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SAN FRANCISCO STATE UNIVERSITY ELECTRICAL ENGINEERING

Experiment #2 Digital Multimeter and Power Supply

Objective To become familiarized with the use of the Agilent E3630A Triple Output Power Supply (PS) and the Agilent 34401A Multimeter (DMM).

Introduction A Triple Output Power Supply is a DC voltage source. It can provide a constant 0 to +6 volts, a constant 0 to +20 volts, or a 0 to ± 20 volts. The Digital Multimeter (DMM) on your work station can be used to measure five electric circuit variables: resistance, dc voltage, dc current, ac voltage, and ac current. (It can also measure temperature but we will not use this function in the course.) Make sure to select the appropriate variable to be measured with the DMM first before connecting the test leads to the circuit.


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TRIPLE OUTLET POWER SUPPLY

USING THE 0 to +6 VOLT ADJUSTABLE SINGLE SUPPLY

+6VLINE

AGILENT E3630A TRIPLE OUTPUT POWER SUPPLY

+20V -20V

OUTPUT METER

VOLTAGE

On/Off

COM +20V +6V -20V

+6V ±20V Tracking

ratio

Push this button to view display for 0 to 6 volts Plug probes into +6V and COM

(the circuit ground) for 0 to 6 volts

Adjust voltage level here

Display screen

o Plug probes into the +6V terminal and the COM terminal (the circuit ground) of the OUTPUT.

o Push the +6V button to enable the 0 to 6 volt power supply. o Adjust the +6V knob for the desired voltage output between 0 and 6 volts. o View voltage output on display screen.


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USING THE 0 to +20 VOLT ADJUSTABLE SINGLE SUPPLY

+6V LINE


+20V -20V

OUTPUT METER

VOLTAGE

On/Off

COM +20V +6V -20V

+6V ±20V Tracking

ratio

Push this button to view display for 0 to +20 volts Plug probes into COM (the circuit

ground) and +20V for 0 to +20 volts

Display screen


o Plug probes into the COM terminal and the +20V terminal of the OUTPUT.

o Push the +20V button to enable the 0 to +20 volt power supply. o Adjust the +20V knob for the desired voltage output between 0 and +20

volts. o View voltage measurement on display screen.


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USING DUAL 0 to ±20 VOLT POWER SUPPLY with FIXED TRACKING RATIO

+6V LINE


+20V -20V

OUTPUT METER

VOLTAGE

On/Off

COM +20V +6V -20V

+6V ±20V Tracking

ratio

Push this button to view display 0 to +20 volts


Set Tracking ratio to FIXED Display screen

Push this button to view display 0 to -20 volts

Plug probes into here for +20 volts and –20 volts and

Com (the circuit ground)

o The purpose of having a fixed tracking ratio is to maintain a minus voltage

that is the same as the plus voltage with respect to the Common (COM). o Make sure the Tracking ratio knob on the Power Supply is set to Fixed,

to ensure that the ± voltage supplies track each other as the voltage is varied.

o Plug three probes into the +20V terminal, the –20V terminal and the

COM terminal of the OUTPUT. o Vary the voltage using the ±20V knob. o View the positive supply by pressing the +20V button, then view the

negative voltage supply by pressing the –20V button; they will be at the same voltage but opposite polarities.


9

USING DUAL 0 to ±20 VOLT POWER SUPPLY with TRACKING RATIO

+6V LINE


+20V -20V

OUTPUT METER

VOLTAGE

On/Off

COM +20V +6V -20V

+6V ±20V Tracking

ratio

Push this button to view display 0 to +20 volts

Adjust positive voltage level here first Display screen

Plug leads into here for +20 volts and –20 volts and Com (the circuit ground)

Tracking ratio knob: Use to set negative supply value

Push this button to view display 0 to -20 volts

o The Tracking ratio knob enables the plus / minus voltage supplies to track each other in a constant ratio as the positive voltage is varied; this is useful when the negative supply is different from the positive supply.

o For example, if the positive voltage supply is set to +20 Volts using the

±20V knob and the negative voltage supply is set to –10 Volts using the Tracking ratio knob, then we have established a ratio of 2:1, with the positive voltage equal to twice the negative voltage.

o Without altering the Tracking ratio knob, adjust the positive voltage

supply from +20 Volts to +10 Volts using the ±20V knob, and observe (by pressing the –20V button) that the negative power supply is now –5 Volts, thus maintaining a ratio of 2:1 with positive voltage supply still twice the negative voltage supply.

Experiment #2

Digital Multimeter and Power Supply

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MULTIMETER

MEASURING RESISTANCE

4

resistor1k

Black probe

Red probeDisplay screen

Auto / Manual button

Push Ω 2W button to measure resistance

AGILENT 34401A MULTIMETER

1000 VOLTS MAX

3 AMPS RMS

V Ω

Terminals

I

L

HI

Min Max

Null Cont))Freq Ω 2W AC V DC V

Shift ٧ ^< >

5 6Auto/ Man

Auto/ HoldSingle

On/Off Recall

dBm dB Period Ω 4W AC I DC I

Power

o Plug the red probe into the red terminal VΩ labeled HI and the black probe into the black terminal labeled LO.

o Make sure Terminals button is set to the “Out” position for front

connecting terminals. o Press Ω 2W button to measure resistance. o Press Auto / Man button so that the “Man” disappears from the display;

the automatic mode is now in effect. o Place probes across resistor, then view the resistance value on the display

screen.


