another three or four probes, all hooked
up to the same system.
Over the split-second duration of the
explosion, the thermometer will
continually sample visible and infrared
optical radiation, taking up to 50,000
measurements/sec. This data is sent to
the main instrumentation part of the
device that is safely situated at the end of
a 100m optical cable. Here the single fibre
is split into four, and the radiation is
passed through optical filters designed to
only pass optical radiation/light at very
particular wavelengths. This allows the
device to separate the light into four
different wavelengths, collecting far more
information about the thermal physics of
the explosion than could be obtained
from one wavelength.
From the filters, the light is passed to
high-speed detectors, which convert
optical radiation into a voltage that can
be related directly to temperature. Sutton
would not be drawn on the full cost of
the system, but said it is relatively
inexpensive, requiring a high-speed data
acquisition system that typically costs in
the region of £2,000, and off-the-shelf
fibreoptic cables.
So far, the system has only been
tested on quite small charges of 5–10g.
However, Sutton is confident that once
tested outside NPL’s pyro-lab the clever
device will survive far bigger
explosions time and again. ‘The thing
about explosions is that although they
are very violent, the actual amount of
energy released isn’t very big. It’s just
‘There’s very little data on conditions at the
centre of an explosion... no-one has ever stuck
something directly inside a fireball’ Gavin Sutton, NPL
that it happens very quickly that does
the damage,’ said Sutton.
‘If the thermometer was put in a
Bunsen flame for a few minutes it
would melt, but because explosions
happen very quickly it survives — we
just need to clean the end off each time,’
he added.
The system, designed to cope with
temperatures of at least 4,000ºC, could
be used to monitor blasts equivalent to
the EnGIneeR 27 OCTOBER–9 NOVEMBER 2008 27
those created by a car blowing up,
said Sutton.
He said the DSTL is using the
equipment to generate reliable
temperature data for its explosion
simulations, and although the
government agency declined to
comment, it is likely the technology
will feed into two of its key areas: the
development of more advanced armour,
and the forensic analysis of bomb
blasts. For example, while the skills of
the agency’s forensic explosives lab in
Kent are called upon whenever explo-
sive material is recovered from a terror
plot, a separate team is researching the
tough lightweight armour that will be a
key component of the British Army’s
next generation of vehicles, the Future
Rapid Effect System (FRES).
INSIGHT
To view a Ceros magazine you need to have JavaScript enabled in your browser and have the flash player 8 or higher installed. To install the latest flash player, click the icon above, install the flash plugin and then click here to refresh this page.