General Lab Equipment Obstacle Course

A general primer in important equipment in a scientific laboratory.

Multimeters

This module will teach you about how to use the Fluke 179 True RMS multimeter. For this, you will need:

• Rigola DP1308A DC Power Supply
• Rigola DG1022 Function Generator
• An assortment of short wires
• 3 Resistors: 500ohm, 1kohm, 2kohm
• 3 Capacitors:
• A diode: one 1N4148
• A breadboard (or protoboard)

You'll learn more about the Power Supply and Function Generator later, but we'll need a minimum of functionality from them to make measurements with the multimeter.

• Measuring voltage
  Connect two probes to the right most inputs to the multimeter. I would recommend using probes with pointed tips or alligator clips at the end. The bottom input is the common/ground input and the upper right input is the voltage/resistance/diode. input. For simplicity, I'll refer to the probe connected to the voltage/resistance/diode input as the "red" probe and the probe connected to the ground input as the "black" probe. Turn the dial on the multimeter so that it points to V (with a line/dashed line over it) . This mode measures constant (DC) voltages, or will measure the RMS voltage of an alternating current. It measures the voltage difference between the top input and the common input (Vmeas = Vtop - Vbottom).
  1. To verify this, touch your two probes together. What does the meter read? Does this make sense? What is the voltage difference between two points without any resistance between them?

  Now, turn on the power supply. Hopefully, the yellow box on the screen will be highlighted. If not, press the +25V button on the power supply (above the yellow line) to change to that output. Press the left most button under the screen, so that VOLT is highlighted. This will give you control over the voltage output of the power supply. You can verify this by seeing that one of the numbers in the voltage box has turned white.

  Connect the positive output of the power supply (yellow) to one row of inputs on the breadboard and the common output of the power supply (labelled as "COM") to another row. Between these two rows, plug in the 1kohm resistor.

  Turn on the yellow output by pressing the center ON/OFF button (under the yellow box). The black OFF box at the top of the yellow window should change to a green ON box. Use the right/left arrows on the directional control buttons to highlight the tenths digit of the voltage line. Use the up/down buttons to change the voltage output to 00.50V. The box should be out putting half a voltage now.

  

  Voltage Measurement
  2. To verify this, touch the red probe to one end of the 1kohm resistor and the black probe to the other end. What does the multimeter read (as shown to the right)? If it reads 0.00, make sure the connections to the power supply are secure.
  3. If you flip the locations of the probe, what do you think will happen? Take a guess, then try it.

  Replace the 2kohm resistor with the 500ohm resistor and 2kohm resistor in series (that is, end-to-end so current flows through one and then the other).

  4. Using your knowledge of resistors in series, what do you think the voltage dropped across the 500ohm resistor will be? What about the 2kohm resistor?
  5. Measure the voltage across each resistor separately (place the probes on either side of one resistor, then on either side of the other). Were your guesses correct?

  Change the dial on the multimeter to the mV symbol with the line and dashed line over it. This is the millivolte measuring mode. It measures voltages the same as the voltage mode, but it reports results in millivolts and gives more accurate measurements for small voltages.

  6. Measure the voltages across the resistor pairs again. Do you get what you'd expect in mV?
• Measuring current (check that fuse isn't blown!)

To measure current, you need to use either of the left inputs and the common input to the multimeter. Both of the left inputs measure currents that flow INto these inputs and then OUT of the common input (black probe). This means the multimeter must be in-line with the current to measure it. The top-left input measures currents up to 400mA and the bottom one can measure currents up to 10A. The dial on the multimeter must be turned to the A (with line and dashed line) setting or the mA (with line and dashed line) setting. Like voltage, one will measure in A and the other in milliamps.

Change the multimeter to the milliamp setting. You'll note that on the right side of the screen, it will say "AC" under the unit listing ("mA"). Then, the meter will tell you the RMS current of an AC signal. This isn't what we want. Press the yellow 2nd button. The multimeter will beep and change to "DC" mode. This will report the DC current that flows through the multimeter.


Current Measurement
1. Based on what you know about electronics, how much current should traveling through the resistors?
2. As mentioned above, current measurements are done in-line. To do this, break the connection between the two resistors. Touch one multimeter probe to the free end of one resistor and the other probe to the free end of the other resistor (as shown to the right). Does the reading agree with your prediction?
3. Switch the probes. How does the current measurement change? Does this make sense?

Now, put the 1kohm and 2okhm resistors in parallel between the power supply lines.

4. Measure the total current drawn from the power supply. To do this, attach one multimeter probe to the the output of the power supply and the other probe to the ends of both resistors.
5. Now measure the current through just one of the resistors in parallel. To do this, unattach one resistor from the probe and attach the free end directly to the power supply line.
6. Using what you know about current, predict the current in the other resistor. Then measure it. does your measurement match your prediction?




• Measuring resistance and testing for continuity

The multimeter can be used for measuring resistance and for testing line continuity, that is checking that two points in a circuit are connected electrically.

