be.01.11 potentiometers & rheostats instructor lab

8/4/2019 BE.01.11 Potentiometers & Rheostats Instructor Lab

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UNITED STATES MARINE CORPSMARINE CORPS COMMUNICATION-ELECTRONICS SCHOOL

TRAINING COMMANDBOX 788251

TWENTYNINE PALMS, CALIFORNIA 92278

INSTRUCTOR LAB HANDOUT

POTENTIOMETERS & RHEOSTATS

BE.01.11

BASIC ELECTRONICS COURSE

M092721

REVISED 12/12/2008

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TERMINAL LEARNING OBJECTIVES:

1. Provided cables, connectors, Test Measurement andDiagnostic Equipment, tools and a unit under test; testground electronics equipment, per the references. (2800-

ACT-1303)

2. Given a faulty electronic device, Test Measurement andDiagnostic Equipment and tools, diagnose basic electroniccircuits, per the references. (2800-ACT-1305)

ENABLING LEARNING OBJECTIVES:

1. Without the aid of references, given a schematic symbol ofa variable resistor, select the statement that identifies the

schematic symbol, per the references. (2800-ACT-1305c)

2. Without the aid of references, select the statement thatidentifies the characteristics of a variable resistor, per the

references. (2800-ACT-1303g)

3. Without the aid of references, given a rheostat schematic

and specified parameters, select the statement that

identifies the unknown circuit parameter, per the

references. (2800-ACT-1303ad)

4. Without the aid of references, given a potentiometer

schematic and specified parameters, select the statementthat identifies the unknown circuit parameter, per the

references. (2800-ACT-1303ae)

STUDENT INSTRUCTIONS:

1. Ensure that you have the primary references and StudentHandout SH BE.01

2. You will be responsible for the learning objectives.Ensure that you understand all the information contained inthe Student Handout. Studying your notes, reading thereferences, and completing the assigned homework willaccomplish this. The BE.01 Performance Examination and theBE.01 Written Examination will test the learning objectives.

3. Complete the practical application portion of this handout.

4. If you need extra help, ask!

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STUDENT HANDOUT PRESENTATION:

During this period of instructions you will be using the DCFUNDAMENTALS BOARD also known as board 1.

I. THE RHEOSTAT:

A. Ensure that the Base Unit Power Sourceis turned on. Ensure that the DC FUNDAMENTALS circuitboard is inserted into the base unit. Do not connectthe power supply to the circuit at this time.

B. Locate the LINEAR/NONLINEAR VARIABLERESISTOR CIRCUIT Block (refer to Figure 11-01).

Figure 11-01

C. Place switch S1 into the R2A position (up). Place atwo-post connector into the circuit as depicted inFigure 11-02. This will configure the variableresistor as a Rheostat by putting the resistiveelement in series with the load.

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Figure 11-02

D. Setup the multimeter to read resistance. Measure andrecord the resistance of R1 by placing the red leadinto the test point that is closest to the left of R1and the black lead into the test point that is closestto the right of R1.

1. R1 = _900 _____

E. Remove the multi-meter from the circuit. Turn thevariable knob of R2A to its lowest value (CCW).Insert the multi-meter into the circuit to measure thevalue of the variable resistor R2 by placing the redlead into the test point that is closest to the top ofthe resistor and the black lead into the test point

that is closest to the bottom of the resistor.Measure and record the value of the variable resistorwhile it is at 0%.

2. R2 at 0% = _0 _______

F. While the meter is still connected into the circuit,slowly turn R2A to its Full CW position (100%) whileobserving the changes in the resistive value of theresistor. Measure and record the value of R2 at itsFull CW position (100%).

3. R2 at 100% = _2.5k ____

G. Measure and record total circuit resistance with thevariable resistor in its Full CW position by placingthe red test lead into the test point that is closestto the left of R1 and the black test lead into the testpoint that is closest to the bottom of R3.

