Lake Shore Model 480 Fluxmeter User’s Manual
5-14
Advanced Operation
5.11 PEAK HOLD AND PEAK RESET
The Model 480 has high speed peak hold hardware that can be used to capture positive and negative
peak values. Software stores the measured peaks to prevent any sag in the hold circuits from changing
the display value. Peak hold operation can be used during DC or AC operation.
5.11.1 Peak Hold in DC Mode
The peak hold feature has very little effect on DC mode operation. The peak hold circuit captures and
holds the highest and lowest value present in the DC signal path since the last peak reset. The circuit
is many times faster than the instrument update rate and can capture an hold signals that cannot
otherwise be seen on the display. The peak hold circuit was designed to keep up with the fastest
magnetizing pulses.
Drift is as much a problem in DC Peak mode as DC mode. Drift compensation and integrator resets
are necessary when making DC Peak measurements. DriftTrak does not attempt to correct drift
during DC Peak operation.
5.11.2 Peak Hold in AC Mode
During AC mode operation the peak hold feature bypasses the RMS converter. The peak amplitude
of a periodic wave form is believed to be more useful than the maximum RMS value. The highest and
lowest “peak” AC values (not RMS values) present in the AC signal path are captured and held. This
distinction can cause some confusion. For a sinusoidal wave form the peak value is approximately
1.4 times higher than the RMS. For non-sinusoidal wave forms the difference can be much larger.
AC Peak mode uses the same fast peak hold circuit as DC Peak mode enabling operation over a
wide frequency range for periodic signals. No drift compensation is required for AC Peak operation.
Non-periodic field changes can also be captured using AC Peak mode. There are several possible
applications, including magnetizers, for a drift free integrator with several gain ranges and a high
speed peak hold.
5.11.3 Activating Peak Mode
To turn peak mode On or Off, press the
Peak Hold
key. The screens below illustrate positive peak,
negative peak, and both peaks.
^+2.9758kGDC
«-1.8736kGDC
^+2.9758kGDC
«-1.8736kG
NOTE
: The up caret (
^
) or down caret (
«
) next to the peak reading indicates positive or negative
peak operation, respectively.