Week 3: 25-31 January, 2016

  1.)  Compare the calculated and measured equivalent resistance values between the nodes A and B  for three circuit configurations given below.

Experiment 1 Schematics



The Table above shows the measured resistance values
from Point A to Point B for circuits a b and c. 

All measurements were within 1 Ohm of the values
calculated using the formulas above.  



  2.)  Apply 5V on a 120 Ω resistor. Measure the current by putting the Multimeter in series and parallel. Why are they different?

     
    If you put the Multimeter in series like you are supposed to, you will get the current reading that is going through the resistor. If you put the Multimeter in parallel, the current will just go through the Multimeter, skipping the resistor, essentially shorting the circuit.

  3.)  Apply 5 V to two resistors (47 Ω and 120 Ω) that are in series. Compare the measured and calculated values of voltage and current values on each resistor.

       

    By applying 5 Volts to both the a 47 and 120 Ohm resistor connected in series, we were able to collect the following voltage and current Data. 



Measured and Calculated Voltage and Current across
a 47 and 120 Ohm resistor connected in Series 

All Measured Voltages were within 1% of the calculated values

The Measured current was within 0.7 mA of the calculated value.



  4.)  Apply 5 V to two resistors (47 Ω and 120 Ω) that are in parallel. Compare the measured and calculated values of voltage and current values on each resistor.

Experiment 4 Schematic

The Voltage Measurement across the circuit above were as follows

Voltage across the 120 Ω resistor:  4.98 V 

Current through the 120 Ω resistor:  39.8 mA

Voltage across the 120 Ω resistor:  4.97 V 

Current through the 120 Ω resistor:  94.8 mA

These readings are consistant with the expected values since voltage is constant in a parallel circuit. The voltage measured at any point in the circuit should be equal to the 5 V applied by the power supply.

According to Ohm's Law Current = Voltage/Resistance, as such

5 V divided 120 Ohms = 41.7 mA  which is very close to the measured 39.8 mA 

and

5V divided by 47 Ohms = 106.4 mA  which is also close the measured 94.8 mA 

The variations between the calculated and measured values can most likely be attributed to a higher than expected resistances caused by using multiple sets of alligator clips and meter leads to construct and measure the circuit. 

  5.)  Compare the calculated and measured values of the following current and voltage for the circuit below:

a.       Current on 2 kΩ resistor, 

b.      Voltage across both 1.2 kΩ resistors. 

Photo of the circuit as laid out on our breadboard

Alternate view of the circuit as laid out on our breadboard



Experiment 5 Schematic with labelled Mesh Loops



Theoretical Voltages and Current Readings calculated using Mesh Analysis on the TI-Nspire CAS student software.

A.)  The current measured across the 2 kΩ resistor was 1.83 mA  Which closely matches the calculated I1 current of 2.05 mA.

B.) The Voltages were as follows 

(R1 refers to the 1.2 kΩ resistor drawn horizontally in the schematic above)

(R2 refers to the 1.2 kΩ resistor drawn vertically in the schematic above)

Measured Voltage Across R1:  1.149 V      

Measured Voltage Across R2:  1.045 V

Voltage across both 1.2 kΩ resistor was somewhat higher than the 0.88 V and 0.75 V calculated above.

  6.)  What would be the equivalent resistance value of the circuit above (between the power supply nodes)?

    The Equivalent Resistance for the circuit is equal to the applied voltage over the calculated resistance.  Since we are reading at the power supply we can use 5V as the Test voltage and 2.056 mA as calculated above for the I1 current. Using these values the equivalent resistance is calculated as 2.43 kΩ by dividing 5V by .002056A.

  7.)  Measure the equivalent resistance with and without the 5 V power supply. Are they different?  Why?

    Without Power resistance was measured at 2.73 kΩ which is close to the 2.43 kΩ calculated in question 6.

    With power applied the meter read "OL", this is because the current flowing through the circuit was overloading the Multimeter rendering it unable to take an accurate reading.

  8.)  Explain the operation of a potentiometer by measuring the resistance values between the terminals (there are 3 terminals, so there would be 3 combinations).

(video)

This video shows us using the potentiometer, and demonstrating how you can use it to put out a

constant 10KΩ, or using the first and second, or second and third pin to put out a variable resistance. 

