Introduction
The most important debugging tool in any E.E.'s toolbox is a trusty multimeter. A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature, etc.
Kinds of Multimeter :-
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1-Analog multimeter
Analog multimeters, although older than the commonly preferred digital multimeter, do come with several unique advantages. Although both digital and analog multimeters measure varying units, such as voltage, current, and resistance, they display their readings in distinctly different ways.
Analog multimeters, do take some energy from the circuit they are testing, whereas digital multimeters operate independent of circuit energy. In order to give an accurate reading analog multimeters need a high level of sensitivity—otherwise, the results may be skewed. When testing for resistance, the multimeter can rely on battery power.
Ranges for typical analog multimeter use varies with each application: For DC voltage, 0.5 V, 2.5V, 10V, 50V, 250V, 1000V are all standard range settings. For AC voltage, 10V, 50V, 250V, and 1000V are standard settings. Current is measured in amperes, with standard DC settings of 2.5, 25, and 250 amperes. AC current is hardly ever measured. Resistance, measured in ohms, has standard settings around 20, 200, 2000, 20,000, and 200,000 ohms. When not in use, leaving the multimeter around 10V is not a bad idea, because misusing the multimeter at this level is not likely to cause much damage.
HOW TO USE MULTIMETER,
1.) Indicator Zero Connector 7.) Measuring Terminal +
2.) Indicatot Pointer 8.) Measurin Terminal - COM
3.) Indicator Scale 9.) Series Terminal Capacitor OUTPUT
4.) Continuity Indicating 10.) Panel
LED ( CONTINUITY ) 11.) Rear Case
5.) Range Selector Switch knob
6.) 0-ohms adjusting knob
/0- centering meter
(NULL meter) adjusting knob
1.) Resistance (OHMS) scale
2.) DCV, A scale and ACV scale (10V or more)
3.) 0-centerig (NULL) +/- DCV scale
4.) ACV 2.5 (AC 2.5V) exclusive scale
5.) Transistor DC amplification factor (hFE) scale
6.) 1.5 baterry test (BATT 1.5V)
7.) OHMS range terminal to terminal current (Li) scale)
8.) OHMS range terminal to terminal voltage (LV) scale
9.) Decibel (dB) scale
10.) Continuity Indicating LED
11.0 Mirror: To obtain most accurate readings,
the mirror is deviced to make operator eyes, the indicator pointer, and the indicator pointer reflexed to the mirror put together in line.
How to Measure Resistance
If a lot of electricity flows, that means the object has very little electrical resistance, while if hardly any electricity flows, that means the object has very high electrical resistance. The multimeter measures the electrical current flow, and uses this to calculate the resistance of the object in units called “Ohms”. So, turn the settings selector on your multimeter to measure resistance. First, check the calibration of your multimeter. With the probes not touching each other, the reading should be “infinite resistance”, meaning no electricity is flowing. When you touch the probes together, the multimeter should read zero resistance, meaning that the current is flowing through the probes as quickly and easily as possible.
Now, we are ready to make some measurements.
First, check a metal object: the resistance should be very close to zero ohms because metals are very good conductors of electricity.
Next, plastic or wood: the resistance should be extremely high, because these are all very bad conductors of electricity (insulators).
Now try the pencil: touch the multimeter probes to the lead on each end of the pencil. You should get a reading of somewhere around 10 to 100 ohms. This means that the pencil lead (graphite) will conduct electricity, but that it is not as good of a conductor as most metals.
Finally, try yourself: grab hold of one probe in each hand, and see what your resistance is (don’t worry, the battery in the multimeter is not strong enough to give you a shock). If your hands are dry, you will probably have nearly infinite resistance. If your hands are sweaty, or if you lick your fingertips before taking hold of the probe, you should have
a resistance somewhere around 50,000 ohms. If you touch the probes to your tongue, the resistance should be much lower.
So, this means that while your body has a lot of resistance, it has less resistance than an insulator like a piece of wood. This is why you can get electrically shocked (because electricity can flow through your body), and why electrical appliances near water are a bad thing (because if you are wet, you have a lot less electrical resistance than if you are
dry).
Read the indicated code value indicated in Schematic Diagram then select the Ohm-scale within but not way below the indicated value. A resistor is good if its resistance is close to the indicated value.Tolerance should be considered with the ohmmeter reading. While, no resistance reading at all on the ohmmeter scale settings means that the resistor is open. A zero resistance reading on all ohmmeter scale settings means that the resistor is shorted.
