Electric Meters

1
Electric Meters

• Electricity for Refrigeration, Heating and Air
  Conditioning 7th Edition

Chapter 4 Electric Meters
2
Electric Meters

• Upon completion of this chapter the student will
  be able to

• Describe the use of the volt-ohm meter and
  clamp-on ammeter in the heating , cooling, and
  refrigeration industry.
• Explain the operation of the basic electric
  analog meter
• Explain how analog electric meters transfer a
  known value in an electrical circuit to the meter
  movement.
• Describe the operation of an analog voltmeter.
• Describe the operation of an analog and digital
  clamp-on ammeter.
• Describe the operation of an analog ohmmeter
• Explain the operation of a digital volt-ohm
  meter.
• Give the advantages and disadvantages of the
  analog and digital meters.
• Describe the conditions of resistance that can
  exist in an electrical circuit in reference to
  continuity.
• Describe the source of energy for the operation
  of the analog voltmeter, ammeter, and ohmmeter.

3
Key Terms

• Ammeter
• Analog Meter
• Clamp-on Meter
• Continuity
• Digital Meter
• Magnetic Field
• Measurable Resistance
• Ohmmeter
• Open
• Short
• Voltmeter

4
Introduction

• The most common characteristics in a circuit that
  are most important to industry technicians are
• Volts
• Amperes
• Ohms
• The most popular electrical meters are built
  around these three electrical characteristics.
• Most meters are capable of reading more than one
  electrical characteristic.
• The most common electrical meters used are the
  volt-ohm-milliammeter and the clamp-on ammeter.

5
Electric Meters

• An electric meter is a device used to measure
  some electrical characteristic of a circuit.
• The most common types of electric meters are the
  voltmeter, the ammeter and the ohmmeter.
• Warning Use the proper Electrical test
  equipment for the job being preformed

6
Basic Principle

• Most electric measuring instruments make use of
  the magnetic effect of electric current.
• When electrons flow through a conductor in an
  electric circuit, a magnetic field is created
  around the conductor.
• The magnetic field is used to move the needle of
  a meter a certain distance, which represents the
  amount of the characteristic being measured.

7
Differences Among Meters

• The differences among the various electric meters
  are not in the meter movements, except for
  digital meters, but in the internal circuits of
  the meter and in how the magnetic fields are
  created.

8
Clamp-on Ammeter

• The clamp-on meter picks up the magnetic field
  through a set of laminated jaws on the meter.

9
The Voltmeter

• The voltmeter uses a resistor as a load to
  produce a magnetic field when voltage is applied
  to the circuit in the meter.

10
The Ohmmeter

• The ohmmeter has its own power supply and uses
  the device being checked as the load to produce a
  magnetic field.

11
Ammeters

• The strength of the magnetic field determines the
  distance that the needle of the meter moves.
• The larger the current flow, the stronger the
  magnetic field grows and the greater the needle
  movement on the scale.
• The ammeter measures current flow in an electric
  circuit.
• There are two types of ammeters used in the
  industry today the clamp-on ammeter and the
  in-line ammeter.
• The clamp-on ammeter is the most popular and the
  easiest to use.

12
Using the Ammeter

• Select the scale that is appropriate for reading
  the current draw of the electrical device being
  checked.
• If the appropriate current is unknown, use the
  highest scale until the correct scale can be
  determined.
• Clamp the jaws of the ammeter around one
  conductor supplying a load or circuit.
• Never clamp the jaws of the meter around two
  wires to obtain an ampere reading.
• If the current flows in the wires are opposite,
  the meter will read zero because the current
  flows cancel each other out.
• If the current flow are not opposite, the meter
  will read the current draw in both conductors.

13
Using the Ammeter

• When the ampere draw is small, you may have
  difficultly obtaining a true reading because of
  the small needle movement.
• This can be remedied by coiling the wire around
  the jaws of the meter. This allows the meter to
  pick up a larger current flow than is actually
  there.
• To obtain the correct ampere reading when this
  method is used, divide the ampere draw read by
  the number of loops going through the jaws of the
  meter.

14
Voltmeters

• The voltmeter is used to measure the amount of
  electromotive force available to a circuit or
  load.
• Most voltmeters can read both voltage and
  resistance.
• The most common volt-ohm meter has three voltage
  scales and several voltage ranges.
• All equipment is designed to operate at a voltage
  of 10 above or below the rating of the
  equipment.

15
Ohmmeters

• The ohmmeter is used to determine the operating
  condition of a component or a circuit.
• The ohmmeter can be used to find an open circuit,
  an open component, or a direct short in a circuit
  or component.
• Continuity is when a particular circuit or
  component has a complete path for current to
  follow.
• The term measurable resistance is the actual
  resistance that is measured with the ohmmeter.
• The ohmmeter provides an easy method for checking
  circuits for opens and shorts and for measuring
  resistance.