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Widget Of The Week
Eddyprobe II ECT Material Integrity Monitor, 1975?
 There are a number of unfamiliar initialisms* in this episode of
dustygizmos
and I freely admit to having to look them up, often without becoming very much
wiser. So we’ll kick off with a couple of the key ones relating to this
Eddyprobe II Material Integrity Monitor featured here.
The first is ECT or Eddy Current Tester; it’s one of several
techniques used in science and industry to inspect for flaws or measure the
characteristics of conductive materials – more about that in a moment. The next
one is NDT or Non-Destructive Testing. This one is self-explanatory and in
other words, means a method of testing materials without damaging or destroying
them, which is a good thing when you want to make use of whatever it is you are
testing…
Back to ECT and it’s a fairly old idea. Much of the credit for it belongs
to Michael Faraday and his experiments in electromagnetism the 1830s. ECT is
based on the fact that electromagnetic fields change when brought close to
metallic objects. It’s a bit like the way metal detectors work, but with a
great deal more precision, and in this instance the detector head or probe is
usually in direct contact with the object or material concerned.
 In the absence of any sort of hard facts or a user
manual, it seems highly likely that the Eddyprobe II is designed to use a range
of probes that can check the thickness of materials and search for flaws in
welds and coatings and so on. The probe that came with it almost certainly
houses a small coil (according to my test meter it has a resistance of 1.5
ohms). Inside the case, in addition to the front panel meter (scaled ‘%
Calibrated Depth’) and controls, there are two circuit boards; one is marked
‘Detection’ the other ‘Alarm’. The detection board appears to be an oscillator
whilst the alarm board has four op-amp chips (741s). These would be used to
analyse the signal coming from the probe, generate a reading for the front
panel meter and set a level or threshold that illuminates a small lamp when a
particular value has been exceeded. This is all guesswork please so feel free
put me right or fill in the gaps.
 The controls on the front panel comprise a rotary switch, to turn
it on, select power supply option (external DC or internal batteries – four 9
volt PP6 types), and the operating mode. Two potentiometers are used to set
zero on the meter and adjust sensitivity, and on the far right there’s a variable
capacitor labelled ‘Lift Off’. The purpose of most of them is fairly clear but
Lift Off remains a bit of a mystery. The probe connects to the main unit using
a mini BNC socket and on the underside of the sturdy metal case there’s a
socket and switch for an external DC supply and a folding bench stand.
It is impressively well made. The circuit boards are hand
assembled and the internal wiring looms are impeccable, neatly tied and as good
as anything you’ll see on a high quality vintage precision instrument. That is
exactly what it is and it is clear from the number of preset controls and test
points on the two boards, which suggest that it requires a fair amount setting
up and calibration before it can be used in anger.
 I came across this
Eddyprobe II at a South London car boot sale a couple of years ago. It was in
its original box with a shipping label dated June 1980 and that, and the electronic
components it uses is responsible for the guessimated manufacturing date of
1975. It was in apparently as-new condition. The stallholder said that a few
people had taken it out and had a look at it but they, like him (and me), had
no real idea of what it was for. The front panel meter drew me to it. It’s a
distinctive high-quality type made by Sifam and appeared to be identical to the
ones used in Mini Instruments Geiger Counters. I just happened to have one at that
time that was in need of a replacement. The one on the Eddyprobe appeared to be
in excellent condition with the needle moving freely, though the only real way
to test it would be to remove it from the case. These meters can be hard to
come by and cost upwards of £20 second-hand and even though it would be a bit
of a gamble anything less than that would make it a worthwhile purchase. I was
particularly pleased therefore when the stallholder offered it to me for a
fiver!
 The instrument was in outstanding condition and looked as though
it had rarely, if ever been used but unfortunately it came without a user
manual or any documentation. Before I scavenged it for parts I thought it right
and proper to find out a little more about it. Sadly there was almost nothing
about it on the web, apart from a few references to the manufacturer Inspection
Instruments (NDT) London. Most of what I was able to glean was based on the few
tidbits picked up from the Internet and by powering it up to see what it
does. After a fair amount of fiddling I
reckon I managed to figure out the rudiments – with apologies to seasoned ECT
and NDT specialists. My rudimentary test consisted of a thin strip of steel
sprayed with several layers of paint of varying thickness and placed on small
groups of nuts and washers,
Following a lot of trial and error the set up procedure seems to
involve placing the probe on the surface of the material to be checked and
zeroing the meter (it is incredibly sensitive), then, slowly moving the probe over
the surface of the material whilst observing the movement of the meter. There
was a definite twitch either side of zero at the points where the paint layers
varied, and much larger deflections as it passed over the areas where the nuts
and washers were placed. Admittedly it was a far from scientific test but at
the very least it suggested that it is working and gave a hint at how useful it
would be in the hands of a experienced and knowledgeable operator. For the
record although the meter was in tip-top condition the unusual offset-centre
zero configuration made it unsuitable for easy transplantation into a Geiger
Counter.
What Happened To It?
ECT is still widely used for NDT but modern instruments are vastly
more accurate and sophisticated thanks to computerisation and a lot of digital
jiggery-pokery. There is now a vast array of increasingly specialised methods
of NDT involving acoustics, X-Rays, lasers, magnetic flux, magnetic particles,
microwaves, neutrons, thermal and infrared, to name just a few.
In it's day the Eddyprobe II was probably one of the go-to pieces of kit for a wide range of
NDT applications but it doesn’t seem to have done Inspection Instruments Ltd. of
32 Duncan Terrace London much good. I found only a few brief references to the
company on the web, nothing about their history or any other products. What little
there is tapers off in the mid 1980s suggesting they were either taken over or they went out
of business.
When new it must have cost several hundred pounds, possibly a great deal more
with a full set of probes. Today, and in spite of it apparently being in good
working order, it's value lies mosly in the worth of the parts it contains and the £5.00 I paid for it
is probably only a little less than it would fetch on ebay. I cannot see
collectors of vintage scientific instruments getting overly excited by it, even
though it is, apparently, quite rare, but as with most of the other exotic, unusual and plain weird scientific and
industrial artefacts featured in dustygizmos, this may end up being its one and
only appearance on the web, which, hopefully, someone somewhere may find useful
or interesting.
*Apologies for being
a bit nerdy. Initialisms, as opposed to acronyms -- e.g. NASA etc.-- are the ones you can make words out of…
DUSTY DATA
First Seen: 1975?
Original Price: £?
Value Today: £10.00? (0320)
Features: Eddy Current Tester (ECT),
interchangeable probe, '% calibrated depth' scaled meter, variable sensitivity and Lift Off controls, alarm indicator, carry handle, folding bench stand
Power req: 4 x PP6 9 volt battery & external DC adaptor
Dimensions: 206 x 140 x 160mm
Weight: 2.2 kg
Made (assembled) in: England
Hen's Teeth (10 rarest): 9
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