Fluke PM3370B user manual Vertical Coupling AC, DC, GND, 14HOW to USE the Instrument

4 - 14HOW TO USE THE INSTRUMENT

VERTICAL COUPLING AC, DC, GND

The input coupling after AUTOSET is ac. Since the Probe Adjust signal is a pulse type signal with a 50% duty cycle, its mean value is at the signal’s 50% amplitude level. When the input is ac coupled, the mean value will be displayed at the ground level of the oscilloscope. As a result of this, the displayed waveform is centered on the screen.

AC coupling can be used to examine small ac components that are superimposed on large dc voltages.

-Press the AC DC GND key once for DC input coupling.

Since the Probe Adjust signal is a pulse-type signal with a lower level of 0V, and a higher level of 600 mV, and since the oscilloscope adjusts the display position of the ground level to coincide with the screen center, switching from ac coupling to dc coupling results in an upward shift of the display position of the signal.

The coupling sign in the lower left hand corner of the screen changes from ∼ (ac) to = (dc).

The ground level for each of the channels is indicated by a dash after the channel identifier, i.e., ’1-’ for the ground level of channel 1.

0.5ms

600mV

0V

Input Signal

AUTO SET	AC DC		AC DC
	GND		GND
			1-
1-	1-
AC DC
GND
CH1 200mV	CH1	200mV	CH1 200mV
AC Coupled		DC Coupled	GND Coupled
			ST6708

-Press the AC DC GND key to obtain ground coupling.

A straight line is now displayed. This is the 0V (ground) level of the input. This level serves as the 0 volt reference for amplitude measurements.

The coupling sign ’⊥’ now indicates ground coupling.