How to Measure Voltage
Set the meter for the highest range provided for AC Volts. Many times, the voltage to be measured has a value that is unknown. For this reason, the highest range possible is selected so that the meter circuitry and movement will not be damaged by voltage greater than expected. If the meter were set to the 50 volt range and a common U.S. electrical outlet were to be tested, the 120 volts present could irreparably damage the meter.
Insert the black probe in the "COM" or "-" jack.
Insert the red probe in the "V" or "+" jack.
Locate the Voltage scales. There may be several Volt scales with different maximum values.
How to Measure Current Amperes
Determine if AC or DC by measuring the voltage of the circuit as outlined above.
Set the meter to the highest AC or DC Amp range supported. If the circuit to be tested is AC but the meter will only measure DC amps (or vice-versa), stop. The meter must be able to measure the same mode (AC or DC) Amps as the voltage in the circuit, otherwise it will indicate 0.
Be aware that most multimeters will only measure extremely small amounts of current, in the uA and mA ranges. 1 uA is .000001 amp and 1 mA is .001 amp. These are values of current that flow only in the most delicate electronic circuits, and are literally thousands (and even millions) of times smaller than values seen in the home and automotive circuits that most homeowners would be interested testing. Just for reference, a typical 100W / 120V light bulb will draw .833 Amps. This amount of current would likely damage the meter beyond repair. A "clamp-on" type ammeter would be ideal for the typical homeowner requirements, and does not require opening the circuit to take measurements (see below). If this meter were to be used to measure current through a 4700 ohm resistor across 9 Volts DC, it would be done as outlined below:
Insert the black probe into the "COM" or "-" jack.
Insert the red probe into the "A" jack.
Shut off power to the circuit.
Open the portion of the circuit that is to be tested (one lead or the other of the resistor). Insert the meter in series with the circuit such that it completes the circuit. An ammeter is placed IN SERIES with the circuit to measure current. It cannot be placed "across" the circuit the way a voltmeter is used (otherwise the meter will probably be damaged). Polarity must be observed. Current flows from the positive side to the negative side. Set the range of current to the highest value.
Apply power and adjust range of meter downward to allow accurate reading of pointer on the dial. Do not exceed the range of the meter, otherwise it may be damaged. A reading of about 2 milliamps should be indicated since from Ohm's law I = V / R = (9 volts)/(4700 Ī©) = .00191 amps = 1.91 mA.
If you're measuring the current consumed by the device itself, be aware of any filter capacitors or any element that requires an inrush (surge) current when switched on. Even if the operating current is low and within the range of the meter fuse, the surge can be MANY times higher than the operating current (as the empty filter capacitors are almost like a short circuit). Blowing the meter fuse is almost certain if the DUT's (device under test) inrush current is many times higher than the fuses rating. In any case, always use the higher range measurement protected by the higher fuse rating (if your meter has two fuses), or just be careful.
2.) Indicatot Pointer 8.) Measurin Terminal - COM
3.) Indicator Scale 9.) Series Terminal Capacitor OUTPUT
4.) Continuity Indicating 10.) Panel
LED ( CONTINUITY ) 11.) Rear Case
5.) Range Selector Switch knob
6.) 0-ohms adjusting knob
/0- centering meter
(NULL meter) adjusting knob
2.) DCV, A scale and ACV scale (10V or more)
3.) 0-centerig (NULL) +/- DCV scale
4.) ACV 2.5 (AC 2.5V) exclusive scale
5.) Transistor DC amplification factor (hFE) scale
6.) 1.5 baterry test (BATT 1.5V)
7.) OHMS range terminal to terminal current (Li) scale)
8.) OHMS range terminal to terminal voltage (LV) scale
9.) Decibel (dB) scale
10.) Continuity Indicating LED
11.0 Mirror: To obtain most accurate readings,
the mirror is deviced to make operator eyes, the indicator pointer, and the indicator pointer reflexed to the mirror put together in line.
How to Measure Resistance
If a lot of electricity flows, that means the object has very little electrical resistance, while if hardly any electricity flows, that means the object has very high electrical resistance. The multimeter measures the electrical current flow, and uses this to calculate the resistance of the object in units called “Ohms”. So, turn the settings selector on your multimeter to measure resistance. First, check the calibration of your multimeter. With the probes not touching each other, the reading should be “infinite resistance”, meaning no electricity is flowing. When you touch the probes together, the multimeter should read zero resistance, meaning that the current is flowing through the probes as quickly and easily as possible.
Now, we are ready to make some measurements.
