Technical data

5-47
Operating Concepts
Limit Line Operation
Limit Line Operation
This menu can be accessed by pressing LIMIT MENU, LIMIT LINE, within the system menu. You can have
limit lines drawn on the display to represent upper and lower limits or device specifications with which to
compare the test device. Limits are defined in segments, where each segment is a portion of the stimulus
span. Each limit segment has an upper and a lower starting limit value. Three types of segments are
available: flat line, sloping line, and single point. Limits can be defined independently for the four channels,
up to 22 segments for each channel. These can be in any combination of the three limit types.
Limit testing compares the measured data with the defined limits, and provides pass or fail information for
each measured data point. An out-of-limit test condition is indicated in five ways: with a FAIL message on
the screen, with a beep, by changing the color of the failing portions of a trace, with an asterisk in tabular
listings of data, and with a bit in the GPIB event status register B. (The analyzer also has a BNC rear panel
output that includes this status, but is only valid for a single channel measurement.) The limit test output
has three selectable modes.
Limit lines and limit testing can be used simultaneously or independently. If limit lines are on and limit
testing is off, the limit lines are shown on the display for visual comparison and adjustment of the
measurement trace. However, no pass/fail information is provided. If limit testing is on and limit lines are
off, the specified limits are still valid and the pass/fail status is indicated even though the limit lines are not
shown on the display.
Limits are entered in tabular form. Limit lines and limit testing can be either on or off while limits are
defined. As new limits are entered, the tabular columns on the display are updated, and the limit lines (if
on) are modified to the new definitions. The complete limit set can be offset in either stimulus or amplitude
value.
Limits are checked only at the actual measured data points. It is possible for a device to be out of
specification without a limit test failure indication if the point density is insufficient. Be sure to specify a
high enough number of measurement points in the stimulus menu.
Limit lines are displayed only on Cartesian formats. In polar and Smith chart formats, limit testing of one
value is available: the value tested depends on the marker mode and is the magnitude or the first value in a
complex pair. The message NO LIMIT LINES DISPLAYED is shown on the display in polar and Smith chart
formats.
The list values feature in the copy menu provides tabular listings to the display or a printer for every
measured stimulus value. These include limit line or limit test information if these functions are activated.
If limit testing is on, an asterisk is listed next to any measured value that is out of limits. If limit lines are on,
and other listed data allows sufficient space, the upper limit and lower limit are listed, together with the
margin by which the device data passes or fails the nearest limit.
If limit lines are on, they are plotted with the data on a plot. If limit testing is on, the PASS or FAIL message
is plotted, and the failing portions of the trace that are a different color on the display are also a different
color on the plot. If limits are specified, they are saved in memory with an instrument state.
Edit Limits Menu
This menu allows you to specify limits for limit lines or limit testing, and presents a table of limit values on
the display. Limits are defined in segments. Each segment is a portion of the stimulus span. Up to 22 limit
segments can be specified for each channel. The limit segments do not have to be entered in any particular
order: the analyzer automatically sorts them and lists them on the display in increasing order of start
stimulus value.