resistor that takes a charge of 3.5 coulombs flows in 2 seconds from a 220 – V source?
I=∆Q/∆t I=3.5C/2s I=1.75A P= VI P= (220V)(1.75A) P= 385W
REFERENCES
http://en.wikipedia.org/wiki/Power_(physics)
http://sun4.vaniercollege.qc.ca/cgi-bin/em/ofmt?section=1&subsection=8
http://www.lightandmatter.com/html_books/lm/ch21/ch21.html
