Introduction to Introduction to Digital MultimetersDigital Multimeters

What do meters measure?What do meters measure?

A meter is a measuring instrument. A meter is a measuring instrument. An An ammeterammeter measures current. measures current.A A voltmetervoltmeter measures the potential measures the potential difference (voltage) between two points.difference (voltage) between two points.An An ohmmeterohmmeter measures resistance. measures resistance. A A multimetermultimeter combines these functions, combines these functions, and possibly some additional ones as well, and possibly some additional ones as well, into a single instrument.into a single instrument.

Multimeters measureVoltage V

Amperage AResistance Ω

and tests for continuity

Selector switch

Note the off position.Turn off your meter when not in use.

Simple circuitSimple circuit

Multimeter as a VoltmeterMultimeter as a Voltmeter

To use a multimeter as a voltmeter it is connected in To use a multimeter as a voltmeter it is connected in parallelparallel between the two points where the between the two points where the measurement is to be made. measurement is to be made.

The voltmeter provides a parallel pathway so it needs The voltmeter provides a parallel pathway so it needs to be of a high resistance to allow as little current to be of a high resistance to allow as little current flow through it as possible.flow through it as possible.

Select AC or DC voltage measurement.

Select AC or DC voltage measurement.

Select AC or DC voltage measurement.

Mutimeter as a VoltmeterMutimeter as a Voltmeter

Select the DC or AC VoltsSelect the DC or AC Volts

Start at the highest volts scale and work Start at the highest volts scale and work your way down. your way down.

Probe leads are connected in Probe leads are connected in parallelparallel..

Be very careful to not touch any other Be very careful to not touch any other electronic components within the electronic components within the equipment and do not touch the metal tips.equipment and do not touch the metal tips.

Mutimeter as a VoltmeterMutimeter as a Voltmeter

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

measuring voltagemeasuring voltage

Multimeter as a AmmeterMultimeter as a Ammeter

Turn Power Off before connecting Turn Power Off before connecting multimeter.multimeter.Break Circuit.Break Circuit.Move multimeter leads (if needed).Move multimeter leads (if needed).Place multimeter in series with circuit.Place multimeter in series with circuit.Select highest current setting, turn power Select highest current setting, turn power on, and work your way down.on, and work your way down.Turn power off.Turn power off.Disconnect multimeter. Disconnect multimeter. Reconnect CircuitReconnect Circuit

Ammeter mode measures current in Amperes. To measure current you need to Ammeter mode measures current in Amperes. To measure current you need to power off the circuit, you need to power off the circuit, you need to break the circuitbreak the circuit so that the ammeter can be so that the ammeter can be connected in connected in seriesseries. All the current flowing in the circuit must pass through the . All the current flowing in the circuit must pass through the ammeter. Meters are not supposed to alter the behavior of the circuit, so the ammeter. Meters are not supposed to alter the behavior of the circuit, so the ammeter must have a very LOW resistance. The diagrams below show the ammeter must have a very LOW resistance. The diagrams below show the connection of a multimeter to measure current. connection of a multimeter to measure current.

A

Multimeter as a OhmmeterMultimeter as a Ohmmeter

Power always has to be offPower always has to be off

Component has to be removed from Component has to be removed from circuitcircuit

Start at lowest Ohm setting or maybe Start at lowest Ohm setting or maybe highest.highest.

Component being measured Component being measured needs to be removed from the needs to be removed from the

circuit.circuit.

Multimeter as a OhmmeterMultimeter as a Ohmmeter

Multimeter as a OhmmeterMultimeter as a Ohmmeter

Multimeter as a OhmmeterMultimeter as a Ohmmeter

Multimeter as a OhmmeterMultimeter as a Ohmmeter

Multimeter as a OhmmeterMultimeter as a Ohmmeter

ReviewReview

A meter capable of checking for voltage, current, and A meter capable of checking for voltage, current, and resistance is called a resistance is called a multimetermultimeter, , As voltage is always relative between two points, a As voltage is always relative between two points, a voltage-measuring meter ("voltmeter") must be voltage-measuring meter ("voltmeter") must be connected to two points in a circuit in order to obtain a connected to two points in a circuit in order to obtain a good reading. Be careful not to touch the bare probe tips good reading. Be careful not to touch the bare probe tips together while measuring voltage, as this will create a together while measuring voltage, as this will create a short-circuit! short-circuit! Remember to always check for both AC and DC voltage Remember to always check for both AC and DC voltage when using a multimeter to check for the presence of when using a multimeter to check for the presence of hazardous voltage on a circuit. Make sure you check for hazardous voltage on a circuit. Make sure you check for voltage between all pair-combinations of conductors, voltage between all pair-combinations of conductors, including between the individual conductors and ground! including between the individual conductors and ground!

ReviewReview

When in the voltage-measuring ("voltmeter") mode, When in the voltage-measuring ("voltmeter") mode, multimeters have very high resistance between their multimeters have very high resistance between their leads. leads. Never try to read resistance or continuity with a Never try to read resistance or continuity with a multimeter on a circuit that is energized. multimeter on a circuit that is energized. Current measuring meters ("ammeters") are always Current measuring meters ("ammeters") are always connected in a circuit so the electrons have to flow connected in a circuit so the electrons have to flow throughthrough the meter. the meter. When in the current-measuring ("ammeter") mode, When in the current-measuring ("ammeter") mode, multimeters have practically no resistance between their multimeters have practically no resistance between their leads. This is intended to allow electrons to flow through leads. This is intended to allow electrons to flow through the meter with the least possible difficulty. If this were not the meter with the least possible difficulty. If this were not the case, the meter would add extra resistance in the the case, the meter would add extra resistance in the circuit, thereby affecting the current. circuit, thereby affecting the current. Turn selector to off when not in use.Turn selector to off when not in use.

Turn selector to off when not in use.