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MODEL 615
ELECTROMETER
OPERATION
a.
Summary of oigital
Outputs
and Controls.
1.
Standard
Output
Codes and Levels.
The stend-
ard output
code for Model 4401 Printer
Output
Cards
is 1-2-4-S
binary
Coded Decimsl
(&Xl).
A binary
coded decimal
digit
is represented
by a four-bit
binary
code as shown in Table
17.
a)
The "ON" state
is defined
as en output
grear-
er then +10 voles
into
a resistance
load of 10 kil-
ohms or greater.
b)
The "OFF" stete
is defined
a9 en outPut
less
than co.4 volts.
TABLE 17.
Decimal
Number
4 bit
3 bit
2 bit
1 bit
0
0
0
0
0
1
0
0
0
1
?
0
0
1
0
3
0
0
1
1
4
0
1
0
0
5
0
1
0
1
6
0
I
1
0
7
0
1
1
1
8
1
0
0
0
9
1
0
0
1
L
c)
Refer
to Figure
19 for e circuit
diagram
of
the Model 4401 Standard
Printer
Output
buffer
stage.
2.
PRINTER/CONTROL Connector.
The PRINTER/CONTROL
Connector
used an the Model 615 provides
for connec-
tions
to 50 pins es Shown in
Table
8.
The mating
connector
supplied
with
Model 4401 is an Amphenol
Part Number 57-30500 or Keithley
Part
Number CS-220,
available
on specie1
order.
3.
Analog-to-Digital
Conversion
Cycle.
a)
The analog-to-digital
conversion
cycle
can
be initiated
in any one of three
ways.
1.
DISPLAY RATE Control
Set at MAX. With the
DISPLAY RATE Control
set at MAX, cbe end of one
complete
conversion
triggers
e second conversion
to obtain
the maximum conversion
rate
of 24 read-
ings per second.
2.
DISPLAY RATE Control
Set at Other Than MAX.
With the DISPLAY RATE Control
set et some posi-
tion
other
than MAX, (uncalibrated
control
set-
ting)
the end of one complete
conversion
triggers
a second conversion
which is delayed
by a speci-
fic
time interval
(DELAY).
The time delay
is a
function
of the position
of a continuously'vari-
able
control
to provide
a conversion
rate
from
24 readings
per second to 2 readings
per minute.
3.
'71OI.D 2" With TRIGGER Control.
With the
"HOLD 2" command grounded,
a closure
to~ground
of
the "TRIGGER" command inLtiac*s
one complete
conversion
cycle.
A second conversion
will
fol-
law only
if
the TRIGGER cormwind is removed and
re-applied
a second time.
The maximum conver-
sion
rate
uslng.an
external
trigger
is 24 read-
ings
per second.
b)
Conversion
Cycle
Timing.
The Conversion
Cycle
is composed of three
timing
periods,
namely,
Integrator
Zero,
Integrator
Sampling,
and A-D
mounting
period.
Refer
fo Timing
Diagram Figure
9.
P
1.
integrator
Zero Period
(ZERO).
When a
trigger
pulse
initiates
a new conversion
cycle,
the Integrator
circuit
is zeroed
for e period
not to exceed 8.33 miilisecands
for 60 SC oper-
ation.
(The Integrator
Zero Period
is 10.00
milliseconds
for 50 Hz operation).
2.
Integrator
Sampling
Period
(INTEGIUTE).
The Integrator
Sampling
Period
follows
automac-
ically
the Integrator
Zero Period
and lasts
for
a duration
of 16.67 milliseconds
for 60 HZ op-
eration.
The Integrator
Sampling
Period
Lasts
for a duration
of 20.00 milliseconds
for
50 ilz
0 pa L ;,ioyil.
*..
3. 'A-D Counting
Period
(COUNT).
The A-D
Counting
Period
is initiated
immediately
follow-
ing the Incegraeor
Sampling
Period.
The actual
counting
time duration
will
depend on the actual
integrator
voltage
up to a maximum of 2000 clock
pulses
or 16.67 milliseconds.
Following
the
counting
period
a Buffer/Storage
command is
auromefically
generated
in order
to store
the
new reading
in the output
registers.
4.
PRINT COMMAND. The PRINT COMMAND signal
is used to trigger
external
printers
or paper
tape punches.
The PRINT COMMAND signal
is de-
layed
10 microseconds
to allow
the storage
leg-
isters
to settle.
The PRINT COMMAND pulse
width
is approximately
100 microseconds
with
e 1 voltl
microsecond
rise
time
into
a 1 kilohm
load.
The
pulse
amplitude
is approximated
by the following
equation:
e, = 14~/(~+2200).
Eq. 2
where R ia the outpat
load resistor.
The "OFF" state
is less
then +0.4 volt
with
ap-
proximately
1 milliampere
sink
current.
NOTE
The date stared
in the Output
Registers
will
not change for
et least
25 milliseconds
for
60 HZ operation.
If
the front
panel
con-
trols
are changed,
the Sensitivity
or Range
SCD output
may be effected.
2-11.
117-234V LINE POWER OPERATION.
The Model 615
is shipped
for use with
117" e-c line
power unless
ordered
for 234V operation.
To convert
eny instrument
for either
117" or 234V operation,
use a screwdriver
to set the 117-234"
Switch
an the reer
panel.
The
0470
17
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