Multimeter
Multimeter
Multimeters/Multi ohmmeters/Multitesters (referred to as 'meter') are versatile tools measuring (AC and DC) voltage (the voltmeter), current, and resistance.
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Applications and settings
Applications and settings
A multimeter has usually these standard settings to measure these values, represented as units' symbols:
DC current setting is represented as an 'A' with a horizontal line and a broken horizontal line. We can also DC current with a separate clamp ammeter. [2.1] Such symbol is also used on the label at the back of devices' (right images). A lot of meters have a separate input on the left for current testing. Often as it's fused in it must take different paths. There's a warning for the max current to test it on (often 10 A, with at times a 10 s duration).
If the limit is exceeded, the meter's fuse inside is damaged and the meter must be opened to replace the fuse.
[2.1] This device outputs 18 V DC current. Thus the device's battery reads 18 V via the meter, otherwise either the measured device or meter is malfunctuning.
[2.1] This one uses AC current
AC current setting is represented as an 'A' (for ampere) with a wave line.
[2.1] AC current is what's often used in house outlets. To measure one place both probes into the sockets and don't touch the probe after placing them in it. It's best to use only one hand to hold both probes as using both hand to hold both creates a live circuit with your body (chest) to let current flowing through and kill us. It'll read often 120 V in an outlet
Note: WARNING: Test outlets with high caution as the voltage can be fatal.
DC voltage setting is represented as a 'V' with a horizontal line and a broken horizontal line.
AC voltage setting is represented as an 'V' with a wave line.
Resistance setting is represented as an ohm symbol Ω (omega). [2.1] It measures how hard does it take for current to flow through a material.
[2.1] Measuring current across a copper wire reads ~0.1 V as current flows through copper.
[2.1] Across a rubber wire reads OL ("open loop) indicates infinite resistance as no current can flow across as to why rubber is used to insulate wires.
[2.1] But, measuring a resistor on a circuit can likely read a false value due to other paths of less resistances near it.
[2.1] Continuity settting is represented as an echo symbol. It allows us to locate connections to identify what connects to what by making a 'beep' sound, i.e., if a part has low enough resistance. E.g., Touching the 2 probes together makes the sound to confirm that the multimeter and probe have continuity and work fine.
This can be used for a big roll of wires, which can be impossible without it cutting it, unless
This also helps to find wire positions, i.e., which pin connects to which pin in a complex circuit e.g..
Capacitance setting is represented as a capacitor symbol. Be very vautious when using this setting to measure capacitors.
capacitor: energy-storing device for later uses.
Semiconductance is on the same range as the capacitance setting, represented as a generic diode symbol. [2.1] Measuring it in forward bias, with the black probe on the cathode (represented as a grey line) and the red probe on the side anode, should read ~0.7 V, the usual forward voltage drop. In reverse-bias (other way around), we should read OL. If we read values or no values in both direction than the diode is broken.
[2.1] An outlet measures ~60 Hz in North America
Frequency is represented as 'Hz', standing for Hertz, frequency's measurement unit ([2.1] like an electric generator's speed, i.e., the alternating wave's frequency).
A meter may also have a duty cycle, represented as a percentage % sign or 'duty', which tells what percentage of the time. So as an AC current goes, it often reads 50%
Power setting is represented as a 'W'.
Temperature setting is represented as a celcius, fahrenheit symbol, or a temperature symbol, a less common meter setting. [2.1] Meters with such features have a separate probe. The probe also shouldn't be wet if being used.
Hybrid parameter forward current gain common emitter setting is abbrevated/represented as 'hFE', another less common meter setting. [2.1] This is used for transistors and use an adapter IO probes in the input, and choose whether to use NPN or PNP transistor (look at the componet's datasheet)
On a live circuit, the resistance setting (Rx10) must never be used.
The "x10" means to multiply the needle's reading by 10.
Common issues
Common issues
If the meter reads 0 A current via the mA input no matter what but current reads normally on the 10 A input, what does that means?
The mA input and its fuse are damaged, unlike the 10 A input. As most meters have the 2 current inputs separated
A separate, fused mA/µA input (often a small, fast-blow fuse)
A separate 10 A input (often unfused or with a different fuse)
To fix the meter, open it and check/replace the mA fuse with the exact rating.
Related devices
Related devices
An oscilloscope (thought not a multimeter) is a "sophisticated" voltmeter measuring voltage, between 2 points in a circuit, telling the voltage difference, "push" forcing electrons to move in the circuit.
A galvanometer is a
An analog meter uses a needle to show the measured value.
analog: to use signals/info shown by variable physical quantity (position, voltage)
A digital meter shows values numerically on a screen digitally.
A voltmeter only measures voltage.
An ammeter measures current.
Special multimeters
Special multimeters
LCR Meter measures Inductance (L), Capacitance (C), and Resistance (R).
Fpr electronics design and repair.
An analog multimeter
Insulation tester tests insulation resistance (like a megohmmeter).
Earth ground tester measures grounding resistance in electrical installations.
Anmeter
Anmeter
An anmeter measures current (in amperes).
It's the setting on a multimeter that short-circuit a power source.
Parts
Parts
Turning on: Some multimeters have an 'on/off' switch/button. Some may have an auto-off function for battery saving, like a knob to rotate to set 'off' mode to turn off or to turn on by set the measurement unit (volt/current/power).
Symbols
Symbols
V-/V⎓ is for DC voltage.
V~/V≈ is for AC voltage.
Fig 1
Ports
Ports
Ports are jacks/holes to plug test leads/probes into multimeters to measure. Most have 2 ports, some 4.
lead/probe:
Common/Grounding port (black)
V Omega MA port is (red) tests most measurement.
400 mA port (Fig 1; red) is used less often.
