Assemble the circuit shown in Figure 1-1 using the 8102 Lodestar DC Power
Supply, a. 4.7kΩ fixed resistor and two “banana plug” leads. It is customary to use
a ...
EE-2302 Basic Measurements Purposes: (1) To familiarize the student with various virtual laboratory instruments and measurements of voltage, current and resistance and (2) to confirm that a simple circuit obeys the basic laws. Task 1. Our first goal is to measure a voltage (“Vs” in Figure 1-1) with several meters. Voltage is an indicator of the difference in energy level between two points in a circuit. Therefore the meter used for the measurement is connected to those 2 points (“-” and “+ “for “Vs”) in order to sense the energy difference.
8102 Lodestar
Task 1 – 1. Assemble the circuit shown in Figure 1-1 using the 8102 Lodestar DC Power Supply, a 4.7kΩ fixed resistor and two “banana plug” leads. It is customary to use a black lead for the common (COM) connection and a red lead for the “high” or “hot” side connection. While optional, we encourage you to do so in order to aid in “troubleshooting”. Turn the power supply knobs counterclockwise (CCW) and switch ON the supply. While observing the voltage meter (which is connected internally to “-” and “+”), turn up the voltage to about 8V. At this point we would expect about 8/4700 Amperes (1.7mA) of current from the supply (“+”) to the resistor (and back again through “-”). Unfortunately, this is such a small amount (compared to the scale of the current meter) that it is not readable. Record your best estimate of the voltmeter reading on the Data Sheet. Without changing anything else but while observing the voltmeter, disconnect (one end of) the resistor. [Note: In several places you are asked to connect or disconnect components while the circuit is “live”. Rest assured that the low voltage levels involved prevent these circuits from being hazardous to your health and you will not feel any “shocks” unless the equipment is faulty which is highly unlikely.] Presumably the current must change to zero when the resistor is disconnected. Record on the Data Sheet the amount of change, if any, that you observe in the voltage. Reconnect the resistor. [For the balance of Tasks 1 & 2, be careful not to change the power supply setting.] Task 1 – 2.
Next we will measure “Vs” using the Virtual Instruments Voltmeter. [Later we will see that this is a more accurate meter than the power supply meter.] Open the “VB DMM” icon and select the DC voltage button “V---“ as well as the 25 V range. Using banana plug leads, connect the voltmeter “-Vin” to the power supply “-” and the voltmeter “+Vin” to the power supply “+”. Again, black lead for “-Vin” and red lead for “+Vin” will help you avoid confusion. Your circuit should now look like the one in Figure 1-2.
NI 4060 8102 Lodestar
Record the voltage reading on the Data Sheet. Again remove the resistor while observing the Voltmeter and record the change, if any, in the NI4060 reading. Briefly change the voltmeter range to “2V” and observe the effect. Then change the range to “250V” and observe the effect. Reconnect the resistor. Task 2. Now we will see how to measure current (such as “I” in Figure 1-3) which requires a different connection than for voltage measurement. Recall that current is charge in motion. A current meter is like a turnstile through which the charge passes. To measure the current flow, it is essential that we break the circuit to insert the meter so that the charge must pass through it as shown in Figure 1-3.
8102 Lodestar
In this case we will use the multimeter as a current meter (ammeter). To do so, change the “V”olts setting to “A”mperes. Assuming that the ammeter has little or no resistance, we would still expect about 8/4700 A of current or about 1.7mA. Therefore, set the multimeter range to “2m” (milliamperes).
To connect the ammeter in the existing circuit properly: Remove the lead from the “+” to the resistor, connect the “+” to the multimeter “+mA” and the multimeter “-mA” to the resistor. [The convention is that positive current goes in the “+mA” terminal and out the “-mA” terminal.] Record the current reading on the Data Sheet. Disconnect the resistor and record the change in current. Reconnect the resistor, reverse the meter leads and observe the effect on the reading. Turn off the power supply and disassemble the circuit. Task 3. Ideally, if the voltage reading above in Task 1 are divided by the current reading in Task 2, the result (according to Ohm’s Law) should equal the resistance which was labeled 4.7kΩ. Perform those calculations (for the 3 voltage and 1 current readings) and enter the results on the Data Sheet. In most cases, the result is not exactly 4.7kΩ for several reasons: the meters are not perfect, the meters have varying degrees of readability as well as accuracy, and most likely the resistance is not actually 4.7kΩ. The 4.7kΩ label is a “nominal” value quoted by the manufacturer but the actual value varies due to manufacturing variations over a range of +/- 5 or 10% from nominal depending on the quality (and price) of the resistor. The 4th colored stripe indicates tolerance: gold = ±5%, silver = ±10%. To use the multimeter as an ohmmeter for resistance measurements, change the function setting to “Ω”. Set the range to “20k” and connect the resistor directly to the meter. [When making resistance measurements, the resistor(s) must be removed from any other circuitry and de-energized or the reading will be wrong.] Record the resistance on the Data Sheet and compare to the calculated values. Which calculated value is closest to the measured value? Is the measured value within the manufacturer’s stated tolerance? Reverse the leads and observe the effect on the reading. Task 4. The final task in this experiment is to determine whether a simple circuit obeys Kirchoff’s Voltage and Current Laws and gain measurement experience. Using the 8102 Lodestar power supply and fixed resistors, assemble the circuit shown below.
Task 4 – 1 Using the Multimeter, set the power supply voltage, Vs, to approximately 10V, measure and record all the voltages shown. Do these readings for each “window pane” add algebraically to zero and satisfy KVL? If not, you have done something wrong. Task 4 – 2 Use the multimeter to measure the currents shown above and record the readings on the Data Sheet. [Remember that the circuit must be revised to insert the ammeter properly for each measurement.] Do these readings add algebraically to zero and satisfy KCL? If not, you have done something wrong. Clean - up: When you have finished these measurements, turn off the equipment, put the equipment and leads in their proper “storage” locations and tidy up your station. Postlab Assignment: The data taken in this lab are to be handed in as recorded. If you want to make a photocopy of it for your own reference, you are welcome to do so. If you take it with you, the original must be in your instructor’s mailbox by 1 PM tomorrow and make sure your lab instructor initials your data sheet before you leave the lab!
EE2302 – Basic Measurements
Your Name: _________________________ Section: _________ DATA SHEET
TASK 1 VOLTAGE READINGS Task Meter Type Voltage Reading, V 1-1 1-2
Voltage change, V (resistor disconnected)
8102 Lodestar NI4060
TASK 2 CURRENT READING Task Current Reading, A
Current Change, A (resistor disconnected)
2
TASK 3 RESISTANCE Voltage, V (Task 1) Current, A (Task 2) Meter | Reading 8102 Lodestar | Same NI4060 |
RCALC, kΩ (V/I)
Which is closest to Measured resistance?
Measured Resistance: ___________ Manufacturer’s Range: __________ to__________ (kΩ) (kΩ) TASK 4 – 1
MEASURED VOLTAGES
Vs = ________, V1 = ________, V2 = ________, V3 = ________, V4 = ________ KVL: Vs – V1 – V2 = ________ (≈ 0?), TASK 4 – 2
V2 – V3 – V4 = ________ (≈0?)
MEASURED CURRENTS
I1 = _______, I2 = _______, I3 = _______
KCL: I1 – I2 – I3 = ________ (≈0?)
