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Fisher Impulse AQ Calibration Procedure


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That little nail in a capsule is indeed routinely  used for the iron reject tests during the functional certification of the Impulse in factory  but the main reason why it is joined in the package is to be used by the user as a common iron reference target when adjusting the tone/mute modes in the field before starting a session in disc mode.

The operator manual defines the correct iron reject adjustment using that 'reference iron target'. This is the best procedure to get the most of the iron reject function. (see extract below)

The capsule is there to avoid the nail to rust and react differently over time.

5.7 REJECT Control

The REJECT control determines the amount of iron rejection. It applies to TONE, MUTE, and VOLCANIC SAND modes.

A high REJECT level also rejects high conductive targets like larger silver coins; rarely even gold items (such as a large heavy ring) can fall in this range. REJECT should be used only when there is an abundance of iron.

REJECT is best adjusted with an example target you want to reject. A sample iron nail is included with the Impulse AQ Limited.

1. Choose TONE, MUTE, or VOLCANIC SAND mode.

2. Set the REJECT control to 0 and the ATS control to 8.

3. Put the reference iron target on the ground in horizontal position.

4. Swing the coil over the target at a height of around 3 inches while slowly increasing the REJECT control.

5. Stop when the nail responds as follows:

a. In TONE mode: the iron response is mostly low tone with some minor high tone mixed in.

b. In MUTE mode: the iron response is mostly silent with some minor high tone breaking through.

c. In VOLCANIC SAND mode: the iron response is fully silent which is necessary to reject volcanic ground.

6. Optionally, test a US nickel to verify that it gives a high tone.

In setting up iron rejection, both the ATS and REJECT controls affect each other and should be mutually adjusted to achieve the desired rejection responses.

It is highly recommended that rejection is set in the field using test targets. (see Expert REJECT control)

NOTE: The REJECT feature of the IMPULSE AQ does not function in the same way as the discrimination control on a VLF detector. It provides variable audio masking of iron targets as well as high-conductivity targets. Also, unlike some PI detectors, there is no target hole.

5.8 Expert REJECT Control (ATS + REJECT)

1. Choose TONE, MUTE, or VOLCANIC SAND mode.

2. Set the REJECT control to 6 and the ATS control to 0.

3. Put the reference iron target on the ground in horizontal position.

4. Swing the coil over the target at a height of around 3 inches while slowly increasing the ATS control. (Your setting is normally arrive near the position 8, between the position 7 and 😎

5. Stop when the nail responds as follows:

a. In TONE mode: the iron response is mostly low tone with some minor high tone mixed in.

b. In MUTE mode: the iron response is mostly silent with some minor high tone breaking through.

c. In VOLCANIC SAND mode: the iron response is fully silent which is necessary to reject volcanic ground.

6.Finally refine your setting, decrease the REJECT button to obtain an iron response low tone with some minor high tone mixed in.

7. Optionally, test a US nickel to verify that it gives a high tone.  

In setting up iron rejection, both the ATS and REJECT controls affect each other and should be mutually adjusted to achieve the desired rejection responses.

It is highly recommended that rejection is set in the field using test targets.

NOTE: Your IMPULSE AQ takes about 10 minutes after start up to stabilize in temperature. Consequently after this time it is recommended to re-adjust the settings slightly.

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38 minutes ago, phrunt said:

So the QED is getting almost the same depth in it's lowest gain 1/10 in goldenoldies test than the AQ is in an air test on a nickel while using a significantly smaller coil?  Seems weird.  It does seem all the PI's are pretty equal.

This last piece of Willy's post is also interesting, the same thing with the QED, takes it 10 or so minutes to warm up then you are meant to adjust settings and ground balance if necessary....  Similar components I guess.   See below also I'm hoping the "readjust" typo isn't in the actual manual 🙂

 

This extract was indeed taken from an early version of the manual. I do not know if this 'tiny' mistake is still in there.

