Kentech Instruments PBG7 Manual de usuario
Kentech Instruments Ltd.
Notes on the use of
PBG7 pulser system
Serial No. (special)
It is important to read this manual before operating the
system.
2nd April 2004
Caution
PBG7 Pulser System Serial No. xxxxx
This equipment is a scientific research tool that has been intentionally designed to generate
short high energy ultrawideband electromagnetic pulses and the EM emissions will be highly
sensitive to the load applied by the user. It is suitable for use only in a sealed electromagnetic
or laboratory environment, unless it is used in a system that has been verified by the system
builder to comply with EC directive 89/336/EEC. It will interfere with and may damage
sensitive equipment in the local environment. Use of this equipment outside of a sealed
electromagnetic or laboratory environment may result in prosecution. This equipment must
not be used or operated in a domestic environment or as part of a safety critical or life support
system.
With an appropriate load, and when fitted into a suitable 19” rack system that prevents
access to the rear panel connectors, the unit is safe for use by personnel with relevant
technical qualifications and UWB training in a laboratory environment . You are warned
however that the radiation from the system with an antenna or inappropriate load attached
can damage sensitive equipment and corrupt data stored in computer and microprocessor
based systems including aeronautical and other safety critical systems. It can cause terminal
failure of vital medical electronic systems such as pacemakers and other life support systems
and it can inhibit and damage communications systems. The main 45kV 150ps output is likely
to be particularly damaging but the 12kV 100ps and 6kV 100ps outputs must also be treated
with caution.
This equipment is supplied on the understanding that the user will analyse these risks, accept
responsibility for them and take appropriate precautions in the use of this instrument.
The pulse outputs from this pulse generator will destroy most types of power attenuators and
electronic test equipment. It is the users responsibility to ensure that any apparatus connected
to the output is suitably rated.
Kentech Instruments Ltd accepts no responsibility for any damage or liabilities incurred in the
operation of this equipment.
The system contains 120W of 4kV power supplies, this can cause death or injury from burns
and electric shock. Do not remove covers. Return to Kentech Instruments Ltd. for servicing.
Clean only with soft dry cloth.
Check that all relevant connectors are in place on the rear panels before applying ac power.
Do not disconnect the multiway connectors on the rear of the PBG7 45kV output module
and PBG7 HV power supply module for 3 minutes after removing ac power.
The equipment must be grounded via the power connector to maintain protection from
electric shock.
Introduction
This PBG7 system is a state of the art avalanche pulser utilising a series parallel
array of avalanche stacks coupled with various transformers to generate a large single output
amplitude of *45kV into 501.
The instrument consists of five 19” rack mounting modules which should be
mounted into a single 19” enclosure that prevents access to the rear panel connectors. These
are:-
1. PBG7 control and trigger module
2. Four channel delay module
3. PBG5 four channel trigger module
4. PBG7 45kV output module
5. PBG7 HV power supply module
The system can be operated in each of three configurations:-
PBG1 configuration. One output signal is taken from the 6kV output on the PBG7 control
and trigger module, the other four modules are disconnected and not used.
PBG5 configuration. Four output signals are taken from the four 12kV outputs on the PBG5
four channel trigger module. The PBG7 control and trigger module, Four channel delay module
and PBG5 four channel trigger module are used, the other two modules are unused and
disconnected.
PBG7 configuration. One output signal is taken from the 45kV output on the PBG7 45kV
output module. All modules are used except the four channel delay module which should
always remain powered down but must remain in circuit to preserve correct trigger timing.
Note that for each configuration it is necessary to configure both hardware and software - see
below.
The PBG7 control and trigger module is 3U high and contains the microprocessor and low
voltage trigger electronics and a PBG1 type pulse output board generating approx 6kV
amplitude into 501with a risetime <150ps. In PBG5 or PBG7 configurations the output must
be connected using the short N to N type 501conformable cable provided to the internal 4
way splitter. This generates 4 approximately simultaneous trigger signals to be used to trigger
the PBG5 four channel trigger module. The rear panel has a female 9 way D type connector for
RS232 to an optional computer and a male 9 way D connector which is for system control. In
PBG5 or PBG7 configurations the sysytem control should be connected to the PBG5 four
channel trigger module using the screened D to D type lead provided. There are also one IEC
power inlet and two IEC power outlets which should be used to power the PBG5 four channel
trigger module and PBG7 HV power supply module.