Resistance measurements are straight forward. Attach the black probe to the common input (lower right) and the red probe to the voltage/resistance/diode input (upper right). Turn the dial to the resistance setting (capital greek letter Omega, Ω). Touch the probe ends to two points and the meter will read the resistance between the two probes.

1. Without the probes touching, what does the meter read? 0L stands for No Load - there is no electrical contact between the two probes. Technically, the multimeter can measure resistances up to 50Mohm, so 0L really indicates the resistance is greater than this value.
2. What do you think the multimeter will read if you touch the two probes together? Try it. Does your answer agree with the probe? A non-zero resistance is okay, as long as it is very close to one. The probe can report resistances down to 0.1 ohm, so hopefully your result is close to that.
3. Touch the probes to both sides of each resistor. Do the resistances that multimeter gives you agree with what the resistors say their resistances are? If not, does the multimeter measurement agree to within the tolerances listed by the resistors?
4. Combine some resistors in parallel and series. Calculate what you believe the total resistance should be with a given combination. Does the multimeter agree with your calculation?

The continuity test is similar to the resistance test. The multimeter will beep if there is electrical contact between the probes and the meter will report the resistance between the probes. Turn the dial to the symbol that looks like 4 right parentheses to use that mode.

5. Touch the probes together. What did the meter do?
6. Touch the probes to either side of the 1kohm resistors. What did the meter do?
7. Touch the probes to either side of the 10ohm resistor. What did the meter do?

The continuity mode is nice as you do not need to read anything, you can just listen for the beep. This is a good way to tell if components are connected correctly while soldering. However, as you hopefully observed, even if there is some resistance between the points the meter can beep - the multimeter's manual says that you will get a beep for resistances below 25ohm. This is sometimes problematic and you should instead measure the resistance. For example, if you think you have broken a resistor by running too much current through it, the resistor may still have some resistance and not trigger the multimeter's continuity test, but it's resistance has still fallen below what you need it to be for your application. Just relying on the continuity test to tell you if the resistor is good or bad is not sufficient.




• Diode check

The multimeter can be used to check diodes. Turning the dial to the continuity test mode (4 right parenthesis) then press the yellow 2nd button until a diode symbol appears on the screen. The red probe should be in the Voltage/Resistance/Diode input (top right). Touching the red probe to the annode side of the diode and the black probe to the cathode side of the diode should result in a beep from the multimeter, if the diode is functioning correctly.

1. Test that your diode functions correctly. Flip the probes, and check that the fluke does not beep.
2. If the multimeter has an extended beep, the diode is bad and there is a short in it. You can simulate this by touching the two probes together.
3. When testing the diode and it beeps, the multimeter will show a voltage on the screen. What do you think this voltage is?
   Unsure? Look through the diode's datasheet (available here).
   Still not sure? Squeeze the diode between your fingers and observe how the voltage reading changes. Squeezing the diode changes its temperature (just because it is absorbing heat from your fingers). Which property of the diode changes in the same way with temperature?




• AC signals, frequency response
• Capacitance
• Clamp meter

AC signals, frequency response

Capacitance

Clamp meter

Power Supplies

• Digital and Analog
• Floating and grounding
• Current/voltage limiting

Function Generators

(Should look at this in tandem with the following oscilloscope discussion)

• Frequency, amplitude, offset, phase
• Frequency sweep/ramp
• Sine, square (incl. TTL), triangle, sawtooth, arbitrary waveforms (possibly a demonstration of Fourier components)

Oscilloscopes

• Voltage/time scale
• Coupling
• Triggering
• Scope probes
• Termination
• Bandwidth, sampling
• Aliasing
• Analyzing data: cursors, averaging, math menu
• Exporting data
• Analog and digital scopes

RF Signals

• Measuring RF power
• Termination and impedance matching
• Attenuation and filtering
• Splitters, mixers, and switches

Lock-in Amplifier

• Basic idea of operation; reason for using
• Use switch to turn on and off a highly attenuated signal and detect it with the lock-in

Frequency Counters

Measure the frequency of an RF source; map frequency vs. voltage curve of a voltage controlled oscillator (VCO)

RF Spectrum Analyzer

Always be careful to ensure signal input to spectrum analyzer is not too large

• What does a spectrum analyzer do?
• Attach wire-loop antenna and find radio stations
• Mix two RF signals and observe the expected spectrum
• Measuring amplitude of signal above background
• Save and export data

Soldering

• Soldering technique
  • Cleaning iron tip
  • Heat pieces to be soldered (hot iron, short time)
  • Avoid cold solder joints
  • Look for shiny and smooth result
• Tools of the trade: heatshrink tubing, desoldering pump, solder wick, wire strippers, soldering gun, heat gun, rosin flux
• Solder end of DB9 cable (using only 4 or 5 conductors) to practice stripping wire, using heatshrink tubing, and creating usable product
• Construct voltage divider on perfboard with BNC input/output connectors