# Electrical and Electronics eLearning

### NUE 052 - Units of Measurement and Meters

#### The four basic units of electrical measurement are Volts, Amps, Ohms and Watts.

• Volts is electrical pressure - the potential difference measured between 2 points in a circuit
• Amps is electrical current - the flow of current in a circuit from positive to negative
• Ohms is electrical resistance - the opposition to current flow in a circuit
• Watts is electrical power - the electrical energy in a circuit
• Click here to see Ohms law using Volts, Amps, Ohms and Watts
• #### To measure electrical units we need to use an instrument called a meter.

Meters come in all shapes and sizes, each for a different purpose. We can have special purpose meters that measure just one type of unit such as watts or an instrument called a multimeter which is capable of measuring volts, amps and ohms.
Even though the multimeter can measure three electrical units, the meter must be connected differently in the circuit.
• To measure Volts - connect the meter in parallel with the circuit under measurement while connected to the supply.
• To measure Amps - connect the meter in series with the circuit under measurement while connected to the supply.
• To measure Ohms - connect the meter in parallel with the circuit under measurement with the supply disconnected.
• #### Multiples and sub-multiples

Meters come in all shapes and sizes, each for a different purpose. We can have special purpose meters that measure just one type of unit such as watts or an instrument called a multimeter which is capable of measuring volts, amps and ohms.
• Electrical measurements can be from thousands of amps to millionths of an amp.
• Terms used for these measurements 'kilo' and 'milli' are called multiples and sub-multiples.
• A few examples are listed in the following table:
Term
Symbol
Multiplier
Example
mega
M
1,000,000
107MHz = 107,000,000 hertz
kilo
k
1000
5kV = 5000 volts
milli
m
0.001
6mA = 0.006 amps
micro
u
0.000001
2uA = 0.000002 amps

#### Conversion Examples:

Question: A resistance reading is 4.7 Megohms. How many ohms does this represent?
Answer: Mega is one million so multiply 4.7 by 1,000,000 by moving the decimal point six places to the right 4,700,000 ohms
Question: There is 2.45 mA flowing in a circuit. How many amps is this?
Answer: Milli is one thousand so divide 2.45 by 1,000 by moving the decimal point 3 places to the left 0.00245 amps

#### Scientific Notation

Scientific Notation is a way of expressing multipliers (see previous table) in mathematical form. Each multiplier is treated as a power of 10. Following are examples scientific notation using the examples from the previous table:
Term
Symbol
Multiplier
Example
Scientific Notation
mega
M
1,000,000
107MHz = 107,000,000 hertz
106
kilo
k
1000
5kV = 5000 volts
103
milli
m
0.001
6mA = 0.006 amps
10-3
micro
u
0.000001
2uA = 0.000002 amps
10-6

#### Conversion Examples:

Question: Convert 10kV to volts
 10kV = 10 x 103 V (k = 103) = 100 x 102 V (1 decimal place right) = 1000 x 101 V (2 decimal places right) = 10000 x 100 V (3 decimal places to right) 10kV = 10,000 V
Question: Convert 0.10mA to microamps (uA)