The four channel delay module is 3U high and sits between the PBG7 control and trigger
module and the PBG5 four channel trigger module. Except in PBG1 configuration it should be
connected to both these modules using the 8 BNC to BNC cables provided. It’s function is to
allow independent variation of the delay of the 4 trigger signals in PBG5 configuration to allow
beam steering using a 4 element antenna array. In PBG7 configuration the delay module is not
used and should remain connected via the 8 BNC to BNC cables but powered down. This
module is completely independent of the rest of the system, it has it’s own microprocessor with
RS232 connection and power input on the rear panel and no connection to the system control
link.
PBG5 four channel trigger module is 6U high. It has four BNC trigger inputs and four high
voltage HN pulse outputs of approx 12kV amplitude into 501. In PBG7 configuration these
outputs are used to trigger the PBG7 45kV output module using the 4 HN to HN cables
provided. In PBG5 configuration the outputs can be used to drive an antenna array. The IEC
power input must be connected to an outlet on the PBG7 control and trigger module. The 9
way D type control link connectors are daisy chained together, one must be connected to the
PBG7 control and trigger module and one to the PBG7 HV power supply module.
PBG7 45kV output module is 9U high. It has four HN 12kV trigger inputs and one pulse
output of approx 45kV amplitude using a special Kentech connector. On the rear panel are six
multiway connectors and two D type connectors which must be connected to the PBG7 HV
power supply module using the cables provided.
PBG7 HV power supply module is 3U high. The six multiway and two D type connectors on
the rear panel must be connected to the PBG7 45kV output module. The IEC power input
must be connected to an outlet on the PBG7 control and trigger module.
Use
The equipment should be mounted in a suitable 19” rack. The rear panel and front panel
connections should be added depending on the configuration required (PBG1, PBG5 or PBG7)
as shown in the diagram below.
Note that ac power for the PBG5 four channel trigger module and PBG7 HV power supply
module must be taken from the PBG7 control and trigger module using the IEC male/female
leads supplied. The front panel switch will therefore switch power to all three modules. This is
important for the software to power up correctly. The four channel delay module is completely
independent and should have its independent power supply. The external ac power required is
110 to 240V 50 or 60Hz, approx 250W.
The system is air cooled and at maximum repetition rate the air cooled system will dissipate
approximately 250W of thermal power, consequently it requires an adequate and unobstructed
flow of clean air.
RF emission from the circuitry inside the PBG5 four channel trigger module and particularly
the PBG7 45kV output module is severe, the modules rely upon the integrity of their enclosures
to contain the radiation. Further, because of the high power and high frequency requirements
the the modules use their chassis as ground return and screen. Therefore it is important for
correct operation that all covers remain in place, all screws and fasteners remain secure, and the
equipment is earthed via the power lead.
The PBG5 four channel trigger module, PBG7 45kV output module and PBG7 HV power
supply module are controlled and tested by the microprocessor in the trigger unit by means of
the various control and monitor links on rear panels. It is important that all rear panel
connections are configured correctly and all connectors with locking screws are tightened
correctly.
If remote control by RS232 is employed we recommend that only screened cables should be
use and that the cables should be fitted with clamp on ferrites near to the PBG7 system.
The trigger signal can be generated internally or applied externally to the trigger unit. When
external triggering is used, the trigger signal should be *5 volts into 501with a fast rising edge
(<5ns) to maintain the low jitter of the system. Do not trigger the generator at a rate in excess
of 500Hz. The external trigger input is a BNC connector mounted on the front panel. When the
trigger unit is triggered the “triggered” LED on the front panel will flash.
There are an additional “triggered” LEDs on the PBG5 four channel trigger module and PBG7
HV power supply module showing the state of the trigger stacks.
In the internal trigger, single shot and delayed modes there is an internal delay which may be
adjusted by the user. Another front panel BNC connector “pre-trigger output” provides a
signal of ~10V into 501. This is approximately synchronous with the trigger, in advance of the
high voltage pulse output and may be used to trigger auxiliary equipment such as a sampling
oscilloscope. There are thermal drifts in the delay generator which will stabilise after the pulser
has been switched on for ~20 minutes.
The internal trigger generator will only run if the inhibit BNC is shorted, if remote control is not
required this may be conveniently achieved using the 501terminator supplied, plugged onto
the connector.
In “direct” mode the external trigger signal is applied directly to the avalanche stack and the
low level circuitry is bypassed to give the minimum trigger delay. There is no monitor output
generated in this mode.
