ORTEC 935 Service manual
i\
'
■/
ORTEC
Model
935
Quad
Constant-Fraction
200-MHz
Discriminator
Operating
and
Service
Manual
Model
935
Quad
Constant-Fraction
200-MHz
Discriminator
Operating
and
Service
Manual
U.S.
Patent
No.
4,179,644
Printed
in
U.S.A.
ORTEC®
Part
No.
753770
0503
Manual
Revision
H
Advanced
Measurement
Technology,
Inc.
a/k/a/
ORTEC®,
a
subsidiary
of
AMETEK®,
Inc.
WARRANTY
ORTEC*
warrants
that
the
items
will
be
delivered
free
from
defects
in
material
or
workmanship.
ORTEC
makes
no
other
warranties,
express
or
implied,
and
specifically
NO
WARRANTY
OF
MERCHANTABILITY
OR
FITNESS
FOR
A
PARTICULAR
PURPOSE.
ORTEC's
exclusive
liability
is
limited
to
repairing
or
replacing
at
ORTEC
's
option,
items
found
by
ORTEC
to
be
defective
in
workmanship
or
materials
within
one
year
from
the
date
of
delivery.
ORTEC
's
liability
on
any
claim
of
any
kind,
including
negligence,
loss,
or
damages
arising
out
of,
connected
with,
or
from
the
performance
or
breach
thereof,
or
from
the
manufacture,
sale,
delivery,
resale,
repair,
or
use
of
any
item
or
services
covered
by
this
agreement
or
purchase
order,
shall
in
no
case
exceed
the
price
allocable
to
the
item
or
service
furnished
or
any
part
thereof
that
gives
rise
to
the
claim.
In
the
event
ORTEC
fails
to
manufacture
or
deliver
items
called
for
in
this
agreement
or
purchase
order,
ORTEC's
exclusive
liability
and
buyer's
exclusive
remedy
shall
be
release
of
the
buyer
from
the
obligation
to
pay
the
purchase
price.
In
no
event
shall
ORTEC
be
liable
for
special
or
consequential
damages.
Quality
Control
Before
being
approved
for
shipment,
each
ORTEC
instrument
must
pass
a
stringent
set
of
quality
control
tests
designed
to
expose
any
flaws
in
materials
or
workmanship.
Permanent
records
of
these
tests
are
maintained
for
use
in
warranty
repair
and
as
a
source
of
statistical
information
for
design
improvements.
Repair
Service
If
it
becomes
necessary
to
return
this
instrument
for
repair,
it
is
essential
that
Customer
Services
be
contacted
in
advance
of
its
return
so
that
a
Return
Authorization
Number
can
be
assigned
to
the
unit.
Also,
ORTEC
must
be
informed,
either
in
writing,
by
telephone
[(865)
482-4411]
or
by
facsimile
transmission
[(865)
483-2133],
of
the
nature
of
the
fault
of
the
instrument
being
returned
and
of
the
model,
serial,
and
revision
("Rev"
on
rear
panel)
numbers.
Failure
to
do
so
may
cause
unnecessary
delays
in
getting
the
unit
repaired.
The
ORTEC
standard
procedure
requires
that
instruments
returned
for
repair
pass
the
same
quality
control
tests
that
are
used
for
new-production
instruments.
I
nstruments
that
are
returned
should
be
packed
so
that
they
will
withstand
normal
transit
handling
and
must
be
shipped
PREPAID
via
Air
Parcel
Post
or
United
Parcel
Service
to
the
designated
ORTEC
repair
center.
The
address
label
and
the
package
should
include
the
Return
Authorization
Number
assigned.
Instruments
being
returned
that
are
damaged
in
transit
due
to
inadequate
packing
will
be
repaired
at
the
sender's
expense,
and
it
will
be
the
sender's
responsibility
to
make
claim
with
the
shipper,
instruments
not
in
warranty
should
follow
the
same
procedure
and
ORTEC
will
provide
a
quotation.
Damage
in
Transit
Shipments
should
be
examined
immediately
upon
receipt
for
evidence
of
external
or
concealed
damage.
The
carrier
making
delivery
should
be
notified
immediately
of
any
such
damage,
since
the
carrier
is
normally
liable
for
damage
in
shipment.
Packing
materials,
waybills,
and
other
such
documentation
should
be
preserved
in
order
to
establish
claims.
After
such
notification
to
the
carrier,
please
notify
ORTEC
of
the
circumstances
so
that
assistance
can
be
provided
in
making
damage
claims
and
in
providing
replacement
equipment,
if
necessary.
Copyright
©
2003,
Advanced
Measurement
Technology,
Inc.
All
rights
reserved.
*ORTEG'®
is
a
registered
trademark
of
Advanced
Measurement
Technology,
Inc.
All
other
trademarks
used
herein
are
the
property
of
their
respective
owners.
Ill
CONTENTS
SAFETY
INSTRUCTIONS
AND
SYMBOLS
iv
SAFETY
WARNINGS
AND
CLEANING
INSTRUCTIONS
v
1.
DESCRIPTION
1
2.
SPECIFICATIONS
2
2.1.
PERFORMANCE
2
2.2.
CONTROLS
2
2.3.
INPUTS
3
2.4.
OUTPUTS
3
2.5.
ELECTRICAL
AND
MECHANICAL
4
3.
INSTALLATION
4
3.1.
GENERAL
4
3.2.
CONNECTION
TO
POWER
4
3.3.
INPUT
CONNECTIONS
..
4
3.4.
OUTPUT
CONNECTIONS
4
3.5.
GATING
5
3.6.
OF
SHAPING
DELAY
CABLE
SELECTION
5
3.7.
WALK
SETTING
6
4.
OPERATING
INSTRUCTIONS
6
4.1.
GENERAL
q
4.2.
THRESHOLD
ADJUSTMENT
6
4.3.
OUTPUT
WIDTH
ADJUSTMENT
8
4.4.
CONSTANT-FRACTION
SHAPING
DELAY
ADJUSTMENT
8
4.5.
WALK
ADJUSTMENT
8
4.6.
GATING
ADJUSTMENTS
9
5.
THEORY
OF
OPERATION
g
6.
MAINTENANCE
10
6.1.
CALIBRATION
10
6.2.