     The resistance of the Potentiometer is measured as follow

    

    - T-1  to T-3 will always read the Potentiometer's maximum

       resistance (in this case 10 kΩ)

    - T-1 to T2 will vary from 0 to the Potentiometer's max value

       based on the knob's position
    - T-2 to T-3 will also range from 0 to the Potentiometer's max value
       again based on the knob's position.

-   * Note:  (T1 to T2) + (T2 to T3) = Potentiometer's Max value

-

  9.)  What would be the minimum and maximum voltage that can be obtained at V1 by changing the knob position of the 10 KΩ pot? Explain.

    If you have the potentiometer set to 0 Ω , there will be no voltage drop across it, because there would be no resistance. However, as long as the potentiometer is at anything other than zero, the voltage drop will always be 5 volts, with a varying amount current.

Experiment 9 Schematic

  10.)  How are V1 and V2 (voltages are defined with respect to ground) related and how do they change with the position of the knob of the pot?

(video)

Experiment 10 Schematic

A short Video showing how the potentiometer setting

affects voltage at V1 and V2

  11.)   For the circuit below, YOU SHOULD NOT turn down the potentiometer all the way down to reach 0 Ω. Why?



Experiment 11 Schematic

      If you turn the potentiometer all the way down to zero, turning it's resistance to zero, you would short the circuit, and all of the current would then go through the potentiometer since there is no resistance. We unfortunately did exactly this our first time doing this circuit, and fried the potentiometer.


    *  Question 11 was not added to this week's blog requirements until after we discovered the our potentiometer's inability to handle the circuit's maximum current.  

12.)   For the circuit above, how are current values of 1 KΩ resistor and 5 KΩ pot related and how do they change with the position of the knob of the pot?

(video).

Short Video showing the effects of the potentiometer setting on both the 1 kΩ resistor and 5 KΩ potentiometer's current readings. 

    As the video above demonstrates the potentiometer has no effect on the current running through the 1 kΩ resistor, this is because current is a function of Voltage and Resistance, and since voltage is constant throughout a parallel circuit and the resistor's value is fixed its current remains the same regardless of what value the potentiometer is set at.  The only exception to this rule would be if the potentiometer was set to 0 resistance in which case all current would bypass the 1 kΩ resistor and it would draw zero current.  This would be a bad idea however as this short circuit condition would damage the potentiometer as we discussed in question 11.  What the potentiometer setting does effect is the amount of current going through the potentiometer itself.  As resistance increases the amount of current decreases  and as resistance decreases the amount of current passing through the potentiometer will increase until a value of 0 Ω is reached at which point maximum current will pass through the potentiometer.



  13.)   Explain what a voltage divider is and how it works based on your experiments.

Voltage divider is the process of how voltage splits across different resistors in a series circuit as demonstrated above (See # 10).  For that circuit a 5 volt drop was observed across the two resistors. However, when the potentiometer was set to zero, the 1 kΩ resistor would drop the entire 5 volts, and when the potentiometer was to 10 kΩ, the 1 kΩ resistor about only about 0.45 volts  and the remaining 4.55 volts would drop across the potentiometer. 

You can think that the total voltage as being divided into 11 parts (since there was 11 kΩ of  total resistance), since 10 of the 11kΩ of resistance was provided by the potentiometer it receives 10 parts of the voltage,leaving only 1 part for the 1 kΩ resistor. 

  14.)   Explain what a current divider is and how it works based on your experiments.



    Current divider is the similar as voltage divider, but deals with current in a parallel circuit. This process can be seen in the circuit from #11. When two resistors are in parallel, the current wants to take the path of least resistance. In the circuit from #11, the current has two possible paths, the left loop through the potentiometer, or the right loop through the  1 kΩ resistor.  When the potentiometer was set to 10K, most of the current (about 90%)bypassed the potentiometer and travelled through the 1 kΩ resistor.  As the potentiometer's resistance decreased more current travelled through the potentiometer and less travelled through the 1 kΩ resistor 
    
    Similarly to Voltage Divider you can think that the current  as being divided into 11 parts (since there was 11 kΩ of  total resistance), however; when using the current divider rule as resistance increases current decreases so when the potentiometer is providing 10 parts of the total resistance it only receives 1 part of the total current, leaving 10 parts for the 1 kΩ resistor.

 
    Post contributors (C Ruby & K Pawlak)

Week 2, 18 - 23 January, 2016

  Due to the Holiday Monday we will only have one blog entry this week.
 