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4. RT at 100% = _3.41k ___

H. With the meter still in the circuit, slowly turn R2Afully CCW while observing the effect it has on RT.

Once the knob has been turned to its Full CCW positionmeasure and record RT at minimum resistance (0%).

5. RT at 0% = _900 _____

6. What effect does turning the knob on R2A to 0%have on total resistance?

Increases / Decreases

I. Setup the multi-meter to measure DC Current. Insert

the meter into the circuit by placing the red testlead into the test point that is closest to the top ofthe power supply and the black test lead into the testpoint that is closest to the left of R1. With the knobof R2A still in the Full CCW position (0%) measure andrecord the total current flow through the circuit.

7. IT at 0% = _16.48mA__

J. With the meter still inserted into the circuit slowlyturn the knob on R2A to its Full CW position (100%)while observing the effect it has on the circuitcurrent.

8. IT at 100% = _4.4mA____

K. Remove the Ammeter from the circuit and replace itwith a two-post connector. This will complete thecircuit and allow current to flow through thecomponents. Setup the multimeter to measure DCVoltage. With the knob of R2A still at its Full CWposition measure and record the voltage drop across R1by placing the red lead into the test point that is

closest to the left of R1 and the black test lead intothe test point closest to the right of R1.

9. VR1 at 100% = _3.7VDC___

L. With the meter still connected across R1 slowly turnthe variable adjustment R2A to its Full CCW position(0%) while observing the effect it has on the voltage

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drop of the resistor. Once it has been turned all theway measure and record the voltage drop across theresistor.

10. VR1 at 0% = _15VDC____

M. Remove the Voltmeter from across R1 and insert the redtest lead into the test point that is closest to thetop of (R2 which is to the right of R1) and place theblack test lead into the test point that is closest tothe bottom of the variable resistor (R2). With theknob still in the Full CCW position (0%) measure andrecord the voltage drop across the variable resistor.

11. VR2 at 0% = _0VDC_____

N. With the meter still connected in the circuit, slowlyrotate the variable resistor knob to its Full CWposition (100%) while observing the effect it has onthe voltage drop of the variable resistor. Once theknob has been turned all the way, measure and recordthe voltage across R2 at this time.

12. VR2 at 100% = _11VDC____

13. Did increasing the resistance of the variableresistor cause the voltage across R2 to increaseor decrease?

Increase / Decrease

O. Remove the two-post connector from the test pointsbetween the Power Supply and R1. Click on the rightarrow to advance to the next screen. Note that the CMlight has turned on indicating that CM-3 has beenactivated. Setup the multimeter to measure Ohms.Measure and record the resistive value of R1.

14. R1 = _900 _____

P. Move the Ohmmeter leads to measure the resistance ofthe variable resistor R2 by placing the red test leadinto the test point closest to the top of R2 and theblack test lead into the test point closest to thebottom of R2. With the variable knob R2A still in its

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Full CW position (100%) measure and record the valueof R2 at this time.

15. R2 at 100% = _1.23k ___

Q. With the meter still in place slowly rotate the shaftof R2A to its Full CCW (0%) position while observingthe changes in the resistive value of R2.

16. R2 at 0% = _0 _______

R. Measure total resistance in the circuit by placing thered test lead into the test point closest to the leftof R1 and the black test lead into the test pointclosest to the bottom or R2.

17. RT at 0% = _900 _____S. With the meter still connected to the circuit, slowly

rotate the shaft on R2A to its Full CW position (100%)while observing the effect it has on total resistance.

18. RT at 100% = _2.35k ___

19. Did turning the knob to 100% cause RT to increaseor decrease?

Increase / Decrease

T. Setup the multimeter to measure DC Current. Place themeter into the circuit at the two-post test pointsbetween the top of the power supply and R1. With theknob still at 100% measure and record the currentflowing through the circuit.

