ORTEC 935 Service manual

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i\

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■/

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.