Physics 2225: Working With Electronic Equipment Purpose Learn how to use basic electronic equipment: Digital multi meter Oscilloscope Function generator

Physics 2225: Working With Electronic Equipment

PurposeLearn how to use basic electronic

equipment:• Digital multi meter • Oscilloscope • Function generator• Bread board

Apply and verify Ohm’s laws.


Digital Multi Meter (“DMM”)

A DMM is a device to measure• voltage,• current,• resistance,• and more….depending on the model

There are two modes to measure voltage and current:•“AC” (alternating current)•“DC” (direct current)

You need to know whether you are measuring an “AC” or “DC” current/voltage and set your DMM accordingly. Otherwise your measurement is wrong.

Note: We use the term “DC” or “AC” also for voltages, even thoughThe “C” stands for “Current” (Example: 5V DC).


Measuring AC with a DMMV or I

time

AC

If you measure this AC voltage/current in the “DC” mode, the result is the average (averaged over time) value (in this case zero).

average value

If you measure this AC voltage/current in the “AC” mode, the result is the the peak value divided by (assuming a sinusoidal oscillation around zero).2

AA

A707.0

2

Always measure AC in the AC mode.


Measuring DC with a DMM

V or I

time

DC

If you measure this voltage/current in the “DC” mode, the result is the average (averaged over time) value, which equals the DC value.

average value

Always measure DC in the DC mode.


Setting AC or DC on DMM (Fluke 87)

DC voltage

AC voltage

Current:Switch betweenDC and AC bypushing theblue button.


Setting AC or DC on DMM (MultiTec 320)

Voltage:Put dial to “V”.Switch betweenDC and AC bypushing theDC/AC button.

Current:Put dial to mA or A.Switch betweenDC and AC bypushing theDC/AC button.


Measuring a Voltage with the DMMVoltmeters have very high resistance. Very little current will flow through a voltmeter even if V is high. It is hard to damage a voltmeter.

Voltmeters are connected “in parallel” to measure the voltagebetween two points.

0.003

COM V

V

Resistor

5 V

GND = 0 V

current

A very tiny amount of current (ideally almost zero) goes through the voltmeter.

Important: Use COM (ground) and V ports for voltage measurement!


Measuring a Current with the DMM

Current meters (“amp meters”) have very low resistance. When hooked up to an even small voltage difference, a large current would flow through a current meter. It would be easy to damage a current meter. Current meters are protected by a fuse (if you blow the fuse the current meter will no longer work until the fuse is replaced).

Amp meters are connected “in series” to measure the current in a circuit.

0.003

COM V

A Resistor

5 V

GND = 0 V

current

Important: Use COM (ground) and mA or A (large currents) ports for current measurement!

mA


NEVER DO THIS !!!!!!!!!!!!!!!!!!!!!!!!!!!

0.003

COM V

A Resistor

5 V

GND = 0 V

huge current

Because the amp meter has almost no resistance, it gives the electrons an easy path between 5V and ground. Huge current through amp meter will blow the fuse.

A

Fuse will blow out !!!


The Correct Way, Again

0.003

COM V

A Resistor

5 V

GND = 0 V

current

NoticeIf you follow the path of the current you can see that it is forced to go through the resistor,which limits its current (by Ohm’s law….Current = Voltage / Resistance).

mA


The Function Generator

• Time-varying voltage/current.• Three different wave shapes (sinusoidal, square, triangular).• Variable frequency.• Variable amplitude of the signal.• DC offset of signal.


The Function Generator – Wave Shape Selection

Sinusoidal Wave

Square Wave

Triangular (“Sawtooth”)Wave


The Function Generator – Frequency Range

Up to 5 Hz

Up to 50 Hz

Up to 500 Hz

Within each range you can vary the frequency (see next slide).


The Function Generator – Frequency Variation

Coarse regulation

Fine regulation

Display of frequency:For low frequenciesyou need to wait a few seconds for the correctvalue to show (it takestime to measure it).


The Function Generator – Output Level

Signal output: Connect BNC cable here.

Adjust the amplitudeof the signal at “Output Level”.


What is “DC Offset” ?

0 VoltNo “DC offset”

0 Volt

2 Volt

Signal has “DC offset”of + 2 Volts (the signal fluctuates around +2 V instead of 0 V).


The Function Generator – Generating a “DC Offset”

Push “DC OFFSET”Button IN to enableDC offset adjustments.

Adjust the amount ofDC offset here.


