Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 20041
Kentech Instruments Ltd.,
Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, U.K.
Tel: 01235 510 748 Fax: 01235 510 722
International tel: (44) 1235 510 748 International fax: (44)1235 510 722
E-mail [email protected]
Kentech Instruments Ltd.
Slow Sweep UnitSTREAK CAMERA
3rd. March 2004
PLEASE READ THIS MANUAL CAREFULLY BEFORE USING
THE SWEEP UNIT.
Serial Number
2
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
DISCLAIMER
This equipment contains high voltage power supplies. Although the current supply capacity is small, careless use
could result in electric shock. It is assumed that this highly specialised equipment will only be used by qualified
personnel.
Kentech Instruments Ltd. accept no responsibility for any electric shock or injury arising from use or misuse of
this equipment. It is the responsibility of the user to exercise care and common sense with this highly versatile
equipment.
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 20043
Figure Captions
Figure 1 The ramp speeds 6
Figure 2 Positive slow ramp generator 7
Figure 3 Negative slow ramp generator 8
Figure 4 Sweep unit, block diagram 9
Figure 5 Sweep unit timing switch (KT106/modified rates) 10
Figure 6 Sweep unit Trigger board (KT101) 11
Figure 7 Slow ramp board showing adjusters 12
Figure 8 Slow ramp layout 13
Contents
DISCLAIMER 2
1 INTRODUCTION 4
1.1 SPECIFICATIONS 4
2 CIRCUIT DESCRIPTIONS 4
3 DATA SHEETS 5
3.1 SWEEP CIRCUIT 5
3.2 TRIGGER DELAYS 5
3.3 BIAS VOLTAGES 5
4
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
1 INTRODUCTION
This manual describes the operation and use of the Kentech Sweep unit. The manual gives the mechanical and
electrical specifications and describes the setting up procedure.
1.1 SPECIFICATIONS
Trigger delay sweep unit ~40ns on the fastest setting, see timing graphs
Number of sweep speeds four
Supply Universal
Sweep Trigger input Normally 10volts, rising in
1ns for minimum delay
8 Volts and 6ns fwhm is just enough to trigger the
unit, but good jitter will require a larger signal.
Sweep hold off time approximately 20ms
Repetition rate 10Hz.
2 CIRCUIT DESCRIPTIONS
The sweep circuit has two separate ramp generators one for the two faster speeds and a second for the two slower ones.
The fast unit is based on two high voltage avalanche step generators unique to Kentech. These two generators provide balanced
steps of amplitude +/- 1.5kV into 100W loads, with a rise time of <1ns. These generators are fed into the sweep leads via 50Wreverse terminating resistors, which reduces the amplitude to > 0.75kV. When this edge reaches the open circuit end at the
sweep plates it doubles up to > 1.5kV. The reverse pulse is absorbed by the reverse terminating resistors. A block diagram of
the unit is shown in figure�5.
Different sweep rates are obtained by the switchable pulse forming LCR network and selected by the two most clockwise
positions of the sweep rate switch (see figure�6). The sweep leads form part of this network and their length must therefore
not be changed.
For the two slower speeds a FET based ramp generator using a Miller integrator is used. This is switched to directly by
the sweep speed selector. The four sweep speeds are selected with the speed selector which switches resistors in the Miller
integrator network. This type of ramp generator is more linear than an avalanche unit and so it is unnecessary to achieve such
high voltages. A result is that the start position has to be closer to the screen edge than the avalanche unit.
A further function of the sweep unit is to provide the required bias voltages to define the start of the sweep (see figure�8).
There are three positions ,”FOCUS”, ”SYNCH” and “OPERATE”. In Focus mode the trigger is inhibited and the bias voltages
set to zero. In Synch. mode the trigger is enabled and the bias voltages are set by the bottom preset on the rear panel. A value
should be chosen that puts the unswept image just on the screen edge. In operate mode the trigger is enabled and the bias
is set by a preset on the rear panel, one for each sweep speed. These have been factory set to the position that ensures optimum
linearity and lack of flyback onto the screen due to oscillations in the ramp generator circuit.
The sweep unit supplies a monitor output pulse which may be used for synchronisation.
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 20045
3 DATA SHEETS
3.1 SWEEP CIRCUIT
This sweep circuit has been set up for non standard sweep rates.
Sweep speeds, nominal.
