ZES ZIMMER LMG450, User Manual

Page: 79 / 306

Z E S ZIMMER Electronic Systems GmbH Chapter 5
79
Signl Here you define the signal you want to trigger on. Available are: u, i, p, u², i²,
u
filt
, i
filt
, p
filt
. For the meaning of this values please watch the functional
diagram in 14.5, ‘Functional block diagram computing unit’
Filt Here you can define a digital filter which influences the signal to be triggered
on. Please note 2 points:
1. For Example: You have a 50Hz signal and select p, you have a 100Hz
p-wave! So a 87.5Hz filter will influence this trigger signal!!!
2. You should always try to switch the hf rejection filter on (see point
Filter/S-Cpl, Filt below) to prevent distortions on the trigger signal.
Especially when using frequency converters this hf rejection filter should
be switched on.
Level Here you select the trigger level. If you for example select ‘u’ and a level of
100.0 the instrument will be triggered each time the voltage crosses the
100V line. Please note: If you select u² the level is 100V² and you trigger if
|u|>10V!!
Hyst Usually you have a small noise on the signal. Without a hysteresis you might
get several level crossings at a single ‘real’ crossing. With the hysteresis you
can prevent this. For example you have a Level of 100V and a Hyst of 5V.
If your signal comes from a value smaller than 95V it has to climb up to
105V to get a positive crossing. If it comes from a value greater than 105V it
has to fall below 95V to get a negative crossing.
back returns to the last menu.
What can you do with this very special trigger mode?
If you have signals with a big DC part and a quiet small AC part (e.g. pulsed loads
with DC supply) you have the problem to trigger on the frequency of the AC part.
The solution is, to set the Level to a value of about the DC part, so you get a good
trigger level.
Another example is to measure pulse controlled currents. In fact this signals are AM
signals with a 50Hz carrier and for example a 1.5Hz modulator. To get correct
measuring results you would have to trigger on the 1.5Hz signal. To do this you just
select ‘i*i’ as source and a 30Hz filter. So you have built up a quadratur demodulator.
Now you select a trigger level (depending on the current) and your instrument will
synchronise to the 1.5Hz signal of your pulse control.
Filt Here you can switch on/off the filters in the measuring signal path of voltage and
current. This filters are only in the signal way (they influence the sampling values) and
don’t influence the synchronisation settings ‘U’ and ‘I’. But they influence the
synchronisation Xtrig because it is using the sampling values! Possible settings are: