Module 2: Electrical Measurements
Types of electrical circuits
*Series Circuit *Parallel Circuit
Voltage Points
2 points are needed to measure voltage b/c voltage is the difference b/w the potential of 2 points in an electrical circuit. example: the circuit shown here, a power supply provides a source of both high & low potential
Using DMM (digital multimeter) to test Continuity
A DMM can be used to test for continuity, sometimes in more than 1 way. Two methods are 1) Measuring Resistance 2) Using a Continuity Tester
Parallel circuit
A circuit that contains more than one path for current flow. The current flows from the positive terminal through the circuit until it reaches back until it reaches node 1, where it splits the current b/w branch A & branch B The 2 branch currents than rejoin each other at node 2 & flow back to the power supply's negative terminal
Force
A push or pull exerted on an object; is what causes the object to move is not the value but the force on it, but the difference b/w them
measuring resistance
Everything has a very small resistance value such as .01 ohms. If a conductor has continuity, the display shows a very small resistance value such as .01 ohms If display shows an out of ranger indication on a very large scale, there is an open in that conductor and there is no continuity, An open has infinite resistance
Example of a circuit connected in series
Example: Holiday lights; 1 blew out they were all out
Applications of a Series & Parallel Circuit
Most circuits in commercial & residential buildings are wired in parallel. Therefore, all of the outlets & sockets do not require something to be plugged into them to complete the circuit
Voltage Comparisons
Most voltage comparison will only use one of the 2 methods: 1) compare the points to a common reference of know value (e.g. A to C) 2) Measure the voltage across the component (e.g. A to B)
Difference in potential: Point B
Point B is somewhere b/w A & C in potential b/c it is separated by a resistor on each side
Units of measurement for voltage
Volt is represented by either E (electromotive force) or V (voltage). Example: 20 Volts = 20 V
Voltmeter Leads
With an analog multimeter, attach the red(+) lead to the higher potential point & the black (COM) lead to the lower potential point; otherwise the meter will get damaged.
Description of a Voltmeter
a device that measure the voltage b/w 2 points in an electrical circuit.
Types of Multimeter
a device that measures (V), current , & resistance; there are analog display and digital display
Definition of an Ammeter
a device that measures electrical current. It can have an analog display, like the one in the graphic, or a digital display
Schematic Symbol for a Volmeter
a key tool for troubleshooting & analysis or circuits. In some cases, schematic diagrams may even show specify a voltmeter as part of the circuit. example: the graphic shows the electrical schematic symbol for a voltmeter
Continuity
a situation in which there is a continuous or complete path for current flow in an electrical circuit. since all electrical components in a circuit are connected with a conductor of some kind, wires must have continuity or the circuit will not operate. Continuity does not represent 0 resistance. Even a short wire contains some resistance
Schematic Symbol for an Ammeter
ammeters are often specified in circuits. The graphic shows the schematic symbol for ammeter
Voltage Reference Points
any point in the circuit can be a reference. Placing the common DMM lead at a point in the circuit makes that the reference, & all voltages are then measured & indicated relative to that point
Analog Multimeter
are used when there are very fast changes in a reading b/c the needle responds faster than a digital readout
Voltage
causes electrons to move (flow) in an electrical circuit voltage; another name for voltage is electromotive force. As with any force, this voltage value is measured as a difference (force) b/w 2 points
Example of a circuit connected in parallel
if loads are connected in parallel & one fails, the others will continue to work. This is b/c the same current does not flow through each branch. For this reason, newer strings of holiday lights are connected in parallel.
Current Direction
if the COM lead is placed on a lower potential point in the circuit, a positive current is indicated. If the COM lead is placed on a higher potential point in the circuit, a negative current is indicated. The negative current is indicated. The negative does not only a lower amount of current. It only indicates the direction of current flow
Measuring the Resistance of a Component
if the component is connected in a circuit, you have to take resistance measurements with the power to the circuit turned off to get an accurate measurement. In this case, the ohmmeter is measuring the resistance of resistor R1 notice that the resistor R1 is not connected in a circuit. You can measure the resistance of any component this way. Also, it does not matter how the leads are connected to the component since resistance has no polarity.
Current Flow
in a series circuit flows from the (+) terminal of the power supply to the (-) terminal through each component in the circuit.
Definition of Schematic symbol of an Ohmmeter
is a device that measures the resistance b/w 2 points in an electrical circuit.
AC (alternating current) voltage
is called alternating current flow Example: 240 Volts Alternating Current = 240 VAC 5 Volts Alternating Current = 5VAC
Using a Continuity tester
it indicates continuity with a buzzing sound, when you you place the leads across a conductor or a component, a beeping or buzzing sound is made by the continuity tester
Characteristics of a circuit connected to a series
it is common to connect input devices in series. it is not common to connect loads in series. One reason is that if one of the load fails while the circuit is in operation, all of the loads will lose power.
