Transcript Islide13-Metering

Chelmsford Amateur Radio Society
Intermediate Course
(3) Using Multimeters
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
1
Multimeter Purpose
• Used to measure Voltage and Current around a circuit.
• Multimeter is the generic name given to the universal,
Volt, Amp, and Ohmmeter.
• There are several on the market and can be either
Analogue or Digital in operation.
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
2
Operational Considerations
• Take care to set the meter to appropriate range before
connecting to the circuit.
• Set to highest range and work down, to protect the meter.
• There may be a need to switch off equipment before
connecting to High Voltages.
• ALWAYS HAVE ONE HAND IN THE POCKET OR BEHIND
BACK, AND REMOVE RINGS IF WORKING ON HIGH
VOLTAGES.
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
3
Meter Polarity
• There are many cases for observing the correct polarity
when making measurements.
• When taking measurements of Volts or Amps always
check the probes are connected to the correct terminals.
• This is easy if the probes have RED+ and BLACK- leads,
but meters purchased from rallies or privately may just
have leads of same colour.
• NB On Resistance ranges Analogue meters may put out
opposite polarity!
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
4
Analogue vs Digital
• Digital meters normally have high input impedance.
• Accuracy of analogue meters are specified in Ohms per Volt.
• Digital meters are simple to read - the display is normally clear.
• Analogue meters are good when making adjustments, when you are
looking for a change in values.
• The reading of an Analogue scale can be harder.
• Analogue meters will draw some current from the circuit being
measured, therefore care is required when interpreting the results.
• Digital meters auto-sense polarity. Be careful with Analogue ones
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
5
Measurements
• To measure a Voltage or Potential Difference a Voltmeter is
connected in parallel with the circuit.
• To measure current the Ammeter is connected in series with
the circuit to be measured.
-
A
+
+
Bulb
Battery
+
V
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
6
Analogue Diode Testing
• Analogue meter on
Resistance Range
• Diodes are sensitive to
internal battery polarity
• Some Digital meters
have dedicated
functions for this with
‘normal’ polarity
+
Internal
Battery
+ RED LEAD
Meter
Display
Meter
- BLACK LEAD
LOW READING
HIGH READING
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
7
Measure Potential Difference
+ 6 / 9 Volts
120K
56K
47K
180K
- Volts
Measure the Potential Difference across each Resistor and
record the result for Digital and Analogue Meters
Chelmsford Amateur Radio Society
Intermediate Licence Course
Carl G3PEM
Slide Set-13
(3) Using Multimeters
8