First, check a metal object: the resistance should be very close to zero ohms because metals are very good conductors of electricity.
Next, plastic or wood: the resistance should be extremely high, because these are all very bad conductors of electricity (insulators).
Now try the pencil: touch the multimeter probes to the lead on each end of the pencil. You should get a reading of somewhere around 10 to 100 ohms. This means that the pencil lead (graphite) will conduct electricity, but that it is not as good of a conductor as most metals.
Finally, try yourself: grab hold of one probe in each hand, and see what your resistance is (don’t worry, the battery in the multimeter is not strong enough to give you a shock). If your hands are dry, you will probably have nearly infinite resistance. If your hands are sweaty, or if you lick your fingertips before taking hold of the probe, you should have
a resistance somewhere around 50,000 ohms. If you touch the probes to your tongue, the resistance should be much lower.
So, this means that while your body has a lot of resistance, it has less resistance than an insulator like a piece of wood. This is why you can get electrically shocked (because electricity can flow through your body), and why electrical appliances near water are a bad thing (because if you are wet, you have a lot less electrical resistance than if you are
dry).
Read the indicated code value indicated in Schematic Diagram then select the Ohm-scale within but not way below the indicated value. A resistor is good if its resistance is close to the indicated value.Tolerance should be considered with the ohmmeter reading. While, no resistance reading at all on the ohmmeter scale settings means that the resistor is open. A zero resistance reading on all ohmmeter scale settings means that the resistor is shorted.
How to Measure Voltage
Get into the right mode
There are often two seperate modes for AC and DC voltage. Both will have a V but one will have two lines, one dashed and one solid (DC) and one with have a wave next to it (AC).Set the meter for the highest range provided for AC Volts. Many times, the voltage to be measured has a value that is unknown. For this reason, the highest range possible is selected so that the meter circuitry and movement will not be damaged by voltage greater than expected. If the meter were set to the 50 volt range and a common U.S. electrical outlet were to be tested, the 120 volts present could irreparably damage the meter.
Insert the black probe in the "COM" or "-" jack.
Insert the red probe in the "V" or "+" jack.
Locate the Voltage scales. There may be several Volt scales with different maximum values.
How to Measure Current Amperes
Determine if AC or DC by measuring the voltage of the circuit as outlined above.
Set the meter to the highest AC or DC Amp range supported. If the circuit to be tested is AC but the meter will only measure DC amps (or vice-versa), stop. The meter must be able to measure the same mode (AC or DC) Amps as the voltage in the circuit, otherwise it will indicate 0.
Be aware that most multimeters will only measure extremely small amounts of current, in the uA and mA ranges. 1 uA is .000001 amp and 1 mA is .001 amp. These are values of current that flow only in the most delicate electronic circuits, and are literally thousands (and even millions) of times smaller than values seen in the home and automotive circuits that most homeowners would be interested testing. Just for reference, a typical 100W / 120V light bulb will draw .833 Amps. This amount of current would likely damage the meter beyond repair. A "clamp-on" type ammeter would be ideal for the typical homeowner requirements, and does not require opening the circuit to take measurements (see below). If this meter were to be used to measure current through a 4700 ohm resistor across 9 Volts DC, it would be done as outlined below:
Insert the black probe into the "COM" or "-" jack.
Insert the red probe into the "A" jack.
Shut off power to the circuit.
Open the portion of the circuit that is to be tested (one lead or the other of the resistor). Insert the meter in series with the circuit such that it completes the circuit. An ammeter is placed IN SERIES with the circuit to measure current. It cannot be placed "across" the circuit the way a voltmeter is used (otherwise the meter will probably be damaged). Polarity must be observed. Current flows from the positive side to the negative side. Set the range of current to the highest value.
Apply power and adjust range of meter downward to allow accurate reading of pointer on the dial. Do not exceed the range of the meter, otherwise it may be damaged. A reading of about 2 milliamps should be indicated since from Ohm's law I = V / R = (9 volts)/(4700 Ī©) = .00191 amps = 1.91 mA.
If you're measuring the current consumed by the device itself, be aware of any filter capacitors or any element that requires an inrush (surge) current when switched on. Even if the operating current is low and within the range of the meter fuse, the surge can be MANY times higher than the operating current (as the empty filter capacitors are almost like a short circuit). Blowing the meter fuse is almost certain if the DUT's (device under test) inrush current is many times higher than the fuses rating. In any case, always use the higher range measurement protected by the higher fuse rating (if your meter has two fuses), or just be careful.
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