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 50
1
with 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 50
1
. 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 50
1
terminator 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 50
1
cable 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.
