Voltmeters, Ammeters, Ohm
2
Meters
n
Analog meters
n
n
n
n
Use some sort of electromechanical mechan
cause a small arm to move.
Provides a continuously varying readout with
discrete jumps.
Tracks changes in meter readings.
Digital meters
n
n
n
2006/9/15
The meter reading is converted into decimal
Different people viewing the same meter wil
the same reading.
Not to assume that the presence of many di
digits means very high accuracy.
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
3
DC voltmeters
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
4
AC voltmeter
n
n
n
n
Average responding meter
Peak-reading meter
True-RMS meter
Coupling
n
AC coupled
n
n
n
Include a coupling capacitor on the input of voltm
Block DC voltage
DC coupled
2
2
VRMS = VDC
+ VAC
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
5
RF probe
n
Radio frequency probe is often used to e
DC voltmeter to make high frequency AC
measurements.
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
6
Ammeters
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
7
Ammeter used as voltmeter
I=
n
n
n
2006/9/15
V
R
Rs is usually chosen to be fairly large
Rs is limited by the sensitivity of the ammete
The larger the Rs, the littler the current
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
8
Voltmeter used as Ammeter
I = I M RP
n
n
2006/9/15
Make Rp as small as possible
The smaller the Rp, the littler the voltage
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
9
Ohmmeters
n
Voltmeter-Ammeter method
n
Current-Source method
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
10
Ohmmeters
n
4-wire Ohms measurement
n
n
Current source will maintain a constant curre
No current flowing through two leads
Voltage error
Hig
2006/9/15
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
11
Other multimeter function
n
Continuity indictor
n
n
Diode test
n
n
n
n
Display voltage drop across diode
Frequency counter
n
n
Tracing out wires in a circuit
Measures frequency of AC signal
Min., Max., average readout
Capacitance measurement
Temperature measurement
n
2006/9/15
Requires external temperature sensor probe
Dept. of Electronic Engineering, National Yunlin Univ. of Science and T
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