3-13. DISPLAY OFFSET
The 4278A also has a display value offset function that adds or subtracts a constant value
to/from the measurement result. Offset A subtracts a pre-entered value from the capaci-
tance measurement result. Offset B subtracts a pre-entered value from one of the following
parameters 0, Q, G, and ESR (Rs). The pre-entered Offset B value is dependent on the
parameter. For example, assume that you have entered the offset B value when the Cp-D
parameter is selected and offset B is on. If the measurement parameter is changed to a
parameter other than Cp-D or Cs-D, the offset B function is automatically turned off, be-
cause the second parameter (D) does not match.
3-14. VALUE MONITOR
The 4278A has a value monitor function which can be used to monitor open capacitance
and conductance for open compensation, short inductance, and resistance for short com-
pensation, reference value (pre-measured) of a working standard, actual measurement value
of a working standard, display offset values, and nominal value for tolerance mode sorting.
When a compensation measurement is made, the monitor will be automatically turned on.
3-15. TRIGGER MODE
The 4278A has three trigger modes -- INTernal, EXTernal, and MANual.
INT TRIG:
The 4278A continuously repeats measurements except during special operations, e.g., edit-
ing the limit table.
MAN TRIG:
The 4278A performs a single measurement every time the TRIGGER key on the front panel
is pressed.
EXT TRIG:
The 4278A performs a single measurement every time a positive going TTL pulse is applied
to the EXT TRIGGER connector on the rear panel. External triggering can be also be
achieved by momentarily switching the center conductor of the EXT TRIGGER connector to
chassis ground (center conductor circuit contains a pull-up resistor) . Figure 3-15 shows
the required TTL pulse.
NOTE
The 4278A ignores triggers that are applied while a measurement is in progress.
Trigger the 4278A after the measurement is completed.
Select the EXT TRIG mode when the 4278A is triggered via an optional interface.
3-23
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