20. IT at 100% = _4.2mA_____

U. Slowly adjust the knob to its Full CCW position (0%)

while observing the effect it has on circuit current.Measure and record IT once you have reached the end ofthe resistors travel.21. IT at 0% = _16.48mA__

V. Remove the Ammeter from the circuit and replace itwith a two-post connector. Setup the multimeter tomeasure DC Voltage. Measure and record the voltage

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drop across R1 with the variable resistor still set toits Full CCW (0%) position.

22. VR1 at 0% = _15VDC____

W. Slowly rotate the shaft to the other extreme whileobserving the effect it has on the voltage drop of R1.Once the shaft is at its Full CW (100%) position,measure and record the voltage across the resistor.

23. VR1 at 100% = _3.8VDC___

X. Remove the meter from across R1 and connect it into thecircuit to measure the voltage across the variableresistor R2. With R2A still in its Full CW (100%)position measure and record the voltage across theresistor.

24. VR2 at 100% = _11VDC____

Y. Slowly rotate the shaft of R2A to its Full CCW (0%)position while observing the effect it has on thevoltage drop of R2. Once you reach the end, measureand record the voltage across the variable resistor.

25. VR2 at 0% = _0VDC_____

26. What effect does increasing the variable

resistance have on the voltage drop of R2?

Increases / Decreases

Z. Remove the test leads and all two-post connectors fromthe circuit.

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Click the right arrow to advance to the review questions.

Answer these questions on the screen as well as here in the lab

workbook.

1. A rheostat is identified by the fact that __________.

a. one of the end leads is connected in the circuit

b. the two end leads are connected in the circuit

c. one fixed and one variable lead are connected

into the circuit

d. all three leads are connected into the circuit

2. A rheostat is connected in __________ the load.

a. conjunction with

b. parallel with

c. series with

d. a different path than

3. Rheostats have __________ capabilities.

a. high current

b. high voltage

c. low current

d. low conductance

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4. Turning the shaft of a CW rheostat to its Full CWposition will cause __________.

a. RT to be at minimum

b.RT to be at maximum

c. IT to be at maximum

d. VL to be at maximum

5. When the shaft of a CW rheostat is turned to its FullCCW position the __________.

a. load resistance is RT

b. load resistance is half of RT

c. load voltage is at minimum

d. load current is at minimum

II. THE POTENTIOMETER:

A. Locate the LINEAR/NONLINEAR VARIABLE RESISTOR CIRCUITBlock. Place a two-post connector into the two-posttest points between the wiper arm and load resistor R3

(refer to Figure 11-03). Place switch S1 into the R2Aposition.

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Figure 11-03

B. Setup the multimeter to measure resistance. Measure

and record the value of R1 by placing the red test leadinto the test point that is closest to the left of theresistor and the black test lead into the test pointthat is closest to the right of the resistor.

1. R1 = _900 _____

C. Turn the variable knob R2A to its Full CCW setting

(0 ). Remove the test leads from the circuit.Reinsert the test leads to measure the resistance of R3by placing the red test lead into the test point that

is closest to the top of R3 and the black lead into thetest point that is closest to the bottom or R3.Measure and record the resistance of R3.

2. R3 at 0% = _0 _______

D. Leave the test leads in the circuit. Slowly turnvariable knob R2A to its Full CW position whileobserving the effect it has on the equivalentresistive value of the load resistor. Measure andrecord the value felt across R3 after reaching the Full

CW position.

3. R3 at 100% = _2.37k ___

4. Did the resistance increase or decrease as theknob was turned to its Full CW position?

Increase / Decrease

E. With R2A still at Full CW remove the red test lead

from the circuit and place it into the test point thatis closest to the left of R1 in order to measure totalresistance in the circuit.

5. RT at 100% = _3.28k ___

F. Slowly turn R2A to its Full CCW position whileobserving the effect it has on total resistance. Once

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the knob has been turned to its Full CCW position,measure and record the value of total resistance inthe circuit.

