# MULTIMETER

A multimeter is an electronic measuring device used to measure mostly voltage (alternating and direct in volts), resistance (in ohms) and current (alternating and direct in amperes) in electronics & electrical equipment. A multimeter is otherwise known as a VOM (Volt-Ohm meter or Volt-Ohm milliammeter ) or multitester.  It  is  also  used to  test  continuity  between two  points  to  confirm  if there is any breaks in a circuit. Furthermore, some multimeters measure:

Capacitance in farads ,Conductance in Siemens , Frequency in hertz , Inductance in henries, temperature in degrees Celsius or Fahrenheit , Diodes (measuring forward drop of diode Junctions), and transistors (measuring current gain and other parameters).

A multimeter is very useful in finding faults and be used to troubleshoot electrical or electronic problems.

## How To Use A Multimeter

Before making any measurement you need to know what you want to test. If you are measuring voltage, select the AC range (200v, 250v, 750v, or 1000v) or DC range (200mv, 2000mv, 10v, 20v, 200v, or 1000v).  If you are measuring resistance, select the Ohms range (200, 2000, x10k, 20k, 200k or 2000k).  Whatsoever measurement you to check , you need to select the appropriate function and range

Learning to use a multimeter is very important especially if you want to repair or build electronic. The method of use of a multimeter is the same irrespective of the types (Analog and Digital).

Measuring Voltage

• Voltage is divided into 2 sections AC & DC.Alternating Current (AC) is house voltage (110vac or 240vac) Direct Current (DC) is battery voltage.
• When you want to measure voltage always switch the multimeter to a value higher than your expected value.
• Be  very  cautious  to  not  touch  any  other  electronic  components within  the  equipment  and do  not  touch  the  tips  to  each  other  while connected to anything else.
• To measure  voltage connect  the  leads  in  parallel  between  the  two points  where  the  measurement  is  to  be  made.  The  multimeter provides a  parallel  pathway  so  it  needs  to be  of  a high resistance to  allow  as  little  current  flow  through  it  as  possible.

Measuring Resistance

• Resistance (W) is the opposition to current
• Resistance is measured in Ohm’s
• Disconnect power source before testing
• Remove component or part from system before testing. If any voltage is present; the value of resistance will be incorrect.
• In most cases you cannot measure a component while it is in-circuit. This is because the meter is actually measuring a voltage across a component and calling it a “resistance.” The voltage comes from the battery inside the meter.  If any other voltage is present, the meter will produce a false reading. If you are measuring the resistance of a component while still “in circuit,” (with the power off) the reading will be lower than the true reading.
• Measure using lowest value, if OL move to next level

Measuring Current

• Current (amps) is the flow of electrical charge though a component or conductor.
• Current is measured in amps or amperes
• Current is always measured when the circuit is working (i.e. with power applied).
•  It is measured in series with the circuit or component under test.
• Select highest current setting and work your way down.
• If you want measurement equivalent or more than 10A, change one of the probes to the last hole on the multimeter.

Precautions

• Always set the multimeter to the appropriate measurement you want to measure to avoid damage to it. Example measuring for ACV when the multimeter is being set to measure DCV.
• Whenever you see “OL” when taking a measurement, this means “Overload”. That indicates that the voltage or current is higher than the selected scale. You will need to change the range to get the appropriate measurement. This is quite different for a analog multimeter, when there is an overload the needle will swing across the scale and hit the “end stop”.
• The most important point to remember is when using multimeter  You must select a voltage or current range that is bigger or HIGHER than the maximum expected value, so the needle does not swing across  the scale and hit the “end stop.” If you are using a DMM  (Digital Multi Meter), the meter will indicate if the voltage or current is higher than the selected scale, by showing “OL” – this means “Overload.” If you are measuring resistance such as 1M on the  x10 range the  “OL” means “Open Loop” and you will need to change the range.  Some meters show “1′  on the display when the measurement is higher than the display will  indicate and some flash a set of digits to show over-voltage or over-current.  A “-1” indicates the leads  should  be reversed for a “positive reading.” If it is an AUTO RANGING meter, it will  automatically produce a reading, otherwise the selector switch must be changed to another range.