TYPICAL
DC
VOLTAGES
io
6.3.
FACTORY
SERVICE
10
IV
SAFETY
INSTRUCTIONS
AND
SYMBOLS
This
manual
contains
up
to
three
levels
of
safety
instructions
that
must
be
observed
in
order
to
avoid
personal
injury
and/or
damage
to
equipment
or
other
property.
These
are:
DANGER
Indicates
a
hazard
that
could
result
in
death
or
serious
bodily
harm
if
the
safety
instruction
is
not
observed.
WARNING
Indicates
a
hazard
that
could
result
in
bodily
harm
if
the
safety
instruction
is
not
observed.
CAUTION
Indicates
a
hazard
that
could
result
in
property
damage
if
the
safety
instruction
is
not
observed.
Please
read
all
safety
instructions
carefully
and
make
sure
you
understand
them
fully
before
attempting
to
use
this
product.
In
addition,
the
following
symbol
may
appear
on
the
product:
ATTENTION
-
Refer
to
Manual
A
DANGER
-
High
Voltage
Please
read
all
safety
instructions
carefully
and
make
sure
you
understand
them
fully
before
attempting
to
use
this
product.
SAFETY
WARNINGS
AND
CLEANING
INSTRUCTIONS
DANGER
Opening
the
cover
of
this
instrument
is
likely
to
expose
dangerous
voltages.
Disconnect
the
instrument
from
all
voltage
sources
while
it
is
being
opened.
WARNING
Using
this
instrument
in
a
manner
not
specified
by
the
manufacturer
may
impair
the
protection
provided
by
the
instrument.
Cleaning
Instructions
To
clean
the
instrument
exterior;
•
Unplug
the
instrument
from
the
ac
power
supply.
•
Remove
loose
dust
on
the
outside
of
the
instrument
with
a
lint-free
cloth.
•
Remove
remaining
dirt
with
a
lint-free
cloth
dampened
in
a
general-purpose
detergent
and
water
solution.
Do
not
use
abrasive
cleaners.
CAUTION
To
prevent
moisture
inside
of
the
instrument
during
external
cleaning,
use
only
enough
liquid
to
dampen
the
cloth
or
applicator.
•
Allow
the
instrument
to
dry
completely
before
reconnecting
it
to
the
power
source.
VI
W
m
a
m
m
ORTEC
MODEL
935
QUAD
200-MHz
CONSTANT-FRACTION
DISCRIMINATOR
1.
DESCRIPTION
The
Model
935
Quad
200-MHz
Constant-Fraction
Discriminator
incorporates
four
separate
and
independently
adjustable
timing
discriminators
in
a
single-width
NIM
module.
Except
where
indicated
otherwise,
the
descriptions
and
specifications
apply
to
each
of
the
four
channels
in
the
module.
The
ability
of
the
Model
935
to
provide
constant-
fraction
timing
on
fast,
negative-polarity
signals
as
narrow
as
1
ns
(FWHM)
makes
it
ideal
for
use
with
microchannel
plates,
fast
photomultiplier
tubes,
fast
scintillators,
and
fast
silicon
detectors.
The
exceptionally
low
walk
delivered
by
the
Model
935
is
vital
in
achieving
the
excellent
time
resolution
inherent
in
these
fast
detectors
over
a
wide
dynamic
range
of
pulse
amplitudes.
The
Model
935
can
also
be
used
with
scintillators
such
as
Nal(TI)
which
have
long
decay
times.
To
prevent
multiple
triggering
on
the
long
decay
times,
the
width
of
the
blocking
output
can
be
adjusted
up
to
1
ps
in
duration.
The
Model
935
uses
the
constant-fraction
timing
technique
to
select
a
timing
point
on
each
input
pulse
that
is
independent
of
pulse
amplitude.
When
properly
adjusted,
the
generation
of
the
output
logic
pulse
corresponds
to
the
point
on
the
leading
edge
of
the
input
pulse
where
the
input
pulse
has
risen
to
20%
of
its
maximum
amplitude.
To
achieve
this
constant-fraction
triggering,
the
input
pulse
is
inverted
and
delayed.
The
delay
time
is
selected
by
an
external
delay
cable
(DLY)
to
be
equal
to
the
time
taken
for
the
input
pulse
to
rise
from
20%
of
maximum
amplitude
to
maximum
amplitude.
Simultaneously,
the
prompt
input
signal
is
attenuated
to
20%
of
its
original
amplitude.
This
attenuated
signal
is
added
to
the
delayed
and
inverted
signal
to
form
a
bipolar
signal
with
a
zero
crossing.
The
zero
crossing
occurs
at
the
time
when
the
inverted
and
delayed
input
signal
has
risen
to
20%
of
its
maximum
amplitude.
The
zero-
crossing
discriminator
in
the
Model
935
detects
this
point
and
generates
the
corresponding
timing
output
pulse.
"Walk"
is
the
systematic
error
in
detecting
the
time
for
the
20%
fraction
as
a
function
of
input
pulse
amplitude.
Minimizing
walk
is
important
when
a
wide
range
of
pulse
amplitudes
must
be
used,
because
walk
contributes
to
the
time
resolution.
The
Model
935
uses
a
patented
transformer
technique
for
constant-fraction
shaping
to
achieve
the
exceptionally
wide
bandwidth
essential
for
processing
input
signals
with
sub-nanosecond
rise
times.
As
shown
in
Fig.
1,
this
results
in
a
walk
guaranteed
<
±50
ps
and
typically
<
±25
ps
over
a
I
00:
1
dynamic
range
of
i
nput
pulse
amplitudes.
The
patented
shaping
technique
also
provides
a
zero-crossing
monitor
output
that
facilitates
quick
and
accurate
walk
adjustment,
because
it
displays
the
full
input
signal
amplitude
range.
1
1
Mi
ll
1
1 1
1
Mi
l l 1
Ml
—
.
<±50
p*
Guaranteed
~
—
♦
—
Actual
Walk
measwed
on
Four
DMorenl
Unite
1
1
1
1 1
1
II
1
1
I
I
I
I
1
I I
1
I
I I
02
0.S
Signal
AmpMutfa
(voNa)
Fig.
1.