In the certification document:

3. US Nickel Depth min. = 15.5 inches (in factory)
4. Gold Ring Depth min. = 16.5 inches (in factory)

7. US Nickel Depth min. = 16 inches (air test)
8. Gold Ring 18K, 2.7 grs, size 8, Depth min. = 17 inches (air test)

Note the word 'min.' in the QC results.

The QC tests are made on the PCB alone on a test bench and during the functional tests at the end of the assembly line by QC personnel.

They expects a CLEAR SIGNAL response and the tests are made in a noisy (both EMI and external sound) factory, not in the field. The purpose of this test is to certify that the whole system gives its MINIMUM specs, not its MAXIMUM specs.

They are not detectorists.

A real detectorist using a good quality headphone would react on much less clear sounds.

The real practice has proven that these specs are extended by one or two inches in fair ground and in the hand of a real detectorist.

So, please do not jump to too early conclusions☺️😉

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I might be wrong, but just to be sure of the settings effectiveness, I believe that before to go on the field, this test should be done after those 10 minutes warm up...

At that point I can be sure that the machine will react in a certain way with the knobs in a certain position...And I will hunt with peace of mind during future sessions...

Great informations however...I just don't know how to be now...If sad, cause there's not yet a release time at the horizon or happy cause I'm gradually learning how to use this machine without even touching it...

 

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In my laboratory (a little noise but less than inside the factory):

3. US Nickel Depth min. = 17.5 inches (in my laboratory air tests)
4. Gold Ring Depth min. = 18 inches (in my laboratory air tests)

By JOE on wet sand :

3. US Nickel Depth min. =    >19+  inches (on wet sand)

 

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21 minutes ago, Skullgolddiver said:

I might be wrong, but just to be sure of the settings effectiveness, I believe that before to go on the field, this test should be done after those 10 minutes warm up...

At that point I can be sure that the machine will react in a certain way with the knobs in a certain position...And I will hunt with peace of mind during future sessions...

Great informations however...I just don't know how to be now...If sad, cause there's not yet a release time at the horizon or happy cause I'm gradually learning how to use this machine without even touching it...

 

No

This iron reject procedure should be made on the spot you are going to survey and not at home before going there. The ground type influences the results.

The warm-up  does not changes the conditions as much as the ground.

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4 minutes ago, Willy said:

This iron reject procedure should be made on the spot

In my case I'll keep inside an harness pocket that iron nail and set everything underwater...

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Just so people know there is no actual published owners manual and none comes with the Impulse AQ at this time. It may be helpful to new AQ owners for First Texas to finish the owners manual, so information like this can be in new users hands.

Here is a preliminary set of instructions courtesy of Rick Kempf.

It should also be noted that air tests are nice for calibration and reference information to make sure a detector is operating to factory specification, but that what counts in a PI is how it handles and performs in actual ground conditions. A detector that has exceptional air tests may not in fact be the best performer in the ground. For instance, high frequency VLF detectors air test the best, but generally have lower mineralized ground penetration than lower frequency models. Never assume that what air tests the best will perform best in the ground, and that goes doubly so for extreme ground conditions.

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IMO, forget using that sample "nail" they give you. Find a common one where you are detecting and use that in your test and adjustment procedure. I found there was quite a bit of difference between the two in my settings. Deep, rusty and bent nails still sound good in my tests regardless of settings. Same with hairpins and bottle caps if you still want good tones and depth on small gold (in my tests only. still haven't found gold in the wild yet). 

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8 minutes ago, cudamark said:

IMO, forget using that sample "nail" they give you. Find a common one where you are detecting and use that in your test and adjustment procedure. I found there was quite a bit of difference between the two in my settings. Deep, rusty and bent nails still sound good in my tests regardless of settings. Same with hairpins and bottle caps if you still want good tones and depth on small gold (in my tests only. still haven't found gold in the wild yet). 

Whatever iron target you use, execute the procedure I described to adjust the iron reject.

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