Monte....How does a Sensitivity Control work ?

[ToddB64]

Hi Monte !

In regard to my subject question, I'm trying to get a correct mental picture of what is actually happening when I turn up the Sensitivity control on a metal detector.

For example, at the bottom of page #10 in the Operator Manual for my Bandido ll uMax, under the sub-title Setting the Sensitivity Level in MAXBoost, it says that in ideal conditions, MAXBoost can add depth to your search, etc.. By that, I get a mental picture of the ubiquitous cone-shaped electromagnetic field (Detection Pattern) elongating into the surrounding matrix as the Sensitivity is increased by the operator, all other factors being acceptable to that happening.

As a side note, is it true that some additional, albeit perhaps trifling, amount of battery power is required to push the field deeper ?

Thanks for the help !

Todd

 

[Monte]

In regard to my subject question, I'm trying to get a correct mental picture of what is actually happening when I turn up the Sensitivity control on a metal detector.

I have to tell you that it will depend upon the make or model detector in question . Let me use a Tesoro Lobo and Bandido II and a White's Gold master Tracker and IDX Pro as examples.

Some models have a Sensitivity control that has a function in an All Metal (conventional) mode and does[/iu] control the Transmit power, such as the Lobo or Gold Master Tracker.

Some models have a factory preset Transmit power level (sensitivity) that is for peak performance in the standard All Metal mode, and the variable Sensitivity control is simply tied in with the motion based Discriminate circuitry, such as with the Bandido II or IDX Pro.

Some models have had a more appropriate title for this Discriminate mode control function than "Sensitivity," such as the White's 5900/6000 Di Pro SL's or XL Pro which have a variable control labeled Signal Balance. On the XLT this function is called Pre-Amp Gain and is perhaps more descriptive of the Sensitivity control found on most detector models. It balances the signal so that you boost it prior to the amplifier circuitry w/o over powering it. The term "Pre-Amp Gain" nicely described that it adjusts the Gain (Sensitivity) Pre- (before) the Amp(lifier) circuitry.

For example, at the bottom of page #10 in the Operator Manual for my Bandido ll uMax, under the sub-title Setting the Sensitivity Level in MAXBoost, it says that in ideal conditions, MAXBoost can add depth to your search, etc.

The clue here is under ideal conditions, and that suggests when hunting areas with limited or no outside RF interference, and with low or moderate mineralization where the detector is going to have rather clean or clear performance and not a lot of "noise" from outside sources, or from "bad ground" mineralized conditions.

You can "add depth" simply because you can boost the gain of the target response before the signal is processed through the amplifying circuitry (Pre-Amp Gain or Signal Balance)

By that, I get a mental picture of the ubiquitous cone-shaped electromagnetic field (Detection Pattern) elongating into the surrounding matrix as the Sensitivity is increased by the operator, all other factors being acceptable to that happening.

First, I have to say (and I do very often) there is no "cone-shaped electromagnetic field" going into the ground. The generated EMF is a radiating field of force all about the Transmit winding and is not directions, as such.

This applies to BOTH a concentric wound coil and a wide-scan (double-d) type coil. There is no "coin-shaped field" (concentric) or "knife-edge" field of force that is generated (transmitted), but in stead we have to look at the reactive portion of the electromagnetic field generated by each coil type. There is a difference in the reactive or responsive portion of the field, and in the case of the concentric wound coil, it sometimes might appear to be somewhat cone shaped, but it really varies from brand-to brand, and model to model,

The Transmitted file d of a model that has that function tied in with the Sensitivity/Gain control, does enhance the appearance of the generated field that is produced and can push the signal a bit deeper into the ground.

But the primary benefit of that control on an All Metal mode (usually found in a nugget-hunting model) is to be able to reduce the power level not increase it, because, as I stated, most detectors are designed with a peak Transmit power setting (or very near to it), and this might be too much transmit power for nugget hunting in highly mineralized ground. Therefore, such a control function allows the user to reduce the Sensitivity in order to gain stability and that improves performance.

With the Bandido II

 

[grumpyolman]

That's amazing stuff. How did you learn this? Not questioning it's validity but wonder where someone would have such specific knowledge about technical things in an electronics application that is atypical to begin with. Say, if it was about radar, loran, SSTV transmitting...it'd be easier to see how and why one would know that. But with metal detectors?? It's such a small specialized niche I am curious how you gained that knowledge.
I think you did a good job of explaining the concept of what makes the sensitivity work so a non-electronics mind can gather what you are trying to say.. Thanks....Jim

 

[silversmith]

Well, I'm not sure I agree with all of monte's soliloquise. If you want to see what a concentric coil radiates like, go find a ball the same size as your loop, cut it half into and sandwich the coil between the two ball halves. Yep, it works equally above the coil as it does below, but has minimal detectability at the sides.
And that's my opinion.

Whoa, it's a good thing we have the spell corrector

 

[ToddB64]

Monte........Thanks for the enlightenment on Sensitivity !

If you don't mind, I would appreciate a few clarifications, questions, etc., as follows:

Some models have a factory preset Transmit power level (sensitivity) that is for peak performance in the standard All Metal mode, and the variable Sensitivity control is simply tied in with the motion based Discriminate circuitry, such as with the Bandido II or IDX Pro.

With the Bandido II

 

[slingshot]

I believe he meant "is not directional".

 

[Monte]

n/t

 

[riverguy]

On the cone shape vs a round shape of the coil field it seems to me that one could map out the reponses of their particular detector.

