3 - 44 USING THE COMBISCOPE INSTRUMENTS
3.8.4 Autoranging time base
The AUTO RANGE function of the Main Time Base (MTB) adjusts the time base
automatically, so that two to six waveform periods are displayed on the screen. If
a waveform doesn't contain enough information to calculate its period, the time
base is adjusted to acquire a minimum of two periods. One period of a signal is
determined by three successive crossings of the hysteresis band with the input
signal. The level of the hysteresis band can be set using the TRIGger:LEVel
command.
LIMITATION:
When operating with an acquisition length of 512 points, the maximum input
frequency is 25 MHz. For all other acquisition lengths, the maximum input
frequency is 50 MHz. When the input frequency is greater than the maximum alias
detection frequency, it is no longer possible to detect aliasing.
PROGRAM EXAMPLE:
CALL Send(0, 8, "INITiate:CONTinuous ON", 1) ’
CALL Send(0, 8, "TRIGger:SOURce INTernal1", 1) ’
CALL Send(0, 8, "SENSe:SWEep:TIME:AUTO ON", 1) ’
Figure 3.16 Definition of a signal period
PERI
D LEN
THPERI
D LEN
TH
ST7430
HYSTERESIS
TRIGGER
LEVEL
X2
X3X1
