Industrial Electricity Name Due next week (your lab time) Lab 1: Continuity, Resistance Voltage and Measurements Objectives: Become familiar with the terminology used with the DMM Be able to identify the symbols associated with the controls/jacks on the DMM Learn the basics of how to use a DMM to measure voltage, continuity and resistance Equipment: Digital Multimeter (DMM) Wire bundles Fuses Resistors AC/DC Power Supply Household wall adapter RESISTANCE MEASUREMENTS Continuity Testing Resistance is one of the three primary measurements made using a DMM. The others are voltage and current. One type of resistance measurement is called continuity testing. Continuity testing is useful to determine, for example, if fuses and switches are good or if a wire is broken (or to what component the wire is connected). When measuring continuity you are only interested in knowing if the resistance is zero (as in the case of a good fuse) or infinite (as in the case of a broken wire). On a DMM continuity can be measured by setting the meter on Ω. In this case the DMM s leads will be inserted into the jacks marked common (black lead) and Ω (red lead). Note that the jack marked Ω may have other markings as well such as ma and V. To measure ma or V, the knob would have to be rotated to the correct setting. Part 1: With the meter set to measure ohms and the leads in the correct jacks, touch the leads together. Ideally the measurement should be zero but may read a small amount of resistance due to the resistance of the wires making up the test leads. Remember that zero ohms (or near zero ohms) means there is continuity. Reading on meter (set to ohms) when the leads are NOT touching Reading on meter (set to ohms) when the leads are touching Don t be concerned if your meter did not give a perfect zero reading when the leads were touched together. With continuity testing we are only concerned with the extremes, that is, the readings very close to zero (when the leads are touching) and the reading when the leads are not touching. This is enough information to check and see if fuses are good or bad and if wires are broken or where a wire connects. 1
Part 2: READ CAREFULLY. Select TWO different wire bundles. Orient the bundle so that the arrow points to the right. Sketch them out below, including the wire colors and bundle number. Without resorting to drawing connecting lines, Indicate which wire (or wires) on the left are connected to which wire (or wires) on the right. LEFT SIDE RIGHT SIDE Bundle 1 Bundle 2 Part 3: Select six different fuses to determine which of them are good and which of them are bad. Record your findings below. Fuse # Good or Bad? In the space below, sketch the schematic symbol for A) a fuse, and B) a manual circuit breakere. 2
Resistor Testing Select a one of the protoboards that has resistors mounted on it. Complete the chart by following the directions below: Orient the board so that the tolerance bands are on your right (usually silver or gold) Starting from the left side of the resistor, write the exact color of each resistor s color bands Record the theoretical (nominal) value of each resistor based on the color code Compute the upper and lower limits of each of the nominal resistance values Measure the actual (true) resistance value of each resistor Put an X next to any entry where the measured resistance is out of tolerance range CARD # COLOR BAND Nominal Value Measured Value Lower Limit Upper Limit 1. 2. 3. 4. 5. In the space below, sketch the symbol for A) a fixed resistor, and B) a variable resistor. 3
VOLTAGE MEASUREMENTS CAUTION: If you attempt to measure voltage when the meter is set to measure ohms you may very well damage the meter. Set the meter now to measure voltage. In this part of the lab you will confirm that a power supply is working properly. The manufacturer of the power supply you will be testing states that the power supply is capable of supplying the following voltages: DC AC 5 Volts DC (fixed) 6.3 Volts AC 1.25 Volts DC to 15 Volts DC (variable) 12.6 Volts AC -1.25 Volts DC to -15 Volts DC (variable) 2.50 Volts DC to 30 Volts DC (variable) Though the actual values should be close to the specifications, they will vary somewhat. Complete the table below based on your measured values. SUPPLY # IMPORTANT NOTES When measuring DC, make sure the meter is set to measure DC volts Connect the black lead of the DMM to the black post except when measuring 0 to 30 volts When measuring AC, make sure the meter is set to measure AC volts Connect the black lead of the DMM to the black post except when measuring 12.6 volts DC MEASUREMENTS AC MEASUREMENTS Specifications 5 Volts (fixed) 1.25V to 15V -1.25V to -15V 2.50 V to 30 V 6.3 V 12.6 V Measured Reading to to to Note: You should be writing in a range of values in boxes 2, 3, & 4 Select another power supply (AC adapter) and measure its output voltage. Record your findings below. Brand Model Rated output voltage Measured output voltage There are (at least) two ways to determine the polarity of the adapter. What are they? 4
Review questions. Please write your responses clearly and completely. 1. What are the three primary measurements made with a DMM? A) B) C) 2. Sketch and label the schematic symbols for each of the circuit parameters from question 1 that have a schematic symbol. Note: the schematic symbols are not the symbols from the front of the DMM. 3. A) What does it mean for a component to exhibit continuity? B) When measuring continuity with a meter, you are measuring a subcategory of which of the parameters from question 1. 4. A) What is meant by the nominal value of a resistor? B) How is the nominal value of a resistor determined? C) Why is the actual value of a resistor almost always different than the nominal value? 5. When measuring the resistance of a load, the meter must be set to measure resistance and set to the proper scale. To insure an accurate measurement and to avoid potential harm (to equipment & technician) it is essential that you do two other things when making this measurement. What are they? A) B 6. If you were handed a switch (think simple wall switch used to turn a light on and off), explain how you could use a DMM to determine if it the switch s internal contacts are open or closed. Draw the schematic symbol for a SPST switch. 5