Mount the detector say three feet above the ground and then carefully plot the height and position of a coin at different locations below the coil. At some point farther away from the coil you will reduce or loose signal and hence be able to plot the physical dimensions of your detector's field of detection and thus determine the shape.

Anyone correct me if they see flaws in this experiment.

 

[ToddB64]

I believe he meant "is not directional".

Hi slingshot .........Yeah, I thought the same thing, but you never know, so I ask for clarification. I see Monte has now confirmed you were correct in ascertaining his meaning.

First, I have to say (and I do very often) there is no "cone-shaped electromagnetic field" going into the ground. The generated EMF is a radiating field of force all about the Transmit winding and is not directions, as such.

This applies to BOTH a concentric wound coil and a wide-scan (double-d) type coil. There is no "coin-shaped field" (concentric) or "knife-edge" field of force that is generated (transmitted), but in stead we have to look at the reactive portion of the electromagnetic field generated by each coil type. There is a difference in the reactive or responsive portion of the field, and in the case of the concentric wound coil, it sometimes might appear to be somewhat cone shaped, but it really varies from brand-to brand, and model to model,

Regarding the field shape talked about in Monte's above paragraphs in quotes, this morning I took another look at the illustrations of generated EMF field in several of my metal detecting books and that helped me to see the overall picture of what Monte is saying, to wit, while the generated EMF field is not cone or parabolic shaped, but rather omnidirectional, the portion of the field that is predominately reactive to the targets we seek can sometimes be somewhat cone shaped. Of course, that same predominately reactive portion of the field is also reactive to the bane of metal detectorist, for example mineralized ground, hence Ground Balancing is used to thwart that problem.

I really appreciate Monte drawing my attention to the fact that it is only the predominately reactive portion of the otherwise omnidirectional EMF field that can sometimes appear to be somewhat cone shaped, but since he emphasized that the reactive portion is only sometimes somewhat cone shaped, that leaves me to believe that the most reactive portion of the field can also take on other shapes. I guess that's an opportunity for a new topic of discussion on the effects of different shapes in the "most reactive-to-targets" region of the EMF field, that is, if anyone thinks there would be merit to that discussion. Anyone ?

I'm waiting on Monte's reply to the rest of the questions & comments in my August 02,2009 01:22 AM post.

Thanks for your reply slingshot.

Todd

 

[Monte]

Monte........Thanks for the enlightenment on Sensitivity !

If you don't mind, I would appreciate a few clarifications, questions, etc., as follows:

Some models have a factory preset Transmit power level (sensitivity) that is for peak performance in the standard All Metal mode, and the variable Sensitivity control is simply tied in with the motion based Discriminate circuitry, such as with the Bandido II or IDX Pro.

With the Bandido II

 

[ToddB64]

On the cone shape vs a round shape of the coil field it seems to me that one could map out the responses of their particular detector.

Mount the detector say three feet above the ground and then carefully plot the height and position of a coin at different locations below the coil. At some point farther away from the coil you will reduce or loose signal and hence be able to plot the physical dimensions of your detector's field of detection and thus determine the shape.

Anyone correct me if they see flaws in this experiment.

Hi riverguy !

I think you might be right. I seem to recall seeing a detailed method (explanation & photos) for doing this on a website some years back. It might have been at Sergei T.'s website : Metal Detecting World.com, but not sure. I looked at the site, but couldn't locate the article, so sent an e-mail to inquire. Will advise you on this asap.

Thanks for your idea !

Todd

 

[ToddB64]

Monte.......My applause for those great explanations ! That gives me enough to chew on for awhile !

You certainly deserve the R & R !

Todd

 

[ToddB64]

On the cone shape vs a round shape of the coil field it seems to me that one could map out the responses of their particular detector.

Mount the detector say three feet above the ground and then carefully plot the height and position of a coin at different locations below the coil. At some point farther away from the coil you will reduce or loose signal and hence be able to plot the physical dimensions of your detector's field of detection and thus determine the shape.

Anyone correct me if they see flaws in this experiment.

Hi riverguy !

I think you might be right. I seem to recall seeing a detailed method (explanation & photos) for doing this on a website some years back. It might have been at Sergei T.'s website : Metal Detecting World.com, but not sure. I looked at the site, but couldn't locate the article, so sent an e-mail to inquire. Will advise you on this asap.

Thanks for your idea !

Todd

riverguy.........and anyone else reading this post. Need your help !

Current status: I sent E-mail to Sergei T. , address: treasurereports@yahoo.com, on August 02,2009 4:08 PM. So far, no reply. Haven't given up though.

If anyone else has recall on where they saw the method, or where it might be located, please post here and I'll check it out. I thought it was on Sergei's site because he has some unusual stuff, but as indicated above, I don't see it listed on his current website selections, so sent E-mail thinking he might have put it in archives.

Todd

 

[ToddB64]

riverguy.........Re my previous post, Sergei's website has not responded to my Email sent three weeks ago and no one else has been able to help us so far. The detailed method & pictures I saw years ago (and don't recall details anymore) was a simple setup that didn't require expensive equipment.

Sorry I haven't been successful in locating the details for you, but if anything pops up, I'll post it here. Maybe in time someone else will come up with something more. In the meantime, there is the method you suggested.......have you tried it ? Did the results look plausible ?

Note to others viewing this message: The above subject entitled "Simple method to determine Coil Field Shape" is a spin-off from the original thread subject. That happens occasionally.

Todd