Fluke 281 User Manual page 250

291, 292, 294
Users Manual
on a single channel instrument, or
on a multi-channel instrument. It is then possible to select the source to be either an
external signal on the ARB CLOCK IN/OUT socket or the internal system clock; see the
Reference Clock IN/OUT and System Clock Setting sections of Chapter 15, System
Operations from the Utility Menu for the use of and frequency setting for the system
clock.
Note that SEQUENCE and the 'standard' waveforms of square, pulse and pulse-train
also operate in clock synthesis mode and consequently can also be set to external clock
on the appropriate FREQUENCY menus; refer to the relevant sections for further details.
Having selected external clock the arbitrary waveform will continue to run from the
internal clock until the instrument receives the first rising edge of the external clock; at
that point the hardware switches over to the external source.
The following applies only to internal clock selection.
Frequency can be set in terms of frequency or period, as for standard waveforms, by
pressing the freq or period soft key respectively. Additionally, for arbitrary
waveforms, frequency or period can be set in terms of the sample clock frequency, by
pressing the sample soft key, or in terms of the waveform frequency, by pressing the
waveform soft key. The relationship between them is:
Frequency and period entries are made directly from the keyboard or by using the rotary
control in the usual way. Pressing the FREQuency key with sequence running calls the
SEQ FREQUENCY screen:
With internal clock selected (the default), frequency or period can now only be set in
terms of the clock frequency. Frequency or period entries are made directly from the
keyboard or by using the rotary control in the usual way.
With external clock selected using the SEQ FREQUENCY soft key the sequence can
be clocked using an external source connected to the rear panel ARB CLOCK IN/OUT
socket.
9-14
ARB FREQUENCY: ext
source: ext arb clk
freq: 10.0000000kHz
waveform frequency = sample frequency ÷ waveform size.
SEQ FREQUENCY: int
100·00
freq
MHz
period