Actual
Walk
Measured
on
Four
Different
Units.
See
Walk
Specifications
for
Measurement
Conditions.
The
extremely
short
pulses
from
microchannel
plate
multipliers
and
ultra-fast
photomultiplier
tubes
require
very
short
constant-fraction
shaping
delays.
To
accommodate
these
detectors,
the
Model
935
incorporates
a
selectable
compensation
for
the
inherent
internal
delay.
The
Model
935
includes
a
number
of
controls
which
considerably
broaden
its
utility.
The
threshold
discriminator
is
useful
for
rejecting
low-level
noise.
A
front-panel
test
point
permits
precise
measurement
of
its
setting
in
the
range
from
-20
to
-1
000
mV.
Each
channel
provides
three
bridged,
timing
outputs.
These
are
standard,
fast
negative
NIM
outputs.
The
outputs
can
be
selected
to
have
either
updating
or
blocking
characteristics.
The
updating
mode
is
useful
for
reducing
dead
time
in
overlap
coincidence
experiments.
The
blocking
mode
simultaneously
minimizes
multiple
triggering
and
dead
time
on
scintillators
with
long
decay
times.
The
output
pulse
width
is
adjustable
from
<4
ns
to
>200
ns
in
the
updating
mode,
and
from
<5
ns
to
>
1
ps
in
the
blocking
mode.
The
pulse-pair
resolution
is
<5
ns
at
minimum
pulse
width
in
the
updating
mode.
Switches
on
the
printed
circuit
board
allow
selection
of
which
channels
will
respond
to
the
front-panel
fast-veto
input.
Additional
fast
gating
capability
is
provided
by
individual
gate
inputs
for
each
channel
on
the
rear
panel.
The
mode
of
these
separate
gate
inputs
can
be
individually
selected
to
be
either
coincidence
or
anti-coincidence
via
DIP
switches
on
the
printed
circuit
board.
Each
channel
ran
also
be
programmed,
for
NIM
bins
incorporating
that
signal,
to
ignore
or
respond
to
the
slow
bin
gate
signal
on
pin
36
of
the
power
connector.
2.
SPECIFICATIONS
The
Model
935
contains
four
independent
and
identical
constant-fraction
discriminators.
Except
where
stated
otherwise,
the
descriptions
and
specifications
are
given
for
an
individual
channel,
and
apply
to
each
of
the
four
channels.
2.1.
PERFORMANCE
WALK
Guaranteed
<
±50
ps
(typically
<
±25
ps)
over
a
100:1
dynamic
range.
Measured
under
the
following
conditions:
input
pulse
amplitude
r
ange
from
-50
mV
to
-5
V,
rise
time
<1
ns,
pulse
width
10
ns,
external
shaping
delay
approximately
1.6
ns
(33
cm
or
13
in.),
internal
offset
delay
enabled,
threshold
approximately
20
mV.
CONSTANT
FRACTION
20%.
PULSE-PAIR
RESOLUTION
<5
ns
in
the
updating
mode,
<7
ns
in
the
blocking
mode.
INPUT/OUTPUT
RATE
Operates
at
burst
rates
>200
MHZ
in
the
updating
mode,
and
>150
MHZ
in
the
blocking
mode.
2.2.
CONTROLS
THRESHOLD
(T)
Afront-panel,
20-turn
screwdriver
adjustment
for
each
discriminator
channel
sets
the
minimum
pulse
amplitude
that
will
produce
a
timing
output.
Variable
from
-20
to
-1000
mV.
A
front-
panel
test
point
located
to
the
left
of
the
threshold
adjustment
monitors
the
discriminator
threshold
setting.
The
test
point
voltage
is
10*
the
actual
threshold
setting.
Output
impedance:
<2
kO.
WALK
ADJUSTMENT
(Z)
A
front-panel,
20-turn
screwdriver
adjustment
for
fine-tuning
the
zero-
crossing
discriminator
threshold
to
achieve
minimum
walk.
Adjustable
over
a
±15
mV
range.
A
front-panel
test
point
located
to
left
of
the
walk
adjustment
monitors
the
actual
setting
of
the
zero-
crossing
discriminator.
Output
impedance,
1
k
O.
OUTPUT
WIDTH
(W)
A
front-panel,
20-turn
screwdriver
adjustment
for
each
discriminator
channel
sets
the
width
of
the
three
output
logic
pulses.
The
range
of
width
adjustment
depends
on
the
positions
of
jumpers
W2
and
W3.
TRANSMISSION
DELAY
Typically
<
13
ns
with
1.6-ns
external
delay.
OPERATING
TEMPERATURE
RANGE
0to50°C.
THRESHOLD
TEMPERATURE
SENSITIVITY
<0.01
%/°C,
from
Oto
50°C.
Threshold
referenced
to
the
-12
V
supply
level
supplied
by
the
NIM
bin.
TRANSMISSION
DELAY
TEMPERATURE
SENSITIVITY
<±10
ps/°C
from
0
to
50
°C.
Table
1.
The
Dependence
of
the
Output
Pulse
Width
Range
on
W2
and
W3
Jumper
Positions.
W3
Output
Pulse
Width
Adjustment
Jumper
Range
Position
W2
=
U
W2
=
B
Updating
Blocking
open
<4
to
>100
ns
<5
to
>100
ns
8
<4
to
>200
ns
<5
to
>200
ns
S
+
L
Not
functional
<30
ns
to
>400
ns
B
GATE
ON/OFF
Rear-panel
switch
turns
the
Bin
Gate
on
or
off
for
aii
channels
programmed
to
accept
the
Bin
Gate.
GATE
COIN/ANTI
A
printed
wiring
board
DIP
switch
selects
either
the
coincidence
or
anticoincidence
mode
for
the
individual
channel's
response
to
the
rear-panel
gate
input.
VETO
YES/NO
A
printed
wiring
board
DIP
switch
selects
whether
or
not
an
individual
channel
will
respond
to
the
front-panel
VETO
input.
BIN
GATE
YES/NO
A
printed
wiring
board
DIP
switch
selects
whether
or
not
an
individual
channel
will
respond
to
the
bin
gate
signal.
INTERNAL
OFFSET
DELAY
(Wl)
Printed
wiring
board
jumper
W1
is
normally
omitted
to
enable
the
1.7-ns
internal
offset
delay.
