Average Power; Frequency; Function; Isolated - Hameg Instruments HM8115-2 Manual Del Usuario

O p e r a t i n g c o n t r o l s a n d d i s p l a y s
Power factor (PF)
In this mode the power factor will be measured, the LED will

light up, the display will show the power factor = active/ by
apparent power. The HM8115-2 allows the measurement of
the average of the instantaneous power irrespective of the
waveform as long as the specifications for crest factor and
frequency are observed.
Please note that a power factor can only be shown for
AC or AC + DC signals of sufficient minimum amplitu-
des. If the signal amplitude of either voltage or current
or both is insufficient horizontal bars will be displayed,
this will also be the case if DC is being measured.
STOP
ϕ
cos is only defined for truly sinusoidal signals. As
soon as at least one of the signals is distorted a cos
derived from the phase shift between voltage and
current will not be identical to the true power factor.
HINT
Connectors

MONITOR (BNC)
This is an analog output representing
the instantaneous active power e.g.
for display on a scope.
The instantaneous power
is the product of voltage and
current at time (t)
HINT
p(t) = i(t) · u(t)
in case of sine wave:
ϕ)
· î sin ωt
p(t) = û sin (ωt +
The active power is the average of the instantaneous power
integrated over the interval T = period divided by the period T:
T
∫
1
î sin ωt · û sin (ωt + ϕ) dt
P = ––
T
0
î · û · cos ϕ
P = ––––––––––––––
2
· cos ϕ
P = V · I
rms rms
The monitor output will always deliver the instantaneous po-
wer no matter which function was selected. For positive
instantaneous power the output will be positive, for negative
instantaneous power it will be negative. If DC is being
measured the monitor output will hence deliver a DC signal.
The BNC terminal outer conductor is connected to the
instrument housing, however, the signal is isolated by a
transformer.
The temperature dependent drift is automatically corrected
for by disconnecting the input/output terminals, during this
interval (100 ms) there will thus be no monitor signal. After
instrument turn-on the autozero will be activated every 3
seconds for the first minute, after warm-up the breaks will
occur every 2 minutes.
The average of the monitor output voltage will be 1 V
if the input signals are such that the WATT display
shows full scale. There is no indication of the power
range, the range has to be calculated and is the
product of the VOLT and AMPERE ranges.
STOP
34
Subject to change without notice
ϕ
1
5
Examples: Examples: Examples: Examples: Examples:
50 V x 0,16 A = 2408 W
150 V x 16,0 A = 2400 W
500 V x 1,6 A = 800 W
If both voltage and current are equal to their full
scale values in the ranges selected and if both are
sinusoidal the monitor output signal will be 2 V
the power is purely active the signal will oscillate
between 0 and 2 V , the average of this is 1 V.
p
For DC full scale values the monitor output will be
1 V .
DC
HINT
Example 1:
A wirewound resistor of 1.47 K is connected to 70 V
picture shows the voltage across the resistor and the monitor
output. The ranges selected are 150 V and 0.16 A which yields
a 24 W full scale 1 V average signal at this output. There is no
phase shift.
Ω
R : 1,47 k
L
The scope shows an undistorted instantaneous power signal.
The negative peak is equal to 0 V, the positive peak equals
0.27 V, thus the average equals 0.135 V.
This average value multiplied by the full scale value 24 W
equals 3.24 W which is the average power.
The HM8115-2 displays the following results:
V = 70 V
rms
I = 0,048 A
rms
P = 3,34 W
Example 2:
A wirewound resistor of 311 ohms is connected to 50 Vrms/50
Hz. The picture shows the voltage across the resistor and the
monitor output.
The ranges are 50 V and 0.16 A, the full scale power is hence
8 W corresponding to 1 V average at the monitor output.
There is no phase shift with this purely resistive load. The scope
shows an undistorted signal. The negative peak equals 0 V,
the positive peak 2 V, the average is thus 1 V.
1 V (average)
1 V (average)
1 V (average)
. If
pp
. The
rms
Voltage
at R
L
100 V
50 V
GND
Monitor
Signal
100 Vm
GND
Q = 0,2 var
S = 3,32 VA
PF = 1,00