The main output of the PBG7 45kV output module appears at the front panel connector which
is a special connector of Kentech design. There are drawings of this connector at the rear of this
manual to allow the user to manufacture additional units as required. The pulser will tolerate
open circuit, short circuit and arc loads at the end of a 501cable longer than 1m. However
prolonged operation like this without a resistive load to dissipate residual energy from the pulse
may degrade the lifetime of the insulator in the output connector. This is because the pulse
energy is trapped within the output cable for a prolonged time and may cause partial discharges
which erode the insulation. We believe the worst case scenario from this perspective is a short
circuit at the end of a few nanoseconds of cable.
It is not necessary to have a well matched 501 load to preserve pulser lifetime, but we
recommend the load should present a dc resistive load to the pulser in the range of approx 25
to 100 ohms.
If it is necessary to monitor or characterise the pulse output then suitable attenuators must be
used. The 12kV and 45kV pulse outputs from this unit are capable of destroying most
types of power attenuators and terminators including most of the high pulse power
types.The pulser was characterised at the factory using two methods:-
a) For the 12kV outputs a x2 Kentech suicide T attenuator was followed by two x10 Barth
142-NMFP-20 attenuators then two radial x10 attenuators. These outputs unit will destroy the
Barth 142 if used without the T.
b) For the 45kV output a special x10 Kentech resistive attenuator was used followed by two
x10 Barth 142-NMFP-20 attenuators then two radial x10 attenuators.
See the photographs enclosed in this manual.
The output may be observed with a high bandwidth oscilloscope. This may either be a fast
(>3GHz) single shot type or a sampling type.
If the output of the pulser is to be used directly or via any passive network it is essential that
cable lengths are kept as short as possible and that only high quality cable is used. This will
enable the fast rising edge generated by the unit to reach the load without serious degradation.
The PBG7 is controlled by the microprocessor unit with LCD display and four button keypad.
On power up, the trigger input of the avalanche stack is disabled, note that it is always
necessary to issue commands to the microprocessor unit via the keyboard or the RS232
interface to enable the trigger circuit and make the pulser run normally. Please see the software
section below.
The µP unit includes a self test routine. This should be run at least once a day at power up, or at
any change of configuration and any faults noted, see sections on stack faults and comms faults
below. Otherwise there is no regular maintenance required. There is some redundancy in the
unit by virtue of its design, and the unit may continue to operate at slightly reduced amplitude
with several faults present. The switching elements in these avalanche pulsers generally have a
long life, but their life is finite and therefore it is sensible to switch off the unit or at least not
trigger it when it is not required. It is not possible to write a test routine to find 100% of all
possible faults, so if the unit appears to malfunction, and the procedures below fail to isolate the
problem please contact Kentech Instruments for advice.
There is a facility provided under the Stack Status menu to disable individual stacks. This may
be used in certain circumstances to disable faulty stacks that are causing problems. It is also
permissible to use this facility to disable output stacks to reduce the output amplitude. Note this
information is stored in non volatile memory, ie it will be remembered even when ac power is
removed. If the output amplitude appears low please check under the system status menu that
all 86 stacks are enabled.
IMPORTANT
When fitting the output connector ensure that:
i) all six fixing screws are tightened to maintain a low impedance ground connection
ii) the plastic insulating collar and sprung centre contact are fitted
Failure to fit the fixing screws will result in severe RF emission.
PBG7 V1.0 Software
The microprocessor used is a Hitachi H8/532 running a FORTH operating system and it is
programmed in the FORTH programming language. It is not necessary to have any knowledge
of the H8 or FORTH to operate the pulser.
a) Main menu
On power up or on entering LOCAL mode from remote, the unit will briefly display the
“Kentech Instruments” banner and then the main menu:-
Run... >
Test menu... >
System status... >
Stack status... >
The cursor will be under Run as shown, press the up and down keys to select one of Run,
Test , System status or Stack status then press the right key to execute. While the main menu is
displayed, the serial port is monitored. If the µP receives a character it will enter REMOTE
mode.
b) Run
The display will indicate that the pulser is running and the configuration selected ( see system
status to edit configuration).
<Running
PBG7 Configuration
The HT is switched on to each enabled stack. The trigger is enabled, and the unit will now run
normally while waiting for the user to press a key. All keys are ignored except for left which
causes the trigger to be disabled, the HT to be switched off and a return to the main menu
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