This
delay
compensates
for
internal
delays
and
makes
it
possible
to
implement
the
very
short
shaping
delays
required
with
1-ns
input
pulse
widths.
With
Jumper
W1
installed,
the
minimum
shaping
delay
is
limited
by
a
+0.7-ns
internal
contribution.
With
W1
omitted,
the
internal
delay
contribution
is
effectively
-1.0
ns.
The
Model
935
is
shipped
from
the
factory
with
the
W1
jumper
omitted.
Spare
jumpers
for
this
position
are
located
in
the
storage
area
towards
the
rear
of
the
module.
UPDATING/BLOCKING
MODE
(W2)
The
printed
wiring
board
jumper
W2
selects
either
the
updating
mode
(U
),
or
the
blocking
mode
(B)
for
the
output
pulse
widths.
In
the
blocking
mode,
a
second
input
pulse
will
generate
no
output
pulse
if
it
arrives
within
the
output
pulse
width
W
caused
by
a
previous
input
pulse.
In
the
updating
mode,
a
second
input
pulse
arriving
within
the
output
pulse
width
W
from
a
previous
pulse
will
extend
the
output
pulse,
from
the
time
of
arrival,
by
a
length
W.
The
Model
935
is
shipped
from
the
factory
in
the
updating
mode.
OUTPUT
PULSE
WIDTH
RANGE
(W3)
The
printed
wiring
board
jumper
W3
selects
the
range
of
output
width
adjustment
as
listed
in
Table
1.
The
Model
935
is
shipped
from
the
factory
with
the
W3
jumper
omitted.
Spare
jumpers
for
this
position
are
located
in
the
storage
area
toward
the
rear
of
the
module.
2.3.
INPUTS
INI,
IN2,
INS,
or
IN4
A
front-panel
LEMO
connector
input
on
each
channel
accepts
the
fast
linear
signal
from
a
detector
for
constant-fraction
timing.
Linear
range
from
0
to
-10
V.
Signal
input
impedance,
50
Q,
dc-coupled;
input
protected
with
diode
clamps
at
±10
V.
Input
reflections
<10%
for
input
rise
times
>
2
ns.
GATE
INPUTS
1,
2,
3,
or
4
A
rear-panel
BNC
connectorforeach
channel
accepts
a
negative,
fast
NIM
logic
signal
to
gate
the
respective
constant-
fraction
timing
output.
Coincidence
or
anticoincidence
gating
is
selected
by
a
printed
wiring
board
DIP
switch
(See
GATE
COIN/ANTI).
Input
impedance,
50
Q.
For
proper
gating
operation,
the
leading
edge
of
the
GATE
INPUT
should
precede
the
INI
(IN2,
INS,
or
IN4)
signal
by
1
ns
and
have
a
width
equal
to
the
CF
Shaping
Delay
plus
5
ns.
VETO
A
single,
front-panel
LEMO
connector
accepts
NIM
negative
fast
logic
pulses
to
inhibit
the
timing
outputs
on
all
the
channels
chosen
with
the
VETO
YES/NO
switch.
Input
impedance,
50
0.
For
proper
FAST
VETO
operation,
the
leading
edge
of
the
VETO
signal
must
precede
the
INI
(IN2,
INS,
or
IN4)
signal
by
3
ns
and
have
a
width
e
qual
to
the
CF
Shaping
Delay
plus
5
ns.
BIN
GATE
A
slow
master
gate
signal
enabled
by
the
rear-panel
B
GATE
ON/OFF
switch
permits
gating
off
the
timing
outputs
when
the
Model
935
is
installed
in
a
bin
that
provides
a
bin
gate
signal
on
pin
36
of
the
NIM
power
connector.
Clamping
pin
36
to
ground
from
+5
V
inhibits
operation
of
all
channels
selected
by
the
BIN
GATE
YES/NO
switch.
2.4.
OUTPUTS
CF
SHAPING
DELAY
(DLY)
A
front-panel
pair
of
LEMO
connectors
for
selecting
the
required
constant-fraction
shaping
delay.
A
50-
Q
cable
is
required.
For
triggering
at
a
20%
fraction,
the
length
of
the
shaping
delay
is
approximately
equal
to
the
time
taken
for
the
input
pulse
to
rise
from
20%
of
its
full
amplitude
to
full
amplitude.
CF
MONITOR
(M)
Permits
observation
of
the
constant-fraction
shaped
signal
through
a
LEMO
connector
on
the
front
panel.
Output
im
pedance.
50
Q,
ac-coupled.
The
monitor
output
is
attenuated
by
a
factor
of
approximately
5
with
respect
to
the
input
when
driving
a
terminated
50-
O
cable.
OUT
Three
bridged,
updating
or
blocking,
fast
negative
NIM
output
signals,
furnished
through
front-panel
LEMO
connectors,
mark
the
CF
zero-
crossing
time.
Amplitude
-800
mV
on
50-
0
load.
Each
output
connector
has
its
own
50-
Q
resistor
in
series
with
the
common
output
driver.
GND
Front-panel
test
point
provides
a
convenient
ground
connection
for
test
probes.
EVENT-OCCURRED
LED
Front-panel
LED
for
each
channel
indicates
that
an
output
signal
has
occurred.
2.5.
ELECTRICAL
AND
MECHANICAL
POWER
REQUIREMENTS
The
Model
935
derives
its
power
from
a
NIM
bin
power
supply.
Required
dc
voltages
and
currents
are:
+12
V
at
33
mA,
+
6
V
at
225
mA,
-6V
at
1400
mA,
-12V
at
169
mA,
-24
V
at
55
mA.
WEIGHT
Net
1.1
kg
(2.6
lb).
Shipping
2.0
kg
(4.4
lb)
DIMENSIONS
NIM-standard
single-width
module
3.43
X
22.13
cm
(1.35
x
8.714
in.)
per
TID-20893
(Rev).
3.
INSTALLATION
3.1.
GENERAL
The
Model
935
power
requirements
must
be
furnished
from
a
NIM-standard
bin
and
power
supply
that
includes
±6
V
power
distribution
such
as
the
ORTEC
4001C/4002E,
4001C/4002D,
or
4001A/4002D
NIM
Bins/Power
Supplies.
