MULTIMETERS Flashcards
What are the two basic types of multimeters?
Analog and digital
Describe the basic operating principle of an analog multimeter?
The multimeter takes the energy from the circuit under test and converts that energy into a magnetic field and the magnetic field is determine by the amount of variable current in the circuit
Mulimeters are capable of measuring what three electrical characteristics?
Voltage, Ampere and Resistance.
What are two disadvantages of an analog multimeter
Fragile and interpretation
What term is used to describe the calibrated resistance that is placed in series with a multimeters leads in order extend the useful range of a multimeter when measuring voltage?
V” Multiplier
What term is used to describe the calibrated resistance that is placed in parallel with a multimeters leads in order to extend the useful range of a multimeter when measuring current?
Shunt.
What are two advantages of a digital multimeter?
No interpretation errors and autorange
Prior to making resistance measurements in an electrical circuit, the power should be turned
___off______.
What should be checked prior to using a multimeter
- Check calibration.
- Inspect, check for damages and condition.
- Setup, set the right function range and connections.
- Choose scale.
- Zero meter.
- Zero ohm adjustment when making resistance measurements
How often does a multimeter require calibration?
Requires a annual calibration.
1What is the source of power/current when making resistance measurements?
The battery in multimeter.
The operation of an analog multimeter is based upon what principle?
Base on permanent mag field and electromagnetic mag field produced from the current flowing in the circuit.
If you are not sure of the value you are measuring, what setting/range should you start with?
Start with highest range first to avoid any damage in multimeter
List the steps for properly setting up your multimeter for measuring AC.
Select the AC function in multimeter
Describe how current is measured
Current is measured with an ammeter connected in the current path by braking the circuit and inserting the meter in series, the positive side or lead should be connected towards the positive voltage source, the meter should not affect the current however the internal resistance in the meter may have some effect in the reading but is significantly small.
Describe how voltage is measured
Voltage is measured with a Voltmeter, polarity must be correct when placing the probes across any component before making any measurements red lead should be connected to positive jack and black lead should be connected in the negative jack of voltmeter same when taking measurements on the components the polarity should match the component, this will prevent a incorrect reading or damage
Describe how resistance is measured.
Resistance is measured with the ohmmeter, first the leads should be connected in the correct jacks of ohmmeter, the meter must be adjusted before use and should be zeroed before each use, power in the circuit must be turn off, then a constant current power by the battery meter is passed through the resistance that’s being tested and the ohmmeter measure the voltage across the resistance.
How much resistance is need it for continuity test
15 ohms
Factor to consider making a measurement
Circuit on or off, E is measured in a parallel. I and R are measured in series
computing funtions for DMM
Input, decision, memory, output,
logic AND OR NOT
What must be known prior making measurements with MM
What values will be measuring
MM specifications
Manual ranging, limit, max and extended and minimum readings
Voltage and current must be measured with power
ON
Resistance and continuity must be measured with power
OFF
DMM types
Ranging and autoranging
DMM advantages
No intepretation errors
easy set up
easy operation
Rugged
DMM tips for leads
Contact, scratch and press
Basic analog MM parts
Display, funtion,connectors, test leads
Analog MM caracteristics
Infinitely variables scale
moving parts
Basic operation interaction of two magnetic fields
Analog MM funtion
A mag field is produced by a MM permanent magnet and a mag filed produced from “I” flowing in the circuit under test variables of electromagnetic
Disadvantages of analog MM
Fragile
interpretation
errors
required effort
FAA 4 checks
Visual
functional
operational
Bench
MM set up
Inspect select function/range connect probes prepare circuit under test make measurements
Requirements for a MM
Capabilities
consistancy
reliability
Rheostat
Has 2 connection points examples light dimmer, panel, radios Rheostat drops voltage
Potentiometer
Has 3 connections example a volumen control in a radio Potentiometer divides voltage
