What Are Timings?

[oldmancoyote1]

Detector settings are sometimes called timings.  Why?  How can thinking about timings help me configure my detector

[Aureous]

Timings refer to a Pulse Induction detector's code. The long string of code that a PI metal detector needs to use is often called a 'Pulse train' whereby the fractions of a second in each pulse need to have a switch on and switch off sequence. The switch on is a transmit phase and then a switch off is a receive phase. The various gaps between these, the sampling speed and the frequency determine the ability of the entire detector. Each individual string (train) of code for each purpose that the detector is designed for, is called a 'Timing'. For instance, on the GPX5000, you have timings for 'Fine', 'Sharp', 'Normal', 'Sensitive Smooth' etc. Each of these sets of code is designed to achieve a different capability on the detector. The word 'Timing' is used because the Pulse Induction detector type is referred to as a 'Time domain' detector. Time refers to the  switch on-switch off sequence (so that a single loom coil can be used for both transmit AND receive), whereby a VLF or IB metal detector is termed a 'Frequency Domain' metal detector which requires 2 looms, one for transmit and one for receive. Hope my rambling makes some sense....

[Prickly Prospector]

In laymans terms..

Shorter timing...Shallower/smaller gold

Longer timing gives deeper penetration but less sensitivity on small targets..

 

 

[Valens Legacy]

1 hour ago, oldmancoyote1 said:

Detector settings are sometimes called timings.  Why?

Every person that goes detecting has to understand when to have their next drink after digging for an hour to reach that buried aluminum can. Then after the drink when to start detecting again and have another drink to stop the shakes. This goes on for about 4 hours or so or when the person passes out. Then the hunt is over and you can either sleep it off or call a taxi to go home.

That's timing.

[Lead Detector]

16 minutes ago, Valens Legacy said:

drink after digging for an hour to reach that buried aluminum can

Hmmmm, I know that story well . ?

[Steve Herschbach]

The bare basics of PI is the pulse delay. VLF is called Frequency Domain because it is frequency based. Pulse Induction is called Time Domain because it is time based. VLF continuously transmits and receives at a given frequency or frequencies. PI transmits, pauses, then receives. The pause is the Pulse Delay and varies in length - time. A current is induced in targets during the transmit phase, and the induced eddy current is what is picked up in the receive phase. This induced current rapidly decays - weakens - until it is gone. Different targets decay at different rates. Most ground and hot rocks decay faster than metal items. By setting the pulse delay long enough, you can ignore ground while still detecting those metal targets in the receive phase. Many PI detectors have a simple knob variable control that allows you to vary the pulse delay, and therefore what the machine picks up and ignores.

Small targets and low conductive targets decay the fastest and so get eliminated first. The more conductive and larger the target, the longer it retains the eddy currents. There is no ferrous vs non-ferrous and ferrous is treated mainly based on size which in turn governs how long it retains eddy currents.

It all revolves around time - how long is the pulse delay? Then Minelab came up with dual channel PI where you have two channels each running different delays at different times. It was not much of a leap for them to start calling these different mixes of channels and pulse delays "timings."

This is a picture of the White's TDI Pro control set, pulse delay in middle left, range from 10uS to 25uS (microseconds)

[cudamark]

When you say that "different targets decay at different rates" I assume this is based on the size of the target more than what metal the target is made of? If not, it seems to me that with some creative electronics and programming , you could come up with a discriminating PI. You also stated that Minelab came up with the dual channel PI. I always thought that White's did that. Interesting.

[Steve Herschbach]

19 hours ago, cudamark said:

When you say that "different targets decay at different rates" I assume this is based on the size of the target more than what metal the target is made of? If not, it seems to me that with some creative electronics and programming , you could come up with a discriminating PI. You also stated that Minelab came up with the dual channel PI. I always thought that White's did that. Interesting.

