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Please School Me on Magnetometers

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awemawson:
First a little back ground - I need to install land drains in a field that is cris-crossed by cast iron water pipes - some deep some not so deep. The water authorities (both Southern Water and South East Water) don't have accurate plans of where their pipes run, so I thought I'd dig out a little gizmo that I acquired many years ago to see if I could detect them - an ex-military Magnetometer.

I have no idea what application this magnetometer was intended for - but maybe E.O.D. implies Explosive Ordinance Detection  :scratch:

Joules:
Some local metal detecting nut to trace your pipes ?   as long as he doesn't dig them up and claim treasure trove.   :palm:



p.s
     how deep are the pipes ?

If you detect them with that, will they be classed as pipe bombs  :bugeye:

awemawson:
Now the detector head is connected by a cable of about 25 meters, and has a mount for a tripod incorporating an angular adjustment roughly calibrated in degrees of magnetic dip, and even a marker to show the dip angle for the UK.

It is unbelievably sensitive - slightly moving a small screw driver 5 meters from it will trigger its alarm, and I cannot hand hold it still enough for it not to trigger (no I don't have the D T's !). It seems to be sensitive to changing magnetic fields rather than absolute ones, so with the screwdriver waving test, if the screwdriver is stationary the machine electronics returns the meter to zero and the alarm ceases.

I can remember when I got it (at least 15 years ago) mounting it on a tripod and being able to detect cars moving on a road about 1/2 mile away  :bugeye:

I don't think its suitable for my purpose as it's too sensitive and I cannot imagine how I could mount it to move across a field to scan for pipes without the very movement triggering it in the earths magnetic field.

I have always thought that it was intended for nautical use as the lid incorporates a compass bearing engraved lines marked up keel direction, however on reflection it is probably an off the shelf compass so the line are irrelevant.

The electronics looks to be very simple - a dual low power cmos op amp, four logic gates and a couple of transistors, so maybe I could reduce it's sensitiveness electronically, but before I muck it up has anyone come across anything like this before?  What the heck was it for?

awemawson:
Joules,

Conventional metal detectors and CAT (cable avoidance tools) go hay wire as an 11 kV three phase line runs down the field  :bang:

I don't think this unit is going to help me, but really I'm posting to see if anyone knows what it's application originally was  :coffee:

John Rudd:
Andrew,
Go over to the EPE.com forum,
http://www.chatzones.co.uk/cgi-bin/discus/discus.cgi
there are some threads on there about magentometers....some of the guys there might be able to help....you might need to sign up for an account to post your question.....

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