  Below are the questions posed to us by Dr. Kaya this week followed by our answers as well as pictures and videos for clarification purposes.

  1.)    What is the role of A/B switch? If you are on A, would B still give you a voltage?

The A/B switch is used to determine which potion of the power supply will be monitored by the built in Amp and Volt meters.  When” A” is selected the meters display the output amperage/voltage of power Supply A, and similarly if “B” is selected Supply B’s output will be displayed.   This switch only controls the integrated meters, and has no direct control over either supply, therefore it is possible for Supply B to be providing power while the A/B switch is in position A.

  2.)      In each channel, there is a current specification (either 0.5 A or 4 A). What does that mean?

The 5v fixed channel has a 4 Amp current capacity meaning it can supply a constant 5v at 0-4 Amperes of current.  The Variable Power Supplies on Channels AB can supply a greater range voltage (0-24v) but can only sustain a maximum current of 0.5 Amperes 

  

  3.)    Your power supply has two main operation modes for A and B channels; independent and tracking. 
         How do those operation work? (Video)

A Brief video with audio explaining the operation of our power supply's main operating modes.

  4.)    Can you generate +30 V using a combination of the power supply outputs? How? (Photo)

   Yes by putting the Power Supply in Series Tracking Mode and connecting the leads to Channel A's
         Positive output and Channel B's negative output the voltage can be increased to up to 48 volts.

Power supply configuration we used to achieve +30 V

  5.)     Can you generate -30 V using a combination of the power supply outputs? How? (Photo)
 
         Yes, -30 Volts can be achieved in the same manner as +30 Volts (See Question 4) with the only
         variation being reversing your connections so that the positive lead is plugged into the Negative
         output of Channel B, and the Negative lead in to the positive output of channel A.

Power supply configuration
we used to achieve + 30 V
(Also a pretty good photo bomb from Group 1)

  6.)    Can you generate +10 V and -10 V at the same time using a combination of the power supply     
         outputs? How? (Photo)

         To achieve +/- 10V simultaneously we used the Series Tracking Mode with both outputs using the
         Negative Channel A terminal for their grounds.  The +10V output was connected to the positive
         Channel A terminal, while the -10V output was connected to the Negative Channel B Terminal

Photo showing the power supply configuration
we used to achieve +/- 10V simultaneously

  7.)     Apply 5V to a 100 Ω resistor and measure the current by using the DMM (remember the setup in      DC 3). Compare the reading with the current meter reading on the power supply. At what angle of   
         the current knob makes the LED light on? If you keep on decreasing the current limit, what    
         happens to the voltage and current? (Video)


         The LED Light illuminated at approximately 20mA according to the integrated amp-meter. 
         The Current Knob was less than an eight of a turn above minimum at the time it illuminated.
         Both current and voltage decrease as the current limit is reduced.

Video showing the power supply connected to a 100 Ohm resistor as the current limit is decreased

  8.)   Where is the fuse for the power supply? What is it for?

        The Power Supply Fuse is located on the back side of the unit just below the power  cord.

        The Fuse protects the power supply's circuitry from over-current conditions

Power Supply Fuse

  9.)    Where is the fuse for the DMM? What is it for?

     

         The fuse for the DMM is located in the lower left corner of the front panel.  It protects the DMM  
         circuitry from an over current condition caused by connecting the meter to a circuit with an       
         amperage that exceeds the DMM's operating range.  A second fuse (not pictured) is located on the
         back of the unit this fuse protects the DMM from excess current coming from the wall outlet it is
         plugged in to. 

Front Panel of DMM.  Note the fuse holder in the lower left corner

 
  10.)   What is the difference between 2W and 4W resistor measurements?

   

           The two wire method of taking resistance is simpler but less accurate than the four wire method
          because it does not account for current loss due to resistance in the leads which can lead to
          inaccurate readings in circuits with small amounts of resistance.  The four wire method is a bit
          more complicated to set up but increases accuracy by using four leads (2 to measure amps two to
          measure volts) then calculating resistance based on measured current and voltage

  11.)   How would you measure current that is around 10 A using DMM?

          To measure a current of approximately 10 Amps you would plug your positive lead into the Red
          15A max Fused port on the DMM and the Negative lead into the Black port.  You then need to turn
          the range selection to manual using the "Auto <" button and manually select the appropriate range
          using the up and down arrow buttons.

