Control Selection - Keithley 776 Instruction Manual

FUNCTION ___~~~~~~DEFAULTSTATE~~.~~~~~_
Function Frequenn A
Display/Modify Normal reading
Gate/Delay Time I.0 s
Trigger Levels A & B 0.00 v
Coupling DC
Slope
Positive going
Attenuators off
Filters Off
impedance lMX2
Averaging Off
Auto Trigger
Off
Delay Off
Sampling Rate
Normal - 3 reading/s
Ratio Mode A/B
V Peak A Rate Fast
Totalize Mode Infinite
Displayed Digits
10
IEEE Status Local
Note: The Model 776 and 776/2,4G/R have a de-
fault gate time of I second. The Model
776/2.4G/R has a default gate time of IOOms.
Table 3-1.
Dejiiult Stntcs After Sojiivnre Reset
and enables remote operation. In this case. all front
panel push-buttons. except [LCLJ. are disabled. An
attempt to press one of these push-buttons will cause the
following message to be displayed:
PrESS LcL
This message indiiates that the inswument will ignore
any front panel programming scquencc unless the
[CLRlLCL] push-button is pressed and the REMOTE
light turns off.
3-6-2. Error Indication
There are several error indications that are caused bj
either an incorrect front panel programming or insuffi-
cient input level conditioning which is otherwise re-
quired by the instrument for normal signal processing,
These indications are either visible (blinking LED) or
audible (beeper) and are described in the following.
1. AUDIBLE ALARM. The AUDIBLE ALARM will
sound when attempting an incorrect sequence of front
panel programming. This could occur under the follow-
ing conditions:
1. Any two front panel push-buttons are pressed simul-
taneously except the two [VERNIER] push-buttons.
2. The instrument is in FREQ or RATIO or TIME AVG
function and the operator attempts 10 turn the delay on.
3. The instrument is in FREQ or RATIO function and
the operator attempts to turn the AVG function on.
4. The instrument is in rcmolc condition (REMOTE
LED on) and any front panel push-button except
[CLR/LCL] is pressed.
5. The [VERNIER] push-buttons were pressed and the
instrument was not in DISPLAY/MODIFY mode of
operation.
6. The instrument was in DISPLAY/MODIFY tnode of
operation and the [VERNIER fi] or [VERNIER u]
push-buttons were pressed continuously until a parame-
ter limit was reached. Parameter limits are summarized
in Table 3-2.
2. GATE ERROR. The gate error is indicated on the
front panel by the GATE LED. This error will occur
when the counter is in FREQ or TIME AVG function
and when the signal was removed from the input con-
nector in the middle of the measurement process or
when a radiated random noise was sensed by the input
circuitry. The GATE LED will then blink once but no
result will be registered on the display.
3. GATE TIME ERROR. The gate time error is indi-
cated on the front panel by the GT LED. The gate time
erroroccurs in FREQ or TIME AVG functions when the
period of the input signal is larger than the period of the
gate time. The gate error will also occur in Phase A to
B functiou when the gate time is no1 sufficient to permit
the minimum resolution of 1 degrees. When one of the
conditions above occurs. the gate time LED (GT) will
blink for a couple of times and then resume a search
routine. This sequence will rcpcat itself until a proper
signal is found or until the gale time was readjusted to
satisfy the required conditions.
4. TRIGGER LEVEL ERROR. The trigger level error
occurs when the instrument is set to AUTO TRIG or V
PEAK A modes and the input signal is either absent or
below lhe specified auto trigger limils. The trigger level
LED (either TL A or TL B) then blinks. for a couple of
times. The counter 1hen resumes a new search routine.
This sequence will repeat itself until a signal has been
found or until the auto trigger mode was turned off.
3-7. Control Selection
Selecting the various from panel operating modes is
simply a matter of pressing. once or 1wice. the appropri-
ate push-button as dcscribcd in the following para-
graphs.
3-5