6. RT at 0% = _3.41k ___

G. Remove the test leads from the circuit. Setup themultimeter to measure DC Current. Insert the testleads into the two-post test points to complete thecircuit. Measure and record total current with R2Astill at 0%.

7. IT at 0% = _4.4mA____

H. Slowly turn the knob to its Full CW position whileobserving the effect it has on IT. Once you havereached the Full CW position (100%) measure and recordthe value of total current flowing in the circuit.

8. IT at 100% = _4.57mA___

9. Did IT increase or decrease as the knob was turnedtowards its Full CW position?

Increase / Decrease

I. Remove the test leads from the circuit and replacethem with a two-post connector to complete the

circuit. Setup the multi-meter to measure DC Voltage,and measure the voltage drop of R1 at Full CW.

10. VR1 at 100% = _4.16VDC__J. Slowly turn the variable knob to the Full CCW position

while observing the effect it has on the voltage dropof R1. Measure and record VR1 once you have reached 0%.

11. VR1 at 0% = _4VDC_____

K. Remove the test leads from their location and place

them in the circuit to measure the voltage drop of theload resistor R3. Measure and record VR3 at 0%.

12. VR3 at 0% = _0VDC_____

L. Slowly turn the shaft in the opposite direction whileobserving the effect it has on load voltage. Once you

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have reached the Full CW position measure and recordthe voltage on the load.

13. VR3 at 100% = _10.84VDC_

14. Did changing R2A to its Full CW position causethe voltage of the load in increase or decrease?

Increase / Decrease

M. Remove the two-post connector that is between VA andR1. Change switch S1 to position R2B (down). Setupthe multimeter to measure resistance. Measure andrecord the resistance of R1.

15. R1 = _900 _____

N. Remove the test leads from the circuit and reinsertthem across the load resistor in order to measure itsvalue at the Full CW value.

16. R3 at 100% = _2.37k ___

O. Slowly rotate the variable knob R2B to its Full CCWposition while observing the effect it has on loadresistance. Once you are at Full CCW measure andrecord the value of load resistance.

17. R3 at 0% = _0 _______

P. Remove the red test lead from the circuit and reinsertit so that total resistance can be measured. Measureand record RT with R2B at its Full CCW position.

18. RT at 0% = _3.4k ____

Q. Slowly rotate the shaft of R2B to its Full CW positionwhile observing the effect it has on RT. Once you havereached Full CW measure and record the value of totalresistance in the circuit.

19. RT at 100% = _3.28k ___

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R. Remove the test leads from the circuit. Setup themultimeter to measure DC Current. Insert the testleads into the two-post test points between the top ofthe power supply and the left side of R1. Measure andrecord total current with R2B set to its Full CW

position.

20. IT at 100% = _4.57mA___

S. Slowly rotate the shaft of R2b until you reach FullCCW while observing the effect it has on total currentin the circuit. Once you reach Full CCW measure andrecord the current flowing through the circuit.

21. IT at 0% = _4.4mA____

T. Remove the test leads from the circuit and replacethem with a two-post connector. Setup the multimeterto measure DC Voltage. Measure and record the Voltagedrop of VR1 at Full CCW.

22. VR1 at 0% = _4VDC_____

U. Slowly rotate shaft R2B until you reach the Full CWposition while observing the effect it has on thevoltage drop of resistor R1. Once the shaft has beenrotated to full CW, measure and record the value ofVR1.

23. VR1 at 100% = _4.16VDC__

V. Move the test leads so that you can measure loadvoltage. Measure and record this value with variableresistor R2B at Full CW.24. VR3 at 100% = _10.84VDC_

W. Slowly rotate the shaft to its Full CCW position whileobserving the effect it has on load voltage. Once youhave reached the Full CCW position measure and record

VR3.

25. VR3 at 0% = _0VDC_____

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X. Click on the right arrow to advance to the nextscreen. Note that the CM light has turned on whichindicates that CM-3 has been activated. Remove thetest leads from the circuit and setup the multimeterto measure resistance. Remove the two-post connector

from the two-post test points between the top of thepower supply and the left side of R1. Measure andrecord the resistance of R1.