Wednesday, January 13th

1. To measure the current with the DMM, you must break the circuit, and then complete the circuit through the DMM. To measure the voltage, you just have to put your leads from the DMM across the point at which you want to measure, such as the resistor in our case.

2. You can get 3 different voltages with the power supply. The first output is fixed at 5 volts, while the second two outputs are adjustable, from 0-24 volts.

3.


Here is a image of our first practice circuit on the right. On the left is a picture of the resister we burned while testing Ohm's law.



Here is a video of our setup for testing Ohm's law.



4.  Ohm's Law Data

Above is the data we collected from testing Ohm's law. We used a 100 ohm resister for the first test, and a 820 kilo-ohm resistor for the second test. We repeatedly ran different voltages over the two resistors, and measured the current that passed through them. We then used Ohm's law, RI=V, to see if the resistance values matched up. They were not exact, but they were close. For the 100 ohm resister, we found the the resistance was diminishing with each trial, but that was because we were slowly burning it. For the 820 kilo-ohm resistor, our results were a little more jumpy, but it could have been to human error. They were still in the ball park of 820. Below is a picture of our setup. The previous video showed the same setup.

5. Here is our video of our Rube Goldberg Machine Circuit. 

 

Chris Ruby

Friday, January 15th

Today we discussed some possible uses for the circuit we wired on Wednesday.
As a refresher the the circuit consisted of a DC Motor that wired to a photo sensor which would activate the motor when light was detected and increase the motor's speed as the light became more intense.

Rube Goldberg Circuit Diagram #1

Click on Image to Enlarge.

A few possible use for this circuit in a Rube Goldberg machine would be either to to wind up a line, similar to a fishing reel, when this line became tense it could cause any number of triggers such as pulling a lever, or opening a door to to activate the next next segment of the machine.

A second possibility would be to connect a paddle to the motor which could either set a ball in motion or knock over a row of dominoes, again ttrigger the next portion of the circuit.

KP

Monday, January 11th

So Monday was the First Day of class.

The course will be formatted as follows;

  Mondays                      Wednesdays                         Friday
  - Pre-Lab Quiz             - Lab                                    - Blog Discussion
  - Lab Intro                    - Wrap-Up                           - Post-Lab Quiz 
  - Lab 
  - Wrap-Up

The Final Course Grade will be based on a 1000 pt total comprised of the following
- 30 Quizzes            (10 points each / 300 points total)
- 15 Discussions      (10 points each / 150 points total)
- 15 Blog Reports    (20 points each / 300 points total)
- 2 Midterms            (50 points each / 100 points total)
- 1 Final Exam         (150 points each / 150 points total)

-- We were also given a written safety brief with the following highlights.

     1.) Do not work alone on energized components
     2.) Switch off all power when assembling an experiment or project
     3.) Keep one hand behind your back and use an insulated probe whenever measuring an energized 
          circuit.
     4.) Never work on electrical equipment when you have wet hands or are standing on a wet floor.
     5.) Never touch two pieces of equipment simultaneously
     6.) Never lunge for or attempt to cut falling parts of a live circuit

** Additional safety rules can be found in the Course Syllabus  (Link requires Blackboard Access)

-- Another Part of the Safety Briefing discussed the danger of electrical current.  Unlike Voltage a 
    very small amount of current can be lethal. 
    
     - A current as small as 0.01 Amps can be cause a painful shock, muscle paralysis and labored  
        breathing
     - A current of only 0.1 to 0.2 Amps is known as the lethal current and can stop your heart
     - Currents of 1 Amp or Greater are more violent and cause a severe burn and leads to death 
        by asphyxiation caused by muscular paralysis of the lungs and diaphragm.    

--Daily Experiment:  Reading Resistor Color Codes

Video Intro

Full Resistor Color Code Chart

Click on Image to Enlarge

--Experiment One Tolerance Data--

 Click on Table to Enlarge

Introduction

     This blog is being compiled as part of an ongoing assignment for Course EGR393  (Circuits Lab Course ID 22295824) being taught by Dr. Tolga Kaya at Central Michigan University during the Spring 2016 Semester.

It will document the work of Lab Team #4 consisting of Students Kevin Pawlak and Chris Ruby.

While this blog is can be viewed by the general public it's intended audience is Professor Kaya and possibly the other students in the course. 

Welcome to our Blog

Kevin Pawlak

Laboratory Team 4