The Heathkit “Bread Board”

Called “Bread Board” because you can use itto “breed” electriccircuits.

The board allows you to test your circuitsbefore you build apermanent version.


The Heathkit “Bread Board” – the Actual “Board”

This is the board:

Makes connecting electric components(resistors, capacitors,integrated circuits…)EASY.


How the “Holes” are Connected

5 holes in a“column” areelectricallyconnected.

But:Red and Greenare NOT connectedacross the center break.

The center break


How the “Holes” are NOT Connected

Holes in a“row” areelectricallyNOT connected.


How the “Holes” are NOT Connected

Top break

Holes are NOT connectedacross the top break.

Note: Many of our bread boards do not have the double row above the top break any more.


Power Supply to the Bread Board

Main Power: Switches all voltagesON or OFF.

GND = 0 Volts (“Ground”)

Example:To get 5 Volts:Use GND and +5


Example of Setting up a Simple Circuit

Resistor

5 V

GND

5VR Circuit Diagram

A more pictorial view of thesame circuit.


And How it Looks on the Bread Board


And from Another Angle…..

Notice, how wetake advantageof the hidden connections between theholes in acolumn.


Binary Numbers

In digital electronics information is coded as binary numbers whichcontain only Ones and Zeroes.

Example: 1001 (binary) = 1x23+0x22+0x21+1x20 = 9 (decimal)

Any decimal number can be converted to a binary number and storedelectronically (e.g., in a computer).

1’s and 0’s are often stored as High (5Volt) and Low (0 Volt) voltages.

For example, the number shown above (1001) could be represented by 4 “data lines” that have either high or low voltages.

5V 5V0V 0V

1 0 0 1


Data Switches, Logic Indicators

The bread board has “Data Switches” providing “High” and “Low” voltage for digital logic .

The bread board also has LEDs (Light Emitting Diodes) which act as logic indicators (a quick way to find out whether a voltage is “High” or “Low”).

Switch

Output(low or high)

5V (SW2 up)

0V (SW4 down)


Resistor Color Code

Our resistors have 4 colored bands on them. See your manual for color code.

Gold = 5% uncertainty

First bandRed = 2

Second bandBlack = 0

Third bandBrown = Multiplier 10 W

Resistance = 2 0 * 10 W = 200 W 10 W


The OscilloscopeA device to display a voltage as a function of time (useful for voltages that vary with time – e.g. oscillating signals). You can display 2 signals simultaneouslyusing the two input channels (Ch.1 and 2).

time

Voltage

Channel 1 input Channel 2 input


Changing the Horizontal (Time) Scale

Change horizontaltime scale here.


Changing the Vertical Scale on Channel 1

Change the verticalscale here.

For more optionson how to usechannel 1 pressthe MENU button.

The little knob shifts the signalup or down (unlessthe cursor is used).


Using the Cursor

Press the CURSORbutton to enable thecursors.

Once the cursorbutton is pushedthese two knobsmove the twocursors.


Using the Cursor

Change the type ofcursor betweenvoltage cursor ortime cursor with thisbutton.

Indicates voltage atwhich cursors 1 and2 are.

Indicates voltagedifference betweencursor 1 and 2.


Time Cursor Selected

The two timecursors.


Connectors and Their Names

“BNC” cable

“Shield”

Center pin

A BNC cable is basically a double cable:One “cable” is the center conductor ending in the center pin.The other “cable” is the “shield”. A BNC cable can do the job of two parallel wires.


An Adaptor Used in this Lab

Adapter: BNC (female)to Banana (male)

“Ground” indicator:Indicates that this sideof the banana end connectsto the “Shield” of the BNCconnector.The other banana end connectsto the center conductor of theBNC.


Suggestion for Using Cables and DMM

BNC small clips easilyattach to resistors etc.

Use adapter to plug into DMM

The “Ground” plugon the BNC/Bananaadapter connects tothe small black clip.


More…..

• More and different types of cables can be throughout room 405 hanging on the walls.

• There are also more and other types of adapters in the brown cabinet labeled “L” to the left of the entrance or they may be on the shared table.

• Should – against all warnings – you blow a fuse on yourDMM, ask your TA for a replacement.


Checking Fuse on Mutitec320 DMM is Easy

Just dial to “mA” and the display should look like this.

This symbol indicates a broken fuse.

Other types of DMMshave no indicator.

Documents

Physics 2225: Working With Electronic Equipment Purpose Learn how to use basic electronic equipment: Digital multi meter Oscilloscope Function generator