Using Auto Trigger Level; Using V Peak A; Using User Gate - Keithley 776 Instruction Manual

3. To remove the instrument from its one-shot arming
mode, turn the hold function off by pressing in sequence
the [2nd] and [HOLD] push-buttons.
3-15. Using Auto Trigger Level
The auto trigger level function is extremely useful when
measuring repetitive signals having an unknown dc
component. The auto trigger is capable of finding the
peaks of the signal and then setting the trigger level
exactly at their center. In addition. The auto trigger
automatically sets the correct attenuation and adjusts
the input signal to fit within the dynamic range. The auto
trigger mode does not operate on totalize B and fre-
quency C functions. Auto trigger level function works
independently in conjunction with Channels A and B.
To set the Model 776 to operate in auto trigger mode
proceed as follow:
1. Press in sequence the
[2nd]
and the
[AUTO
TRIG]
(second function to [TL A])push-buttons. Observe that
the AUTO TRIG light illuminates: indicating that the
auto trigger function is selected. When the indicator is
off. the instrument is in its normal manual trigger level
mode.
2. Apply the signal to be measured to the appropriate
input connector. After a short search sequence. the gate
opens and the measurement is processed.
3. TL A or TL B lights blink if an error was detected.
Refer to paragraph 3-6-3 for a additional error indica-
tions information.
4. To return the Model 776 to normal trigger level mode.
press in sequence the
[2nd]
and the [AUTO TRIG]
push-buttons.
3-16. Using V Peak A
The V PEAK A function turns the Model 776 into a
versatile RF peak voltage meter where both lou and
high peaks are detected. processed and displayed. This
is especially useful in analyzing both the amplitude and
the dc component of an unknown signal. Their are two
available measurement rates for the V Peak function:
Fast for normal measurements abol-e IO0 Hz. and slow
rate for measurements of signals belox\ 100 Hz. To
select the V Peak A function proceed as follows:
1. Press in sequence the [2nd] and the
[V PK A]
(second
function to [FREQ]) push-buttons. Obseme that the
VOLTS light illuminates. This indicates that the instru-
ment is now set to V Peak A measurements. The normal
display reading is transform into a two section display
like the following:
3-12
The three digits on the left indicate the lower peak
amplitude. The right three digits indicate the higher
peak amplitude. Negative values have a leading minus
sign where positive values have no sign. The minus sign
and the decimal points are automatically set by the
instrument.
0.00 0.00
2. To select the measurement rate press the
[CT]
push-
button in the DISPLAY/MODIFY group and obscrvc
that the reading on the display is as follows:
FASt
This reading indicates that the instrument is set to its
fast measuring rate.
Now
press the
[VERNIER fi]
push-
button once and obsene that the display reading is
changed to the following:
SLO
This reading indicates that the instrument is set to
measure the V Peak A with its slow measuring rate.
Press the [GT] push-button again. The instrument IS
now ready to perform the required function.
3. Press the [GT] push-button to return the counter to
normal V Peak display.
4. Press one of the FUNCTION push-buttons to select
another function. Observe that the display returns to
normal display reading and that the VOLTS light turns
off.
3-17. Using User Gate
The User Gate is useful when a gate time other than the
internal pre-determined gate times is rcquircd. The lim-
its which must be observed are the mininwtn limit of
100 yS and the maximum limit of IOOO s. The User Gate
function is accessible in FRQ A. B and C. FRQIB. PER
AVG. PLS AVG. and TI AVG A to B operating modes.
To operate the instrument in its User Gate mode proceed
as follows:
1. Set the instrument to PRQ A. Press the
[GT]
push-
button once. 0bsen:e that the Gate light turns on, and
that the instrtunent displays the gate time.
2. Press and hold the
[VERNIER
n] push-button and
obsense that the display increments. Afler the 100 s gate
time the instrument enters the User Gate mode and
displays the following readout:
USEr GAtE