No, White's never had a dual channel (two ground balance points) PI. Bruce Candy invented it and it became the basis for Minelab's SD2000 when White's passed on a chance to buy the tech from Bruce. One of the worst decisions in detector history. The TDI was licensed from Eric Foster much later in a bid to catch up, old school single channel. Garrett was actually second with dual ground balance channel PI with the Infinium, then ATX and now Axiom. A really great explanation from an actual engineer instead of me....

https://www.detectorprospector.com/topic/559-interview-with-brent-weaver-senior-design-engineer-garrett-metal-detectors/

PI discrimination based on eddy current decay is as old as PI and inherent in the tech. Every model with a pulse delay control is a "discriminating PI" and some companies like Garrett have marked and sold the control as a disc control for a long time. This is old stuff and if it were so simple as programming a few things it would have been done ages ago. Normal PI disc as employed with eddy current delay is based on both size and conductivity and even shape. You can only speak in generalities. There are huge amounts of overlap on target types and only useful in site specific situations with a knowledgeable operator. Ground balancing PI has a secondary form of discrimination based of the ground balance setting. The conductivity id is depth limited but the tones based GB disc goes to full depth. Fisher gave this a go with the Fisher Impulse AQ using the ground balance as a disc control instead of ground balance.

Still you are basically correct that with high speed signal processing and comparison of the results of the two different id information streams available (Conductivity and GB Comparative) there is a lot more than can be done with PI disc in electronics. Right now it can be done by people who understand all this stuff by using audio and control manipulation, but 90% of the time VLF users are upside down and backwards in their thinking as regards PI disc. I don't know how many times I have heard people who don't know say the systems are depth limited and set up various straw man arguments about why PI disc is useless, when in fact it is being used all the time. Just ask anyone detecting for relics at Culpepper about PI vs VLF and how good a person can get at cherry picking targets at depth. Let alone guys like me that can cherry pick the vast majority of gold nuggets out of trashy old mining locations.

I almost give up explaining it anymore but did make one last attempt at bringing all my posts over the years together into one linked set. It actually requires study and thought to understand as well as tossing all VLF preconceptions. For anyone who wants to give it a go, here it is. You have to read the entire thread plus the links I provided to get the whole picture.

 

Now what AlgoForce brings to the table with the E1500 is advancing the Conductivity ID into giving us a 0-99 numeric reading, vastly improving on the Minelab blanking system and Garrett grunt system. This will probably be depth limited but will give a much finer degree of information one can use to make decisions. Coins in particular should give steady consistent readings. However, it may not be any better than a good multifrequency as far as depth. The dual tones the E1500 produces on the other hand will give two classes of targets to full depth very similar to the Minelabs, Garretts, and TDI. By using both in conjunction I anticipate a step forward in melding both deep target and shallow target id capability in a PI, but again the VLF naysayers should just ignore and be happy. I'm fed up with that lot. I will not debate with anyone how useful any of this is or not. I simply want to use my tools to full capability, not convince others they need to use them.

[Steve Herschbach]

Just to clarify for people who don't know what dual channel and single channel PI is all about. Early PI did not ground balance per se, they relied on the pulse delay to take out the ground and saltwater. This was insufficient however for real bad ground commonly encountered by gold prospectors. I think it was Eric Foster who came up with the first widely sold PI with an actual ground balance. A simple knob as seen on the TDI which was originated in Erics Goldscan models.

Unfortunately a PI ground balance setting creates a huge "hole" where certain targets get eliminated at common ground balance settings. Like 1/4 oz nuggets and certain gold rings for example. Bruce Candy came up with the idea of having two ground balances, each one creating a "hole" at different locations on the scale. The two "channels" as he called them were compared, and if one channel lost an item in the hole the other found it, and by comparing the two channels properly targets missed by single channel systems were revealed. This is all explained by Brent Weaver in the first link I gave in the last post.

Single channel single ground balance PI creates two classes of targets based on the ground balance setting. Dual channel can create three classes.

The early Minelabs actually has two separate ground balance controls that separates them from machines like the TDI. Then Minelab and Garrett learned to manipulate both channels simultaneously for better results. Yet the ability to manipulate the dual channels separately was lost, and I may have to pick up an old SD2100 to be able to play more directly with this stuff.

Again, this is all explained in much greater detail at the second link I provided above.

From the SD2100 manual: