Hameg HM8115 Handbuch Seite 19

(6) INPUT 1 / OUTPUT 1 – INPUT 2 / OUTPUT 2
selector switch.
The POWER METER contains two measuring circuits
which are independent from each other. The active meas-
uring circuit is selected by "INPUT 1 / OUTPUT 1 – IN-
PUT 2 / OUTPUT 2" switch (6), which is located at the
rear.
If the selector switch (6) is in "INPUT 1 / OUTPUT 1"
position, the four banana jacks (15) at the front (INPUT 1
and OUTPUT 1) are active. INPUT 2 at the rear and OUT-
PUT 2 at the front are active when the selector switch
(6) is set to "INPUT 2 / OUTPUT 2".
(7) MONITOR (BNC socket) output.
The signal at this output enables the display of instanta-
neous power in combination with an oscilloscope, if the
WATT (12) or cos j (14) FUNCTION has been chosen.
The signal can not be evaluated in condition Var (13).
As the BNC socket is galvanically connected to chassis
and case, the reference potential at the BNC socket is
ground (PE). There is no galvanic connection to the meas-
uring circuits and the RS-232 serial port.
The signal polarity is inverted. A positive volt x current
product is displayed on the oscilloscope screen below
the zero volt trace position. It is recommended to use
the invert function of the oscilloscope to avoid misinter-
pretation.
The measuring circuit temperature drift is automatically
compensated on condition that WATT (12) is selected.
How frequently the compensation is performed, depends
on the temperature condition. During a compensation
period (approx. 100 ms) the output is switched to zero
Volt. The power signal is available without interruptions
if cos j (14) is chosen, as the temperature drift compen-
sation is switched off.
The following description applies to a signal display on
an oscilloscope with the invert function of the oscillo-
scope activated and explains the way to interpret the
power signal.
It must be noted, that the output signal is 2 Vrms at full
scale on each WATT measuring range. As the active
WATT range is not indicated by the POWER METER, it
must be calculated by multiplying the indicated VOLT
and AMPERE ranges.
Example:
The measurement shall take place when the 500 VOLT
range and 1.6 AMPERE range are selected, which means
that the actual power range is 800 Watt. Corresponding
to the specifications a voltage of 2 Vrms would be present
at the MONITOR output, if the load would have a power
consumption of 800 Watt.
An undistorted sinusoidal voltage of 230 V (50 Hz) shall
be applied at the measuring circuit input. The load shall
be purely ohmic, so that a phase shift between voltage
and current does not exist.
Änderungen vorbehalten / Subject to change without notice
Under these conditions the oscilloscope displays the
power consumption in form of an undistorted sinusoidal
voltage. The negative peak value will correspond with
the zero Volt trace position of the oscilloscope and the
positive peak value shall be 0.3 Volt. So the mean volt-
age at the MONITOR output is 0.15 V. As the 800 Watt
range is active in this example and full scale (800 Watt)
means 2 Vrms at the output, the power consumption
causing 0.15 V at the output can calculated with the equa-
tion:
800 x 0.15
X = ———————
2
The mean power consumption is 60 Watt.
Note:
Although the frequency of the AC voltage applied at the
measuring circuit input is 50 Hz, the oscilloscope dis-
plays the power consumption with a frequency of 100
Hz.
During one complete cycle of a 50Hz sine wave period,
there are two points where the power peaks, once dur-
ing the positive half cycle and once during the negative
half cycle. As these two (positive) peaks occur within
one input cycle, the frequency is doubled to 100Hz and
there are thus two points of zero crossover where the
MONITOR output is 0 Volt.
(8) (9) VOLT (pushbuttons) for manual or automatic VOLT
measurement range setting and associated LEDs. Both
pushbuttons react to step by step pressing.
After the POWER METER is switched on, the AUTO
LED is lit. Depending on the measuring circuit input volt-
age, the instrument automatically selects the suited
measurement range and displays it on the range LED. If
the input voltage changes in such a way that the previ-
ously selected range is no longer suited, the measure-
ment range will be changed automatically.
Pressing a VOLT (8) (9) pushbutton switches the auto-
matic ranging unit off and the AUTO LED is no longer lit.
Thereafter the measurement range can be selected by
one of the VOLT (8) (9) pushbuttons. The automatic rang-
ing unit can be activated again by pressing the right hand
VOLT (9) pushbutton until the AUTO LED is lit.
The VOLT display (2) indicates either the voltage applied
at the active measuring circuit or overflow if a too low
measurement range had been selected manually.
(10) (11) AMPERE (pushbuttons) for manual or automatic
AMPERE measurement range setting and associated
LEDs. Both pushbuttons react to step by step pressing.
After the POWER METER is switched on, the AUTO
LED is lit. Depending on the current value within the
measuring circuit, the instrument automatically selects
the suited measurement range and displays it on the
range LED. If the current flow changes in such a way
that the previously selected range is no longer suited,
the measurement range will be changed automatically.
Controls and Displays
19