11

MEASURING VOLTAGE

4

+

_AC or DCVoltage

Black probe

Red probe

Display screen

Auto / Manual button

Push AC V to measure AC voltage

Push DC V to measure DC voltage

AGILENT 34401A

1000 VOLTS

3 AMPSRMS

V Ω

Terminal

I

L

HI

Min Max

Null Cont))Freq Ω 2W AC V DC V

Shift ٧ ^< >

Auto/ HoldSingle

6Auto/ Man

5On/Off Recall

dBm dB Period Ω 4W AC I DC I

Powe

vS

o Plug the red probe into the red terminal VΩ labeled HI and the black probe into the black terminal labeled LO.


connecting terminals. o Press DC V button to measure DC voltage (or press AC V button to

measure AC voltage). o Press Auto / Man button so that the “Man” disappears from the display;

the automatic mode is now in effect. o Measure the power source with the probes, then view the voltage

measurement on the display screen.


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MEASURING CURRENT

4

Powe

DC I AC I Ω 4W Period dB dBm

On/Off Recall 5 6Auto/ Hold

< > ^٧Auto/ Man

Single Shift

DC V AC V Ω 2W Freq Cont)) Null Min Max

HI

L

ITerminal

V Ω

3 AMPS RMS

1000 VOLTS

AGILENT 34401A

Press Shift and DC V to measure DC current Auto / Manual button

Shift button enables current measurement

Press Shift and AC V to measure AC current

↓ i

R1

1kV1

5Vdc

0

Red probe

Black probe

Display screen

CAUTION: For current measurements, the probes must be in series with the load only and current limited to less than 3 amps. If the circuit draws 3 amps or more, a fuse will blow and disable the instrument.


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MEASURING CURRENT (cont.) o Insert the black probe into the black terminal labeled LO; then insert the

red probe into the red terminal labeled I (at the bottom of the right-hand corner) for current measurements.


connecting terminals. o Press the Shift button and the DC V button to measure DC current. o Press the Shift button and the AC V button to measure AC current. o Press Auto / Man button so that the “Man” disappears from the display;

the automatic mode is now in effect. o Measure the current with probes in series with the load; then view the

current measurement on the display screen.


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Laboratory Work A. Resistance Measurements

1. Set up the DMM to measure resistance. Without connecting the test leads to anything, what does the display read? Why? Connect the two test lead together, what is the reading now? Why?

2. The color codes of four resistors are given below.

a. brown, black, yellow, xxx b. green, brown, orange, xxx c. yellow, violet, red, xxx d. blue, gray, brown, xxx

where xxx represents either gold, silver, or no band. Pick out these four resistors from your bag of components, record the fourth band of the actual resistors used, and determine their nominal values and tolerance (see Appendix D). Order these resistors according to increasing value of resistance, R1 for the smallest and R4 for the largest.

3. Measure each of the four resistors. Are the resistor values within

tolerance? (see p. 4 on how to determine accuracy)

4. Verify that two resistors connected in series exhibit an overall resistance equal to the sum of the two individual resistances. Do this for the pairs R1-R2, R2-R3, R3-R4, and R1-R4. Comment on the result in each case.

5. Verify that two resistors connected in parallel exhibit an

overall resistance equal to the product over the sum of the two resistances. Do this for the pairs R1-R2, R2-R3, R3-R4, and R1-R4. Comment on the result in each case.


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B. DC Voltage Measurements

1. Set up the DMM to measure dc voltage. Without connecting the test leads to anything, what is displayed on the DMM? Why? Connect the two test leads together, what is the reading? Why?

2. Connect R1, R2, R3, and R4 in series as shown.

+5V

R4

PowerSupply

R1

COM

R2 R3

Red Probe

Black Probe

Voltmeter

Resistors in Series

3. Measure the voltage drop across R1 with the red probe on the +5V side and the black probe between R1 and R2. What is the voltage reading? Now exchange the red and black probe. What is the voltage reading? Comment. The conventional approach is to use the black probe so that it is “closest” to the COM (which is the “ground” reference of the circuit), and to use the red probe so that it is “closest” to the Voltage source (+5 volts in this circuit).

4. Measure the voltage drop across the remaining resistors R2, R3, and R4. What is

the sum of the voltage drops? Comment. 5. Knowing the voltage drop across each resistor, use Ohm’s Law to calculate the

current through each resistor. Comment. 6. Using the sum of the voltage drops across the resistors and the sum of the

resistors, use Ohm’s Law to calculate the current. Comment.


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C. DC Current Measurements

1. Set up the DMM to measure dc current. Without connecting the test leads to anything, what is displayed on the DMM? Why? Connect the two test leads together, what is the reading? Why?

2. Set up the parallel circuit. Adjust the output of the power supply to 5 V. Place

R1, R2, R3, and R4 in parallel as shown and open connections across A, B, C, and D. Connect across point E.

3. Place an ammeter across A to measure the current through R1. What is the

current reading? Exchange the probes across point A. What is the current reading? Comment.

+5V

R4D

PowerSupply

E

R1

C

COM

R2

R3

B

A

Black Probe Red Probe

AMMETER

Resistors in Parallel


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4. Measure the current through the remaining resistors R2, R3, and R4. What is the sum of the currents through R1 to R4? Comment.

5. Knowing the current through each resistor, use Ohm’s Law to calculate the

voltage drop across each resistor. Comment. 6. Complete the connection across points A, B, C, and D and disconnect the

connection at point E. Measure the current through point E. How does it compare with the sum of the currents through the resistors?


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