300 mA port (red) measures 300 mA.
10 A port (Fig 1; red) is used less often.
It's the same for a analog meters.
Banana plugs
Banana plugs
Most multimeters have 2 banana plugs (1 red and 1 black) to connect ports.
A common plug (black) always goes into a common port and doesn't carry much electricity.
A positive/hot wire (red) plug goes into the property unit measured, for the voltage resistance/frequency.
Testing
Testing
Ohming out the leads is to test the probes are working internally: Plug the plugs into their respective probes and set the ohm mode with the kno.
Now tap the leads' needles together and the meter should read -0.5 Ω. If higher maybe replace them.
Measurement units
Measurement units
A wavy line '~' under a voltage symbol means AC current.
A straight line '-' under a voltage syrmbol means DC current.
Measuring
Measuring
To measure AC voltage, like an outlet, put the common plug into the big/left prong and the hot wire for the right/small prong--It should say ~120 V.
Ensure to disconnect the wires in the same order theyre pluggged.
To measure DC voltage, like a battery, put the common wire to the negative and hot wire to the positive pole.
Analog meter
Analog meter
Indicator zero connector
Indicatot pointer
Indicator scale
Continuity indicating
Range selector switch knob
0-ohms adjusting knob/0- centering meter (NULL meter) adjusting knob
Measuring Terminal +
8. Measurin Terminal - COM
9. Series Terminal Capacitor OUTPUT
10. Panel LED ( CONTINUITY
11. Rear Case
[8]
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.
Reading scales
Reading scales
Analog multimeters have often 3 scales, varying by order, but it's often at this order:
Ohms (Ω) scale: top
Voltage (V) scale, often shared between AC and DC: middle
Current (A) scale: bottom
Knobs
Knobs
The selection/function switch is (often) the center knob to select what range for the unit is measured.
Models like "Simpson" meters have:
10kV, 500V, 250V, 10V, 2.5V for the voltage range
500mA, 100mA, 10mA, 1mA for the ampere range
Rx1, Rx100, Rx10k for the resistance range
The DC and AC knob is (often) the left knob.
Some have a music note "♪", which means
Measuring ohms
Measuring ohms
The ohms scale (often top) goes from right (0 Ω) to left (infinity value), the opposite of voltage and ampere scales.
To measure ohms accurately, first calibrate the meter
(since the meter has a battery, which changes value it reads as it weakens): Set it on DC value (left knob).
Negative/positive doesn't matter here.
Set the range selector/selector (middle) switch highest range
10k Ω (middle knob) and touch the leads together.
We must zero it out by set the right knob to zero for the needle
to be at the right.
Measuring voltages
Measuring voltages
The voltage scale's (often middle) goes from right (0 V) to left.
For DC: Black probe is for negative point and red probe is positive (+) point.
For AC: Probe placement doesn’t matter.
Use the right scale to match the selected range.
If it's set at 25 V, it can measure ~0-25 V accurately.
Eg. 1# The selector switch is at the 25 V full scale position. How much voltage is read?
Method 1#
needle is at ~46V.
50 V is voltage's scale max value
Divide the range by the scale's max value: 25 ÷ 50 = 0.5
Multiply the the previous answer by 46: 0.5x46 = 23.1 V
So voltmeter reads 23.1 V.
Method 2#
We can also use the ohm scale: needle is at ~231.25 Ω.
250 Ω is the ohm scale's max value.
needle's value divide max value: 231.25/250 = 0.925
The range multiplies the previous answer: 0.925x25 = 23.1 V
Top scale = ohm
Middle scale = voltage
Bottom scale = current
Method 2#
As the meter is set at 25 V, it's also the full range and equals 250 on the meter, so 200 = 20 V.
10 ticks are between 200 and 250 and the voltage range is 5 V.
5/10 = 0.5 is the value per tick
From 200 to 250 is only, the needle is ~6.25, which times 5 V equals 3.125: 6.25x5 = 3.125.
Added to 20 V for the range of 0 to 200 gives 23.1 V.
Eg. 2# The selector switch is at the 5 V full scale position.
The needle is on ~16.5 V.
50 is the max scale
5/50 = 0.1
The voltmeter reads: 16.5x0.1 = 1.65 V
Eg. 3# The selector switch is at 25 V full scale position.
The needle is on ~33 V.
50 is the max scale
25/50 = 0.5
The voltmeter reads: 33x0.5 = 16.5 V
Measuring amperes
Measuring amperes
The current scale's (often bottom) goes from left (0 A) to right.
Measure ohms: By what we think the ohm value will be with the multipliers (Rx1, Rx100. Rx10k) around the middle knob, turn the knob to a multipler.
E.g. 1# If the needle is on on the 50 Ω and the range selector is on the Rx1k, , the voltmeter reads is 50x1k = 50k Ω
E.g. 2# If the needle is on on the 467 Ω and the range selector is on the Rx100, the voltmeter reads 467x100 = 46700 Ω
E.g. 3# This needle is on ~53 Ω and the selector switch is on 10k Ω.
So it reads 53x10k = 53k Ω
Assume the volt scale is the middle numbers.
References
References
[1]
[2] How to Use a Multimeter | The Home Depot - The Homet Depot (YouTube)
[2.1] How to use a multimeter like a pro, the ultimate guide - James Gatlin
[2.3] How to Read a Multimeter - How to Use an Analog Multimeter
[2.4] 01 Reading an Analog Meter - Academic Technology Lattc
[2.5] Analog Meter Reading
[2.6] Read an analog VOM meter
[2.7] How do you find voltage with an analog multimeter | Measure AC voltage using an analog multimeter
[5] Reading an Analog Ammeter and Voltmeter Problems - Weebly
[6] How to use and read a multimeter - Cellphone Repair Tutorials
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