26. R1 = _900 _____

Y. Remove the test leads from the circuit and repositionthem to measure the resistance of R3. Ensure that thevariable resistor switch S1 is placed in the R2Bposition. Measure and record the value of R3 with thevariable knob set at its Full CCW position.

27. R3 at 0% = _0 _______

Z. Slowly rotate the shaft while observing the effect ithas on the load resistance. Once you have reached theFull CW position measure and record the value of R3.

28. R3 at 100% = _1.19k ___

AA. Reposition the test leads so that total resistance canbe measured. With the switch still set at 100%

measure and record total resistance.

29. RT at 100% = _2.1k ____

BB. Slowly rotate the shaft of R2B until you have reachedthe Full CCW position while observing the effect ithas on total resistance. Once you are at the Full CCWposition measure and record the value of totalresistance in the circuit.

30. RT at 0% = _2.14k ___

31. What was the effect of moving the shaft of R2B toits Full CCW position on total resistance?

Increase / Decrease

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CC. Remove the test leads from the circuit and setup themultimeter to measure DC Current. Insert the testleads into the circuit to measure total current. Withvariable resistor R2B still set at 0% measure andrecord IT in the circuit.

32. IT at 0% = _7.03mA___

DD. Slowly rotate the shaft of R2B to its Full CW positionwhile observing the effect it has on total current.Once you have reached 100% measure and record thecurrent flowing through the circuit.

33. IT at 100% _7.13mA___

34. What effect did increasing the resistance of R2Bhave on the current flowing through the circuit?

Increase / Decrease

EE. Remove the test leads from the circuit and setup themultimeter to measure DC Voltage. Insert a two-postconnector into the circuit to energize it. Measureand record the voltage developed across R1 with theshaft still in the Full CW position.

35. VR1 at 100% = _6.49VDC__

FF. Slowly rotate the shaft until it reaches its Full CCWposition while observing the effect it has on thevoltage drop of R1. Once you have reached the Full CCWposition measure and record the value of VR1.

36. VR1 at 0% = _6.39VDC__37. What happened to VR1 when the variable resistor

was changed from Full CW to Full CCW.

Increase / Decrease

GG. Remove the multimeter leads and the two-post connectorfrom the two-post test points between the top of thepower supply and the left of R1. Setup the multimeterto measure resistance. Ensure that S1 is still in theR2B position. Insert the test leads into the circuitso that the resistance of R1 can be measured and recordthis value in the space provided.

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38. R1 = _900 _____

HH. Remove the test leads from the circuit and reinsertthem to measure the resistance of the load resistor.With the variable switch R2B still in the Full CCW

position measure and record the value of R3.

39. R3 at 0% = _0 _______

II. Slowly rotate the shaft of R2B until you reach theFull CW position while observing the effect it has onthe load resistance. Once you reach Full CW measureand record the value of R3.

40. R3 at 100% = _1.19k ___

JJ. Remove the red test lead from the circuit and place itinto the test point to the left of R1 so that totalcircuit resistance can be measured. With the shaft ofR2B still at 100%, measure and record total resistancein the circuit.

41. RT at 100% = _2.1k ____

KK. Slowly rotate the shaft of R2B to its Full CCW whileobserving the effect it has on total resistance. Onceyou are at Full CCW measure and record the value of RT.

42. RT at 0% = _2.14k ___

LL. Remove the test leads from the circuit and setup themultimeter to measure DC Current. Insert the testleads into the two-post test points between the top ofthe power supply and the left of R1 so that totalcurrent can be measured. With the shaft of R2B stillin the Full CCW position measure and record the valueof total current in the circuit.

43. IT at 0% = _7.03mA___

MM. Slowly rotate variable resistor R2B to its Full CWposition while observing the effect it has on circuitcurrent. Once you reach the Full CW position measureand record the value of IT in the space provided.

