Rohde & Schwarz HM8118, User Manual

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55
Instrument Functions
setting is a compromise between measurement accu-
racy and measurement speed. A low measurement speed
(SLOW) implies a higher measurement accuracy, corre-
spondingly a high measurement speed (FAST) implies a
low measurement accuracy. For very low measurement
frequencies, the measurement speed is automatically
reduced.
7.1.6 Triggering TRIG
The trigger source and trigger operating mode can be se-
lected here. The following trigger operating modes and
trigger sources are available:
❙ CONT (continuous trigger):
A new measurement is automatically performed at the
end of a previous measurement.
❙ MAN (manual trigger):
A measurement is performed when the TRIG / UNIT key
27
is pressed. The activated manual trigger function will
be marked as TGM on the screen.
❙ EXT (external trigger):
A measurement is performed when a rising slope is
applied to the external trigger input (TTL level +5V).
During a measurement, all potential signals at the trigger
input will be ignored until the current measurement has
been fully completed. If a measurement is triggered, the
TRIG key
27
will be illuminated. The activated external trig-
ger function will be marked as TGE on the screen. A
single measurement will be performed for each tirggered
triggering.
7.1.7 DELAY Function
The DELAY function defines the trigger delay time. It can
be set anywhere between 0ms and 40000ms (40s). In the
SETUP menu, use the arrow keys
7
to select
the DELAY function to set the trigger delay time, press the
knob
6
(editing mode) and select the desired trigger de-
lay time via knob. By pressing the knob again, you can ac-
tivate the manual value input via numeric keypad. A va-
lue input window will be opened. You can use the numeric
keys to enter a value. After entering the value via keypad,
confirm the entry by pressing the ENTER key or by pres -
sing the knob again.
7.1.8 Average Value AVG
When the function AVG Average Value is activated, seve-
ral individual measurements will be used to form a mean
value according to the set period. To determine the num-
ber of measurement periods to form the mean value, in the
SETUP menu, use the arrow keys
7
to select the
AVG function, press the knob
6
(editing mode) and select
the desired average by mean. By pressing the knob again,
you can activate the manual value input via numeric key-
pad. A value input window will be opened. You can use
the numeric keys to enter a value. After entering the va-
If the measuring instrument shows a blank screen (i.e. lines "- -
-“) without measurement values, no trigger event / measurement
has been triggered or the selected measurement function has
been selected incorrectly.
lue via keypad, confirm the entry by pressing the ENTER
key or by pressing the knob again. The number of mea-
surement periods for the averaging measurement can be
set between 2 and 99 or to MED (medium). The MED (me-
dium) setting is the medium averaging mode. The bridge
R&S®HM8118 performs 6 consecutive measurements, re-
jects the lowest and highest measurement values and ge-
nerates an average based on the four remaining measure-
ments. This type of averaging hides individual erroneous
measurements. If the averaging function is activated, the
symbol „AVG“ will be shown in the display. The averaging
function can also be used for a manual or external trigge-
ring. However, the number of measurements per trigge-
red triggering will be determined by the set number of ave-
rages (periods).
For instance, if a component is integrated in a measure-
ment adapter, the first measurement generally is errone -
ous and differs greatly from all subsequent measurements.
Therefore, the first erroneous measurement is rejected to
prevent an erroneous display of measurement values by
measuring transient processes.
7.1.9 Display of Test Signal Level
V
m
(Measurement Voltage) / I
m
(Measurement
Current)
Use the function V
m
/I
m
to turn the display for the voltage
that is measured at the connected component as well as
the display of the measured current that flows through the
connected component on (ON) and off (OFF). In the SE-
TUP menu, use the arrow keys
7
to select the
V
m
/I
m
function, press the knob (editing mode) and activate
or deactivate the function via knob. Press the knob again
to confirm the selection.
7.1.10 Guarding GUARD
It the GUARD function is activated, the shield covers for
the BNC connectors
20
...
23
will be connected to an inter-
nal generator and supplied with a reproduction of the mea-
surement voltage. Within certain limits, this eliminates the
cable capacity which would otherwise result in erroneous
capacity measurements. The GUARD function is applied
for low voltages.
The following settings options are available:
❙
OFF (off) :
Guarding is not used; the shield cover for the BNC
connectors will be connected with ground potential.
❙
DRIVE (controlled):
The shield cover for the BNC connectors will be
connected to the LOW DRIVE potential via internal
generator.
❙
AUTO (automatic):
For frequencies below 100 kHz and for measurement
ranges 1 to 4, the external contacts of the BNC
connectors are connected with ground potential; for
frequencies above 100 kHz and measurement ranges 5 or
6, the external contacts of the BNC connectors are
connected with an active protective voltage source (for
the potential control).