DC (direct current) Voltage
it's called direct current flow Tip: when only the V is used is understood as DC Example: 20 Volts Direct Current = 20 VDC 5 Volts Direct Current = 5 VDC
Voltmeter ranges
most voltmeter have range switches that allow you to select the voltage range that you want to measure Tip: all (V) measurements should be measured from lowest (V) to get better accuracy. However is a good practice to measure from the highest (V) range setting 1st & switch to lower (V) ranges to get more accurate readings. It also help to protect meter from damage
series circuit
one in there is only 1 path for current travel The total current in a series circuit flows through each component. It starts at the positive terminal of the power supply & flows though 1 component after the other & then back to negative terminal of the power supply
Difference in potential: Point A
point A is the point of highest potential b/c it is closest to the high potential terminal of the power supply
Difference in potential: Point C
point C is the point of the lowest potential b/c it is closest to the low potential side of the power supply
Digital Multimeter (DMM)
readings of a (DMM) are much easier to read b/c they are displayed in digital format.
Units of Measurement for Current
sometimes current values can be very small such as 1/1000th of an amp (0.001A) in this case the unit used is in milliamp or mA
Example of Voltage in a Parallel Circuit
the (V) at points 1,2, & 3 referenced to a ground are equal since they are actually the same point. The same is true for points 4,5,& 6 this means that the (V) drop across each branch in a parallel circuit is always the same, the (V) drop is 10 V
Voltage Drop Descriptions
the (V) drop across any component is the difference in (V) referenced to ground b/w the 2 terminals of the component Example: the (V) drops across load 1 is 4 (V) b/c the (V) at its 2 terminals referenced to the ground are 10volts & 6 volts The amount of (V) that is used by each load ( its voltage drop) depends on the resistance of each load.
Measuring Voltage from different points
the actual voltage measured at any point depends on what other point you use as a reference example: if you measure b/w points A &C, you will get a higher value than measuring b/w points A & B b/c point A is farther from C than B is potential
Characteristics of a circuit connected in parallel
the current in a parallel circuit is divided among the branches of the circuit. The amount of current that flows in each branch depends on the amount of resistance in the branch.
Difference in potential
the difference in potential (voltage) from 1 side of the power supply to the other is the force that causes current to the flow. There are 3 points of interest in this circuit: *Point A *Point C *Point B
Definition of Current
the flow of electrons through a circuit. It carries the electrical energy to the point of use. current can either flow in 1 direction (DC) or alternately in 2 directions (AC) Current is measured in units of amperes (amps). The abbreviation symbol (amps) is an A following numeric value. For example of 5 amperes is written as 5 A
Definition of resistance
the measure of a component's ability to resist the flow of current in a circuit. When current passes through a component that has resistance, the current decreases
Voltage in a series circuit
the total (V) supplied by the power supply is divided among the loads. As shown here each load in the circuit uses a certain among of the (V) as the current travels through it. This leaves less (V) available for the next load to use
Unit of measurement for Resistance
the unit of measure for resistance are ohms.
Measure Resistance of a Circuit
to measure a component when it is connected in a circuit, you should always turn off the power & disconnect 1 terminal of the component from the circuit. Otherwise, you will get erroneous resistance measurement
Measuring Current with an Ammeter
to measure current through a component , the ammeter is placed in series with the component, as shown in the graphic. This is different than measuring (V) where a meter leads are connected across the component (in parallel)
Measuring Resistance with an Ohmmeter
to measure resistance, the test leads of the ohmmeter are placed in parallel with the component to be measured. the test lead connections for measuring resistance are the same as for meaning voltage. You measure across the component. It doesn't matter which lead is connected to each side of the component
Voltage in Parallel Circuit
when a parallel circuit is connected to a constant (V) power supply, the same amount of (V) is available for each 1 of the branches of the circuit.
Voltage Magnitude Comparison
when comparing the relative sizes of the voltage in a circuit, only compare the magnitudes of the voltage. Example: A negative (V) should not necessarily be considered a smaller (V)than a positive voltage. The (V) with the smaller magnitude is the smaller potential. If both (V) are negative , the one with smaller magnitude is the smaller potential
Resistance Characteristics of a Load Connected Series
when load are connected in a series, their individual resistance add together to increase the total resistance in the circuit as shown here, the resistance of the circuit is larger with 3 resistors in series than just 2 resistor
Resistance Characteristics of a Load Connected Parallel
when loads are connected in parallel, the total amount of resistance actually decreases when more resistors are added. As shown here, the total resistance of three 10 ohms resistors in parallel is only 3.33 ohms while the resistance of 1 resistor is 10 ohms.