44. IT at 100% = _7.13mA___

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NN. Remove the test leads from the circuit and replacethem with a two-post connector so that the circuit canbe energized. Setup the multimeter to measure DCVoltage. Insert the test leads into the circuit to

measure the voltage across R1. With the shaft of R2Bstill at its Full CW position measure and record VR1.

45. VR1 at 100% = _6.49VDC__

OO. Slowly rotate the shaft of variable resistor R2B toits Full CCW position while observing the effect ithas on the voltage of R1. Once you reach Full CCWmeasure and record the voltage dropped across theresistor.

46. VR1 at 0% = _6.39VDC__

PP. Remove the test leads from the circuit and reinsertthem so that the voltage of the output is measured.With the shaft still at its Full CCW position measureand record the voltage of the load resistor.

47. VR3 at 0% = _0VDC_____

QQ. Slowly rotate the shaft of variable resistor R2B untilyou reach the Full CW position while observing theeffect it has on the load resistance. Once you reach

the Full CW position measure and record the voltagedeveloped across the load.

48. VR3 at 100% = _8.51VDC__

RR. Remove the test leads and all two-post connectors fromthe circuit.

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Click on the right arrow to advance to the review questions

screen. Answer all review questions on the computer as well as

in this Lab Workbook.

1. In an electrical circuit, a potentiometer primarilyprovides a variable __________.

a. voltage

b. current

c. resistance

d. power source

2. A linear taper potentiometer provides what percentageof total resistance at what percentage of shaftrotation?

a. 10% resistance at 50% rotation

b. 20% resistance at 25% rotation

c. 50% resistance at 50% rotation

d. 70% resistance at 75% rotation

3. A log taper potentiometer provides what percentage oftotal resistance at what percentage of shaft rotation?

a. 5% resistance at 25% rotation

b. 10% resistance at 50% rotation

c. 70% resistance at 75% rotation

d. 85% resistance at 100% rotation

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4. In this circuit, what is the maximum output voltageavailable at R2B?

a. 11VDC

b. 10.68VDC

c. 8.68VDC

d. 3.42VDC

5. With R2A set to its maximum CW position and R3 is notconnected to the circuit, a measurement of 8.7V wasfelt across R2A, this indicated that a CM caused__________.

a. R3 to have

a 4.7kresistorinparallel

b. R3 to have

a 2.4kresistorin series

c. R2A tohave a

4.7k

resistorin parallel

d. R2A to have a 2.4k resistor in parallel

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R1

910

R3

2.5k

(CW)

R2B

2.5k

VA

15VDC

R1

910O

R3

47kO

(MAX CW)

R2A

2.5kO

VA

15VDC

8.7 VDCMEASURED

(NO LOAD)


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CONCLUSIONS:

1. Rheostats usually have a limited range of values.

2. Rheostats have a high current-handling capability.

3. Rheostats are connected in series with the load device.

4. At maximum resistance on a rheostat, the voltage on theoutput is minimum, and the output current is minimum

5. Potentiometers have a wide range of values.

6. Potentiometers have limited current handling capabilities.

7. The load device is always placed in parallel with the short.

8. Potentiometers are always connected as a variable voltagedivider.

9. At maximum resistance on the potentiometer, outputresistance approaches maximum, output voltage is atmaximum, and output current is maximum.

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REFERENCES:

1. Operator Manual: Fluke 77/BN2. Basic Electronics (9th Edition), Grob

3. Introductory Electric Circuits, Robert T. Paynter

4. WinFACET, Lab-Volt Systems Inc.

REPARED BY: ____________________________________________TITLE: __________________________________________________SIGNATURE: ________________________ DATE: ______________MODIFIED BY: _P.A.DEDEAUX__________ DATE: _10/10/2007___APPROVED BY: ____________________________________________TITLE: __________________________________________________SIGNATURE: ________________________ DATE: ______________

be.01.11 potentiometers & rheostats instructor lab

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