Recording, Learning and Storing Facilities 1250 Frequency Response Analyzer
12-14 SH/1250/3
12.4 X-Y PLOTTER
12.4.1 INTRODUCTION
The results of measurements made by the 1250 can be plotted to provide a permanent
record. Any of the accepted formats (Bode, Nyquist, co-quad) is easily set up using the
front panel menus or by computer control. Axes and scales can be specified to give
precisely the plot that is needed; plot size is adjustable to suit pre-printed chart paper;
grid lines and axis legends are optional.
Suitable digital plotters can be driven by the 1250 without additional modules.
If an analog plotter is to be used, however, the 1250 must include the optional Plotter
Interface (12503). The use of analog plotters is described in Chapter 15 "Options".
The 1250 drives a digital plotter directly on the GPIB. To do this the GPIB plotter must
be switched to Listen Only mode (or addressed to Listen by using a suitable Controller),
and the 1250 must be switched to TALK ONLY using the switch on the rear panel (or be
addressed to Talk by using a suitable Controller).
The GPIB plotter section of the 1250 is compatible only with plotters using Hewlett-
Packard Graphics Language (HPGL), for example the HP 7470 Digital Plotter, or
Enertec Schumberger Graphics Language (ESGL), for example the Enertec 8500 TNP
Digital Plotter.
It could be convenient to put the 1250 results into its history file from which the data is
read for plotting. This permits a sequence of measurements to be run at maximum
speed, uninterrupted by the Controller needing to service other devices which may be
on the bus. The history file may also be used to view the results in order to decide the
best scales for the axes.
Another way of seeing graphical results is to pass the data to a computer from which a
VDU can display a plot. By this means the effect of adjustments to the system (of phase
margin, for example) can be observed, prior to obtaining a hard copy graph.
12.4.2 SETTING UP A PLOT: NON-PLOTTER MENUS
Set up the required Generator, Analyzer, Sweep (etc.) menus. It is convenient to enable
all functions except the Generator, which then acts as the 'on' switch when the plot is
ready to be performed.
Note: Ensure that the GPIB section of the DATA OUTPUT menu is switched 'off' (the
default state) so that only plotter commands will be passed to the GPIB.
As an example, the following settings produce a plot showing the amplitude of the first
16 harmonics of the square wave generated by the 1250 (Fig. 12.2). For this
measurement no external unit is required; connect the Generator output terminals on the
front panel directly to the Channel 1 terminals.
Set the Generator frequency to 1Hz, square wave, 10V amplitude, and switch 'off'.
Press the Analyzer RECYCLE key.
Enable the Sweep function by pressing START/CONTINUE followed by the HARMONIC
soft key.
All the remaining menus are left at their default states for this example plot, unless
otherwise indicated below.
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