I'm holding out for this dog to assist in the field
https://www.theguardian.com/technology/2016/jun/24/alphabet-robot-dog-cleaning-housebot-spotmini
Or this cat that you could dispatch from the office to scope a job
[MEDIA=youtube]DTVOK2yvbBM[/MEDIA]
I don't know the how or why only that a number of years ago one of the larger firms in the area set rebar over a period of a year or so and most of the rebar they set will not give a tone on the metal detectors. They were set at many different locations with different conditions and times.
They conluded something caused that batch of rebar to loose it's polarity. However the cause was never discovered.
I've taken four rebar from the same bundle and they all had different signal strength. I'm sure location can have a serious impact, but it's not the only cause.
paden cash, post: 419198, member: 20 wrote: I'm going to get all technical on you all here. Most Schonstedt-style locators (two sensor) depend on detecting the differential reading of a magnetic field between the two sensors. One is usually in the tip of the locator, the other at some location up the shaft. Just because there is no great "squeal" over some targets doesn't necessarily mean the target itself lacks any magnetic properties. It merely means the locator cannot detect a difference between the two sensors great enough to oscillate the sought after "squeal".
Granted a null field at both the tip coil and the mid-point coil doesn't return a signal. But I'm sure we're all familiar with the ghost squeal that happens as we walk and search side to side with the locator. Where a signal makes you stop and back up a foot or two and you satisfy yourself it was nothing and then continue.
The point I'm making is there are weak magnetic fields all over and they don't have to emanate from metallic objects. Although most metals with an iron content are prone to possess a field, the water in the ground and vegetation can exhibit weak signatures. Manganese in an alloy can also have a direct effect on the ferrous properties of an object. Even a dry wind blowing over non-ferrous things can create a static charge differential. The earth itself probably has more to do with it than we realize.
If the earth in a specific are has a strong enough cathode (or ground) the weak magnetic field surrounding a ferrous object may be distorted to the point it is almost undetectable to a Schonstedt. If there is aerial electric distribution in the area that is almost certainly grounded there may exist a voltage potential because of the current demand on the distribution system and the ability of the conductors to meet that demand. This can create migrant currents in the ground that will most certainly affect the weak magnetic fields of small ferrous objects in the ground. Ground moisture can also affect current migration through soil. It's probably a helluva lot wetter near the root ball of a crepe myrtle bed than it is out in the middle of a vacant lot.
Although Schonstedt-style locators usually work well and most common rebar has a dependable ferrous signature, the system is not fool proof. I believe the in-situ conditions are a greater factor than we acknowledge. I guess one way to tell would be to remove a length of rebar from the ground that exhibits a null or weak signal from a locator and place that rebar in a different area to see if the it was more the material or the environment in which it rested.
Another yet untried idea I've had over the years would be to employ the services of a canine with a good nose, like a beagle or a bird dog. If you raised it from a pup and had it with you daily, a goodie presented to the animal every time you dug up a pin might instill desire and behavior to "seek" pins (plastic caps or flagging, too). After a little training you could probably just tell the animal to "hunt 'em up" and he or she would go to work for its goodie.
Whether you named the dog "Schonstedt" or "Dip" would probably depend on the dog's other personality traits....;)
To overcome the inherent magnetism/mineralization of the ground...and to obtain that sharp squeal on a desired target, more specialized detectors allow the user to reset a baseline, upon which the signal of the target will be compared. It's called "ground balancing". There is a huge difference between the signal a vertical re-bar gives off vs. one laying on the ground.
The pin finder does not detect alum.
It's likely the alum. cap was shielding the small footprint of a signal the vertical re-bar was giving off. It you were to pull that monument and throw it on the ground, I will bet $100 that it will sound identical to the other one. I would also bet that if you pulled that alum. cap off, you would have a much better signal.
paden cash, post: 419198, member: 20 wrote: I'm going to get all technical on you all here. Most Schonstedt-style locators (two sensor) depend on detecting the differential reading of a magnetic field between the two sensors. One is usually in the tip of the locator, the other at some location up the shaft. Just because there is no great "squeal" over some targets doesn't necessarily mean the target itself lacks any magnetic properties. It merely means the locator cannot detect a difference between the two sensors great enough to oscillate the sought after "squeal".
Granted a null field at both the tip coil and the mid-point coil doesn't return a signal. But I'm sure we're all familiar with the ghost squeal that happens as we walk and search side to side with the locator. Where a signal makes you stop and back up a foot or two and you satisfy yourself it was nothing and then continue.
The point I'm making is there are weak magnetic fields all over and they don't have to emanate from metallic objects. Although most metals with an iron content are prone to possess a field, the water in the ground and vegetation can exhibit weak signatures. Manganese in an alloy can also have a direct effect on the ferrous properties of an object. Even a dry wind blowing over non-ferrous things can create a static charge differential. The earth itself probably has more to do with it than we realize.