The
bin
and
power
supply
in
which
the
Model
935
will
normally
be
operated
is
designed
for
relay
rack
mounting.
If
the
equipment
is
rack
mounted,
be
sure
that
there
is
adequate
ventilation
to
prevent
any
localized
heating
in
the
Model
935.
The
temperature
of
equipment
mounted
in
racks
can
easily
exceed
the
maximum
limit
of
50
°C
(323
K)
unless
precautions
are
taken.
3.2.
CONNECTION
TO
POWER
Due
to
the
very
high
speed
electronic
components
used
in
the
Model
935
to
achieve
its
excellent
performance,
the
Model
935
exceeds
the
normal
fair
share
of
power
per
slot
of
normal
NIM
power
supplies.
As
many
as
eight
Model
935s,
a
total
of
32
channels,
can
be
operated
in
a
ORTEC
4002C/4002E
NIM
Bin/Power
Supply.
To
be
sure
of
proper
operation,
check
the
de
voltage
levels
of
the
power
supply
after
all
modules
have
been
installed
in
the
bin.
ORTEC
bins
and
power
supplies
include
convenient
test
points
on
the
power
supply
control
panel
to
permit
monitoring
these
levels.
3.3.
INPUT
CONNECTIONS
Each
discriminator
channel
includes
an
input
connector
on
the
front
panel
that
is
terminated
internally
in
50
D.
Connect
the
source
of
negative
input
signals
to
this
connector
through
a
50
D
coaxial
cable
and
a
mating
LEMO
connector.
Any
of
the
four
channels
can
be
provided
with
an
input
signal
and
will
operate
independently
from
all
other
channels.
3.4.
OUTPUT
CONNECTIONS
There
are
three
output
connectors
for
each
channel.
These
connectors
furnish
three
identical,
simultaneous,
negative
NIM
logic
signals
for
each
input
pulse
that
exceeds
the
adjusted
threshold
level.
The
output
pulse
width
can
be
adjusted
by
the
front-panel
W
control
associated
with
that
channel.
When
operating
in
the
updating
mode,
the
range
of
width
adjustment
can
be
increased
by
adding
a
PWB
jumper
to
the
"8"
pins
at
W3.
When
operating
in
the
blocking
mode,
the
range
of
width
adjustment
can
be
increased
by
adding
jumpers
to
either
or
both
the
"8"
and
"L"
pins
at
W3.
Each
output
connection
should
be
furnished
through
a
mating
LEMO
connector
and
a
50-
0
coaxial
cable
to
a
50-
Q
load
impedance.
For
best
results,
terminate
all
unused
output
connectors
in
each
active
channel
with
a
50-
D
terminator
on
the
front
panel.
Termination
is
not
necessary
for
unused
channels.
3.5.
GATING
Each
channel
of
the
Model
935
can
be
externally
gated
by
one
of
three
conditions.
A
front-
panel
Veto
input
can
block
the
output.
Each
channel
can
be
separately
gated
by
rear-panel
Gate
inputs.
A
NIM
bin
signal,
the
B
(bin)
Gate
operating
through
pin
36
of
the
power
connector
in
the
NIM
bin,
can
inhibit
an
output,
providing
that
the
rear-panel
B
Gate
switch
is
set
to
On.
The
gating
conditions
for
each
channel
of
the
Model
935
are
controlled
by
PWB
DIP
switches.
The
Veto
input
can
be
selected
as
either
Yes
or
No,
the
Gate
input
can
be
selected
as
either
Coincidence
or
Anticoincidence,
and
the
B
Gate
can
be
selected
as
either
Yes
or
No.
For
proper
gating
operation,
certain
timing
conditions
must
be
satisfied
between
the
leading
edge
of
the
input
signal
and
the
gating
signal.
When
using
the
front-panel
fast
Veto
i
nput,
its
leading
edge
should
precede
the
input
signal
by
3
ns,
and
its
width
should
be
equal
to
the
OF
shaping
delay
plus
5
ns.
When
using
the
rear-panel
Gate
input,
its
leading
edge
should
precede
the
input
signal
by
1
ns,
and
its
width
should
be
equal
to
the
CF
shaping
delay
plus
5
ns.
The
B
(bin)
Gate
signal
is
a
slow
logic
signal,
and
it
must
overlap
the
input
signal
to
be
effective.
3.6.
CF
SHAPING
DELAY
CABLE
SELECTION
The
CF
shaping
delay
for
each
channel
is
adjusted
by
selecting
an
appropriate
length
of
50-
Q
coaxial
cable
and
adding
it
between
the
two
Delay
(DLY)
LEMO
connectors
on
the
front
panel.
The
length
of
cable
determines
the
amount
of
external
signal
delay
that
is
added
to
the
internal
delay
to
constitute
the
total
constant-fraction
shaping
delay.
Since
the
Model
935
is
equipped
with
a
jumper-
selectable
internal
offset
delay,
the
external
CF
shaping
delay
will
depend
on
the
position
of
internal
jumper
W1.
With
jumper
W1
removed
(placed
in
the
storage
area
at
the
rear
of
the
PWB),
the
total
constant-fraction
shaping
delay,
t<j,To,ai),
is
approximated
by
td(Totai)
~
td(Extemai)
"
1-0
OS,
W1
rcmoved.
(3.1)
Wo'ai)
~
^d(Extemai)
^.7
OS,
W1
in
place.
(3.2)
The
primary
usage
of
the
Model
935
is
expected
to
be
in
fast
timing
or
counting
experiments
with
scintillators
and
photomultiplier
tubes
(PMTs)
and
Silicon
Surface
Barrier
Detectors.
In
these
applications,
the
CF
Shaping
Delay
t^doiai)
'S
selected
so
that
the
zero-crossing
of
the
bipolar
timing
signal
occurs
just
as
the
peak
of
the
attenuated,
undelayed
portion
of
the
CF
signal
has
reached
its
maximum
amplitude.
Thus,
the
zero-
crossing
occurs
at
the
same
fraction
of
the
input
pulse
height,
regardless
of
the
amplitude
of
the
input
signal.
Selection
of
the
CF
Shaping
Delay
for
best
timing
performance
with
a
given
scintillator
and
PMT
is
usually
accomplished
experimentally.