Speed 1 20 V/ns
Speed 2 40 V/ns
Speed 3 76.3 V/ns
Speed 4 256.5 V/ns
3.2 TRIGGER DELAYS
The time between a fast trigger signal arriving at the trigger input of the sweep generator and the ramp voltage
reaching the voltage which corresponds to screen centre is given below. Further allowance needs to be made for the
time of flight of x-rays from the target to the cathode, for the flight time of photoelectrons from the cathode to the sweep
plates and to any extra cabling between the sweep plates and the leads provided. These figures should be use as a guide
only. They are only valid at the factory set bias settings.
Unit 1
Sweep 1 54.8ns
Sweep 2 46.8ns
Sweep 3 43ns
Sweep 4 39.6ns
For Unit 2 subtract 1ns from the above
For Unit 3 subtract 3ns from the above
3.3 BIAS VOLTAGES
Bias SYNCH user to setfor a tube with a round screen and a deflection requirement of ± 407 volts full
screen we suggest a bias of around ±150 volts.
Bias OPERATE
Sweep Speed 1 300 volts
Sweep Speed 2 350 volts
Sweep Speed 3 436 volts
Sweep Speed 4 700 volts
With these settings the trigger delays above correspond to the time for the ramp to reach the bias voltage, i.e.
screen centre.
6
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
Figure 1 The ramp speeds
Sweep speeds 3 and 4
76.3 and 256.5 V/ns
218V/div, 5ns/div
The steps and oscillations are due to the reflections round the 2
meters of cabling.
It is important to keep the bias low enough that the oscillation on
sweep speed 1 does not retrace the screen.
Sweep speeds 3 and 4
76.3 and 256.5 V/ns
436V/div, 5ns/div
Sweep speed 2
40 V/ns
100V/div, 5ns/div
Sweep speed 1
20 V/ns
100V/div, 5ns/div
Wobbles are due to transit times around
the 2 meters of cable.
Sweep speed 1
ramp balance
Sweep speed 2
ramp balance
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 20047
33
M
VR
68
sho
rt c
ircu
it R
9 a
nd
R10
om
itte
do
mit
ted
om
itte
d
Figu
re 2
Posi
tive
slo
w r
amp
gen
erat
or
8
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
Figure 3
Negative slo
w ram
p gen
erator
0R
omitted
omitted
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 20049
Figu
re 4
Swee
p u
nit
, blo
ck d
iagr
am
Tri
gger
Inpu
t
2 am
p
-1kV
+1k V
Bia
sSw
itch
5 in
vert
ors
+ve
Ste
pG
ener
ator
KT
111/
P
-ve
Step
Gen
erat
or
KT
111/
N
Bal
ance
Mon
itor
Out
put
+2.
5kV
-2.5
kV
500
volts
L N
IEC
filte
r
Ram
pO
utpu
ts
Tim
ing
Switc
h2
off
KT
106
12 v
olt
univ
ersa
lpo
wer
supp
ly
Slow
Ram
pge
nera
tors
±710 for
sw
eeps 5
& 6
±400 for
sw
eeps 1
,2,3
,4
+1.
5kV
& 6
0 V
olts
trig
ger
coun
ter
1,3,
5,8,
10,1
5co
unte
r pr
eset
sw
itch
Tri
gger
and
Mon
itor
KT
101
10
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
Figure 5
Sweep
un
it timin
g switch
(KT
106/mo
dified
rates)
0.27µH220
47
0.68µH0.27µH
4722
INO
UT
fromavalanche
stackto sw
eepoutput
All capacitors approx 8pf , form
edfrom
double sided pcb 15mm
by20m
m
Slow ram
pG
enerator4 speeds only
12 volts
activate HT
toavalanche stacks
activate HT
to Slowram
p generator
Select slow
sweep bias
voltage
Select fast sweep bias
voltage
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 200411
Figu
re 6
Swee
p u
nit
Tri
gger
bo
ard
(K
T10
1)
Mon
itor 22
0
100
100
1n
100V
200V
200V
100p
F
1n
10n
+50
0V
1k2
15V
100
10k
100
* *
100
1n
1n 1n
Tri
gger
Inp
ut O
utpu
ts to
Fas
t Sw
eep
Boa
rds
Sw
eep
bala
nce
* S
elec
ted
Tri
gger
Tra
nsis
tors
To
slow
ram
p bo
ard
160V
160V1k 1k
Pot r
emov
edan
d sh
orte
d
1n
12
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 2004
Figure 7
Slow
ramp
board
sho
win
g adju
sters
Kentech Instruments Ltd., Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxon, OX11 9AG, England.
3rd. March 200413
Figu
re 8
Slo
w r
amp
layo
ut