General Information - Keithley 776 Instruction Manual

General Information
l-l. Introduction
This manual provides operating and maintenance infor-
matron
for the Model
716
Programmable
Counter/Timer. Section 1 is a general description of the
instrument. Section 2 and 3 obtain installation and op-
erating instructions. IEEE programming is explained in
Section 4. Maintenance and performance checks are
provided in Section 5. The theoF of operation is de-
scribed in Section 6. Section 7 oullines calibration and
troubleshooting procedures. Section 8 contains tables of
replaceable parts. Section 9 contains schematic and
component location diagrams.
Model 776 is a Fen digit microprocessor based fully-
programmable. three-channel Universal Counrcr I
Timer. The instrument mcasurcs with a vev high reso-
lution and precision the following paramctcrs: Frc-
quency A. Frequency B. Frequency C. Period A. Pulse-
width. Time interval A to B. Total counts B. Ratio A/B.
Ratio C/B. Phase A to B and Amplitude peaks. An
averaging function is available for improved resolution
in time measurement: resohes intervals of pica sec-
onds. Various repetitive tests. no matter how complex.
are greatly simplified b>~ utiliziog any of the IO pre-pro-
grammed front panel set-up. Set-ups are stored in a
non-volatile memory and can be recalled by a simple
ke.s stroke.
Model 776 utilizes a combination of two measure-
ment techniques in order to always achieve maximum
display resolution. Some functions. such as Frequent!
measurement function. can be displayed with up to ten
digits. Such resolution can be gained from frequencies
as low as 0.01 Hz to more than 225 MHz. The reciprocal
technique is being used in low frequency mcasurcmcnts.
up to exactly 120 MHz. where the measurement tcch-
nique is changed to conventional measurement tcch-
nique. Model 776 measures frcqucncies of input signals
with minimum resolution of nine digits in one second
of gate time. With the TCXO
time
base of the Model
776l2.46. the displayed result in largely enhanced. both
in terms of stability and accuracy.
In Model 776. the lraditionally featured decade
steps of gale times. are replaced by a more flerible
variable gate time. This feature permits a choice from
500 internally pre-selected gate interwls. or an! ester-
nal gate intcnal which is applied to a rear panel BNC
conneclor. Internal gate times range from 100 ps to IO
s. External gate expands this range to 1000 s. Trigger
leveI my be selected maounll~~ or left to bc aulomali-
call? adjusted. by the instrument. to the optimum level.
thus eliminating false lriggcring on unknown signals.
NOTE
This manual provides a complclc dc-
scription of all fcrturcs of the 776
Series. Therefore. several of the fea-
tures that are described in the follow-
ing paragraphs may not be installed
in your instrument.
1-2. Instrument Identification
These KeithIcy' instmmcnts are identified by a serial
number. which is located on lhe rear panel. The lvo
most significant digits (Txs) identify instrumcnl modi-
I-I