The
r
andomly
generated
signals
from
the
anode
of
the
PMT
are
applied
to
the
input
of
one
channel
of
the
discriminator.
Each
of
the
two
CF
Delay
connectors
should
be
terminated
with
a
50-
Q
terminator.
The
CF
Monitor
signal
can
be
observed
on
a
fast
oscilloscope
(bandwidth
>
300
MHZ),
which
is
terminated
in
50-0
and
triggered
internally.
The
Monitor
signal
represents
the
attenuated,
undelayed
portion
of
the
constant-fraction
signal
with
no
delayed
signal
subtracted
from
it.
The
addition
of
the
appropriate external
CF
Shaping
Delay
t(,,E^grnai)
causes
the
resulting
bipolar
signal
at
the
CF
Monitor
to
cross
the
baseline
at
the
peak
of
the
attenuated,
undelayed
signal.
When
using
the
internal
offset
delay
(i.e.,
jumper
W1
removed),
a
useful
formula
for
the
initial
trial
selection
of
the
CF
Shaping
Delay
is
td(Extemat)
=
T
+
1.0
ns,
W1
removed,
(3.3)
where
T
is
the
time
for
the
leading
edge
of
the
pulse
to
rise
from
20%
of
maximum
amplitude
to
maximum
amplitude.
The
20%
number
corresponds
to
the
20%
triggering
fraction
designed
into
the
Model
935.
With
jumper
W1
in
place
(i.e.,
when
not
using
the
internal
offset
delay),
a
useful
formula
for
the
initial
trial
selection
of
the
CF
Shaping
Delay
is
Wxtemai)
=
T
-
0.7
ns,
W1
in
place.
(3.4)
In
normal
operation,
jumper
W1
is
removed
and
placed
in
the
storage
area
at
the
rear
of
the
PWB.
This
setting
will
work
properly
for
all
input
signals.
The
Model
935
is
shipped
with
jumper
W1
in
the
storage
area.
For
input
signals
having
rise
times
greater
than
2
ns,
jumper
W1
can
be
used
to
short
the
internal
offset
delay,
allowing
for
shorter
external
CF
Shaping
Delays.
3.7.
WALK
SETTING
The
Walk
adjustment
is
a
front-panel,
20-turn
screwdriver
adjusted
potentiometer
for
each
channel.
A
Walk
Monitor
front-panel
test
point
is
used
to
monitor
the
actual
setting
of
the
dc
zero-
crossing
adjustment.
A
nominal
value
for
this
dc
level
is
+1.5
mV,
but
the
optimal
value
is
best
determined
experimentally.
Walk
adjustment
can
be
accomplished
while
observing
the
delayed
CF
Monitor
signal
on
a
fast
oscilloscope
(bandwidth
>300
MHZ),
which
is
triggered
externally
by
the
output
signal
of
the
Model
935.
The
Walk
potentiometer
(Z)
should
be
adjusted
so
that
the
bipolar
constant-fraction
signals
for
all
amplitudes
cross
through
the
baseline
at
approximately
the
same
time.
Figure
3(a)
shows
the
anode
signals
from
a
Hamamatsu
1332
PMT
with
a
12.9-cc
BC418
truncated
cone
scintillator
exposed
to
a
®°Co
source.
Figure
3(b)
shows
the
delayed
CF
Monitor
signal
triggered
by
the
Model
935
output
signal
with
the
walk
properly
adjusted.
Adjusting
the
Walk
potentiometer
counterclockwise
results
in
the
waveform
shown
in
Figure
3(c),
where
the
extra
line
near
the
baseline
indicates
leading-edge
timing.
Proper
Walk
adjustment
can
be
achieved
by
adjusting
the
Walk
potentiometer
counter-clockwise
to
obtain
the
waveform
shown
in
Figure
3(c),
then
turning
the
Walk
adjustment
clockwise
to
just
eliminate
the
leading-edge
timing
line.
An
additi
one!
1
to
2
turns
clockwise
should
give
the
waveform
in
Figure
3(b)
and
optimum
walk
adjustment.
The
final
optimization
of
the
Walk
adjustment
is
best
accomplished
by
optimizing
the
symmetry
and
minimizing
the
width
of
the
coincidence
peak
in
the
time
spectrum
(see
Section
4).
4.
OPERATING
INSTRUCTIONS
4.1.
GENERAL
The
actual
timing
performance
of
a
timing
system
depends
on
many
variables.
The
type
of
detector
and
the
energy
range
of
interest
are
two
important
system
variables
that
are
indepen
dent
of
the
electronics.
In
general,
detectors
having
fast
rise
time
signals
and
higher
energies
give
the
best
timing
performance.
A
simple
timing
system
is
shown
in
Figure
4.
This
system
consists
of
two
detectors
each
with
their
own
high
voltage
supply,
two
Model
935
CFDs,
a
Delay
unit
for
timing
calibration
and
signal
offset,
a
Time-to-Amplitude
Converter
(TAG)
and
a
multichannel
analyzer
(MCA).
Also
shown
is
a
Preamplifier
(PA),
a
spectroscopy
amplifier
(Amp),
and
a
Gate
and
Delay
Generator
(GDG)
used
for
energy
calibration.
The
detectors
shown
in
Figure
4
consist
of
fast
scintillators
mounted
on
fast
photomultiplier
tubes
(PMTs).
Each
PMT
is
connected
to
a
PMT
Base
for
distribution
of
the
high
voltage.
Care
must
betaken
in
preparing
and
mounting
the
scintillator
to
ensure
very
efficient
coupling
between
the
scintillator
and
the
PMT.
The
high
voltage
setting
for
the
PMT
depends
on
the
type
of
PMT,
and
the
manufacturer
of
the
PMT
should
be
consulted.
The
gain
of
the
PMT
depends
directly
on
the
value
of
the
high
voltage
and
provides
a
convenient
method
for
adjusting
the
output
signal
amplitude
from
the
PMT.
In
general,
the
high
voltage
s
hould
be
set
sufficiently
high
to
ensure
a
large
signal
input
to
the
CFD.
However,
the
high
voltage
should
not
be
set
so
high
as
to
cause
the
onset
of
saturation
in
the
PMT.
