WATTMETERS
Test Instruments & Measuring Devices
WATTMETERS
Wattmeters are used to determine DC power or real AC power delivered to the
load.
EO 1.2
STATE the electrical parameters measured by each of
the following in-place measuring devices:
d.
Wattmeter
EO 1.3
EXPLAIN how the following electrical test equipment
and measuring devices are connected to a circuit:
d.
Wattmeter
Wattmeter
The wattmeter is an instrument
Figure 11 Wattmeter Schematic
which measures DC power or true
AC power. The wattmeter uses
fixed coils to indicate current,
while the movable coil indicates
voltage (Figure 11). Coils LI1 and
LI2 are the fixed coils in series
with one another and serve as an
ammeter. The two I terminals are
connected in series with the load.
The movable coil Lv, and its
multiplier resistor Rs, are used as a
voltmeter, with the V terminals
connected in parallel with the load.
The
meter
deflection
is
proportional to the VI, which is
power.
Wattmeters are rated in terms of
their maximum current, voltage, and power. All of these ratings must be observed to prevent
damage to the meter.
Equation (14-15) is the mathematical representation of calculating power in a DC circuit.
(14-15)
P
VI or P
I2R
ES-14
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