Ametek 7270 Instruction Manual page 104

Chapter 5, FRONT PANEL OPERATION
5-56
This menu has six controls affecting the virtual reference mode, a single display, and
two keys to establish virtual lock. The left-hand side of the display is used for the
semi-automatic method of establishing Virtual Reference mode, with the right-hand
side being used for the manual mode.
The controls operate as follows:-
Semi-Automatic Method
START FREQUENCY
This control defines the start frequency from which the instrument will begin to try
to find the applied signal. It should be set to a value close to, but less than, the
expected signal frequency. If the start frequency is within 100 Hz of the signal
frequency then there is no need to set the stop frequency control. Adjusting the Start
Frequency control also sets the present Oscillator Frequency to the same value.
STOP FREQUENCY
This control defines the stop frequency at which the instrument abandons its search
for the signal, and should be set to a value greater than the expected signal
frequency. If the start frequency is within 100 Hz of the signal frequency then there
is no need to set this control.
STEP SIZE
This control defines the frequency step size used during the automatic search. Note
that it should only be adjusted after a search has begun if it is taking a long time to
find the signal.
TIME/STEP
This control defines the time per point within the automatic search. Note that it
should only be adjusted after a search has begun if it is taking a long time to find the
signal.
START AUTO SEARCH
Pressing the Start Auto Search key starts the internal oscillator at the defined start
frequency and increases it at a rate of 1 Hz per second. If the instrument detects a
signal greater than 50% of full-scale then the search stops, the unit locks on to that
signal, and the Main Display - Virtual Reference Mode appears, as shown in
Figure 5-43, Virtual Reference Menu