The
final
adjustment
of
the
high
voltage
is
a
compromise
that
can
best
be
determined
experimentally.
4.2.
THRESHOLD
ADJUSTMENT
The
Model
935
will
produce
an
output
signal
each
time
the
input
signal
crosses
the
threshold.
Setting
the
threshold
is
equivalent
to
setting
the
lowest
energy
of
interest.
While
it
is
possible
to
set
the
threshold
using
an
oscilloscope,
a
far
more
accurate
method
is
to
use
the
actual
detector,
a
radioactive
source,
and
an
MCA
gated
by
the
Model
935.
A
Gate
and
Delay
Generator
is
used
to
convert
the
Model
935
output
to
a
signal
suitable
for
gating
the
MCA.
To
adjust
the
threshold
level,
measure
the
dc
voltage
from
the
front-panel
Threshold
monitor
test
point
to
ground
for
the
active
channel.
The
Threshold
monitor
test
point
is
located
to
the
left
of
the
threshold
potentiometer
on
the
front
panel.
A
convenient
ground
test
point
is
located
at
the
Fig.
3.
(a)
Anode
signal
from
PMT
and
scintillator,
(b)
the
Model
935
CF
Monitor
signal
showing
proper
walk
adjustment,
and
(c)
the
Model
935
CF
Monitor
signal
showing
improper
walk
adjustment.
See
text
for
discussion.
HV
DYNODE
SCINTILLATORS
HV
ANODE
BASE
PMT
PMT
BASE
SOURCE
DYNODE
935
Start
TAC
MCA
ANODE
935
■DELAYl
Slop
GDQ
To
MCA
Gate
To
MCA
'npul
Signal
Used
to
Calibrate
lire
935
Thresliold
Fig.
4.
A
Simple
Timing
System.
bottom
of
the
front
panel
to
the
right
of
the
Veto
input
connector.
The
nominal
range
of
voltages
at
the
Threshold
test
point
is
-200
mV
to
-10
V,
corresponding
to
the
actual
threshold
which
is
10%
of
the
test
point
voltage.
Use
a
screwdriver
to
set
the
threshold
level
with
the
control
marked
T.
4.3.
OUTPUT
WIDTH
ADJUSTMENT
To
adjust
the
output
width,
provide
an
input
pulse
that
exceeds
the
adjusted
threshold
at
a
rate
less
than
0.5
MHZ
and
observe
the
width
of
an
output
pulse
from
any
of
the
three
output
connectors.
Terminate
the
other
output
connectors
in
50
Q.
Use
a
screwdriver
to
set
the
control
marked
W
for
the
output
width
in
the
active
channel.
When
operating
in
the
Updating
mode, the
output
width
can
he
adjusted
from
<4
ns
to
>100
ns.
Adding
a
PWB
jumper
to
the
S
position
of
W3
changes
the
range
of
adjustment
to
>200
ns.
W
hen
operating
in
the
blocking
mode,
an
additional
jumper
can
he
added
to
the
L
position
of
W3,
increasing
the
Blocking
output
width
to
>
1000
ns.
4.4.
CONSTANT-FRACTION
SHAPING
DELAY
ADJUSTMENT
Selection
of
the
initial
value
for
the
CF
Shaping
Delay
is
described
in
Section
3.6.
For
input
signals
having
widths
approaching
1
ns,
it
is
necessary to
fine
tune
the
CF
Shaping
Delay
to
achieve
optimum
performance.
The
optimum
value
is
determined
for
a
given
detector
using
the
timing
system
shown
in
Figure
4.
Repeated
measurements
of
timing
resolution
FWHM
and
FWHM
are
made
as
a
function
of
CF
Shaping
Delay
length
to
determine
the
optimum
value
of
the
CF
Shaping
Delay.
4.5.
WALK
ADJUSTMENT
To
adjust
the
Walk
characteristics,
connect
the
signal
source
to
he
used
to
the
Input
connector
in
the
active
channel
and
connect
the
signal
from
the
constant-fraction
Monitor
connector
to
a
fast
oscilloscope
(bandwidth
greater
than
300
MHZ)
through
a
50-D
delay.
Select
the
CF
Shaping
Delay
according
to
the
information
in
Section
3.6.
The
constant-fraction
shaped
si
gnal
can
he
observed
on
the
oscilloscope,
triggered
by
an
undelayed
output
signal
from
the
active
discriminator.
Adjust
the
Walk
(Z)
control,
which
sets
the
zero-crossing
reference,
so
that
the
bipolar
constant-fraction
signals
for
all
input
amplitudes
cross
through
the
baseline
at
approximately
the
same
time.
The
adjacent
test
point
can
be
used
for
resettability
of
the
zero-crossing
reference.
Under
most
operating
conditions,
the
dc
voltage
level
at
the
test
point
should
be
in
the
range
from
-1.0
mV
to
+2.0
mV.
Use
a
screwdriver
to
adjust
the
Z
control.
4.6.
GATING
ADJUSTMENTS
The
gating
conditions
for
each
channel
of
the
Model
935
are
set
by
PWB
DIP
switches
located
near
the
rear
panel
of
the
Model
935.
The
DIP
switches
located
nearest
the
top
of
the
module
set
the
Gate
input
to
operate
in
either
the
Anticoincidence
mode
or
the
Coincidence
mode.
In
the
Anticoincidence
mode,
a
Gate
input
that
satisfies
the
timing
conditions
relative
to
the
Input
signal
blocks
the
output
of
that
channel.
In
the
Coincidence
mode,
a
Gate
input
enables
the
output
of
that
channel.
If
no
Gate
input
is
to
be
used,
place
the
DIP
switch
in
the
Anticoincidence
position.
The
middle
set
of
DIP
switches
controls
the
front-panel
fast
Veto
input.
With
the
DIP
switch
corresponding
to
a
given
channel
in
the
On
position,
the
fast
Veto
signal
can
block
or
veto
the
output
of
that
channel,
providing
that
the
timing
conditions
of
the
fast
Veto
input
relative
to
the
Input
are
satisfied.
The
lowest
set
of
DIP
switches
controls
the
bin
gate
input.