If the earth in a specific are has a strong enough cathode (or ground) the weak magnetic field surrounding a ferrous object may be distorted to the point it is almost undetectable to a Schonstedt. If there is aerial electric distribution in the area that is almost certainly grounded there may exist a voltage potential because of the current demand on the distribution system and the ability of the conductors to meet that demand. This can create migrant currents in the ground that will most certainly affect the weak magnetic fields of small ferrous objects in the ground. Ground moisture can also affect current migration through soil. It's probably a helluva lot wetter near the root ball of a crepe myrtle bed than it is out in the middle of a vacant lot.
Although Schonstedt-style locators usually work well and most common rebar has a dependable ferrous signature, the system is not fool proof. I believe the in-situ conditions are a greater factor than we acknowledge. I guess one way to tell would be to remove a length of rebar from the ground that exhibits a null or weak signal from a locator and place that rebar in a different area to see if the it was more the material or the environment in which it rested.
Another yet untried idea I've had over the years would be to employ the services of a canine with a good nose, like a beagle or a bird dog. If you raised it from a pup and had it with you daily, a goodie presented to the animal every time you dug up a pin might instill desire and behavior to "seek" pins (plastic caps or flagging, too). After a little training you could probably just tell the animal to "hunt 'em up" and he or she would go to work for its goodie.
Whether you named the dog "Schonstedt" or "Dip" would probably depend on the dog's other personality traits....;)
I found a case where the power company owned a house and enough acreage to build a substation next to the house. They they subdivided the house from the substation and sold it. The new owner claimed about getting zapped while taking care of business so they sued the power company. This is because some voltage makes it into the ground then travels back to the substation so the ground in the vicinity of a substation can be somewhat charged. The fix to the problem is to isolate all the above ground plumbing in the house from the ground by installing non-metal sections between the in ground cast iron and the above ground pipe.
I'm sure part of the "fix" was also to compensate the new owner for his emotional pain. Imagine wondering if you were going to get zapped every time you used the john.
imaudigger, post: 419346, member: 7286 wrote: I'm sure part of the "fix" was also to compensate the new owner for his emotional pain. Imagine wondering if you were going to get zapped every time you used the john.
Or step on the metal shower drain.
Dave Karoly, post: 419345, member: 94 wrote: I found a case where the power company owned a house and enough acreage to build a substation next to the house. They they subdivided the house from the substation and sold it. The new owner claimed about getting zapped while taking care of business so they sued the power company. This is because some voltage makes it into the ground then travels back to the substation so the ground in the vicinity of a substation can be somewhat charged. The fix to the problem is to isolate all the above ground plumbing in the house from the ground by installing non-metal sections between the in ground cast iron and the above ground pipe.
There is all sorts of things that can happen around power grid appurtenances. One that naturally occurs is a static potential induced by proximity. If you've ever set up an instrument beneath an aerial transmission line on a hot dry day and noticed your hair standing on end; that's a static potential. An example of a current potential that should not occur (but often does) is where an ungrounded fence or open wire telephone lines shared with a power grid on an aerial system induces a potential between the two systems that can be deadly to maintenance workers. Most utilities in close proximity to one another are required to have common grounding and minimum separation. I have seen a measurable (and dangerous) voltage potential between a buried ductile iron water main and a buried electrical primary. There is a good reason most utilities have adopted those minimum separation requirements.
If you ever get the chance take a hand held voltmeter to the field with you and check different things to an earth ground. It might surprise you.
A good definition of stray voltage: https://en.wikipedia.org/wiki/Stray_voltage
There are reasons this occurs naturally (as in the power company isn't culpable) and there are reasons is occurs due to the demand on, and the construction or limitations of the distribution system. There is still ongoing litigation.
imaudigger, post: 419310, member: 7286 wrote: It's likely the alum. cap was shielding the small footprint of a signal the vertical re-bar was giving off
Not true. Aluminum has scarcely any more effect on a static magnetic field (which the Shoenstedt is detecting) than does air.
I just now did an experiment to confirm that. I used a pole barn nail stuck in my yard and then covered it with a stack of scrap sheet aluminum 1/2" thick and several inches wide and long. It made no discernible difference to the GA-52.
With AC and radio frequencies aluminum's conductivity does make it a shield, but that doesn't affect a static field from the earth or iron rod.
Stray voltage. Ask dairy cows how they feel about that.
No joke. A major issue in dairy barns is the opportunity for stray voltage to zap the cows. They tend to give far less milk when their spigots are part of the loop where the stray voltage is flowing.
Holy Cow, post: 419401, member: 50 wrote: Stray voltage. Ask dairy cows how they feel about that.
No joke. A major issue in dairy barns is the opportunity for stray voltage to zap the cows. They tend to give far less milk when their spigots are part of the loop where the stray voltage is flowing.
The bovine female equivalent to guys peeing on electric fences. The former a victim of circumstance and the latter a self-inflicted hilarity. Neither sounds like something I wish to experience.