The
bin
gate
DIP
switches
are
effective
only
K
the
rear-
panel
B
Gate
switch
is
in
the
On
position.
With
the
B
Gate
switch
in
the
On
position,
and
the
DIP
switch
in
the
On
position,
a
bin
gate
blocks
the
output
of
the
corresponding
channel,
provided
that
the
timing
conditions
relative
to
the
input
signal
are
satisfied.
The
timing
conditions
for
all
the
gating
inputs
are
described
in
Section
3.5.
5.
THEORY
OF
OPERATION
Figure
5
is
a
simplified
block
diagram
of
the
instrument
that
can
be
used
as
a
reference
to
describe
how
it
operates.
An
input
of
0
to
-10
V
amplitude
starts
at
time
zero
and
is
applied
to
the
50-
O
Splitter.
One
output
of
the
Splitter
is
delayed
by
the
internal
offset
delay
DL1
before
it
is
applied
to
the
leading-edge
arming
discriminator
(LEAD)
and
the
CP
attenuator,
ATTN.
The
ATTN
circuit
sets
the
constant-fraction
attenuation
factor
of
f
=
0.2,
and
its
output
is
applied
to
the
transformer,
XFMR.
The
second
output
of
the
Splitter
is
delayed
by
the
external
CF
Shaping
Delay
and
applied
to
the
second
input
to
the
XFMR.
The
XFMR
output
is
a
bipolar-shaped
signal
whose
zero-crossing
time
is
used
to
derive
the
Model
935
output.
This
signal
is
amplified
by
the
constant-fraction
amplifier
(CPA)
prior
to
being
connected
to
the
zero-crossing
gate
Gl.
The
LEAD
has
an
adjustable
threshold,
ranging
from
-20
mV
to
-1
V,
that
determines
the
minimum
input
signal
amplitude
that
is
required
to
produce
an
output
pulse
from
the
Model
935.
If
the
input
signal
exceeds
the
LEAD
threshold,
that
comparator
produces
an
output
pulse
that
arms
zero-crossing
gate
G1.
The
timing
logic
signal
from
gate
G1
triggers
a
fast
one-shot,
comprised
of
an
ECL
type
D
master-
slave
flip-flop
FF1
and
a
stretcher
circuit.
All
gating
input
signals
are
ORed
by
G2
and
applied
to
the
D
input
of
FF1.
One
output
of
FF1
drives
A2,
which
controls
the
front-panel
event
LED.
The
other
output
of
FF1
drives
the
stretcher
circuit,
which
controls
the
width
of
the
output
signals.
The
output
driver
circuit
provides
a
fast
voltage
output
signal
that
is
capable
of
driving
three
50-
0
loads
simultaneously
with
NIM-standard
negative
fast
logic
pulses.
The
output
signals
are
either
updating
or
blocking,
depending
on
the
setting
of
PWB
jumper
W2.
The
dc
power
requirements
are
shown
in
the
specifications
in
Section
2.
The
power
levels
are
+6
V,
-6
V,
+12
V,
-1
2
V,
and
-24
V,
and
they
are
all
obtained
directly
from
the
bin
power
supply.
10
Veto
(FP)
Gate
(RP)
THRESHOLD
—Cll
OLI
>-'
-v\£vV^
Input
O—
CF
Shaping
DeJay
n
CF
Mon
O-
>
Q
R
Update
A
W3
i
1
£
STRETCH
DRIVER
A3-H000107
A2-HST0107
Outputs
r—WV-o
L-AW-o
Blocking
WALK
Fig.
5.
Simplified
Block
Diagram
of
One
Section
of
the
Model
935.
6.
MAINTENANCE
6.1.
CALIBRATION
Most
adjustments
to
the
Model
935
are
made
via
front-panel
controls.
The
only
internal
adjustment
is
the
Threshold
Gal
potentiometer,
R.
Should
recalibration
be
required,
connect
a
5G-mV,
20-ns-
wide
signal
to
the
input
of
the
section
being
adjusted.
Adjust
the
front-panel
Threshold
potentiometer
such
that
the
front-panel
Threshold
Test
Point
reads
500
mV.
Adjust
the
Threshold
Gal
potentiometer
so
that
the
Model
935
output
half-
fires.
6.2.
TYPICAL
DC
VOLTAGES
All
voltages
listed
on
the
schematic
drawing
are
measured
with
respect
to
ground,
with
the
Threshold
and
Width
controls
set
at
minimum,
and
the
Walk
set
at
+
1.5
mV.
6.3.
FACTORY
SERVICE
This
instrument
can
be
returned
to
the
ORTEG
factory
for
service
and
repair
at
a
nominal
cost.
The
ORTEG
standard
procedure
for
repair
ensures
the
same
quality
control
and
checkout
that
are
used
for
a
new
instrument.
Always
contact
Gustomer
Services
at
ORTEG
before
sending
an
instrument
for
repair
to
obtain
shipping
instructions
and
so
that
the
required
Return
Authorization
Number
can
be
assigned
to
the
unit.
This
number
should
be
written
on
the
address
label
and
on
the
package.
11
Table
2.
Bin/Module
Connector
Pin
Assignments
For
Standard
Nuclear
Instrument
Modules
per
DOE/ER-0457T.
Pin
Function
Pin
Function
1
+3
V
23
Reserved
2
-3
V
24
Reserved
3
Spare
bus
25
Reserved
4
Reserved
bus
26
Spare
5
Coaxial
27
Spare
6
Coaxial
*28
+24
V
7
Coaxial
*29
-24
V
8
200
V
dc
30
Spare
bus
9
Spare
31
Spare
10
+6
V
32
Spare
11
-6
V
*33
117
Vac
(hot)
12
Reserved
bus
*34
Power
return
ground
13
Spare
35
Reset
(Sealer)
14
Spare
36
Gate
15
Reserved
37
Reset
(Auxiliary)
*16
+12V
38
Coaxial
*17
-12V
39
Coaxial
18
Spare
bus
40
Coaxial
19
Reserved
bus
*41
117
Vac
(neutral)
20
Spare
*42
High-quality
ground
21
Spare
G
Ground
guide
pin
22
Reserved
Pins
marked
(*)
are
Installed
and
wired
in
ORTEC's
4001A
and
40010
Modular
System
Bins.
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