So whats the story with Troy's Shadow??

[Unregistered]

JC1

Hey Mrand,

You talking to me?

Ha Ha , I did explain it.

You just didn't get it.

That's alright. But you do learn more if you dig more.

so to speak.

The board was "laid out" for a 1 uf 50 v polyester cap.

Someone "changed their mind"

The "Masters" screwed up. Thats all.

That's OK.

Time for a new model anyway.

every 6 months.

One change.

new model.

Got to have the "new Model".

X7

[Unregistered]

JC1

Hi Mrand,

Didn't mean to sound so rude.

Picking at the "designer/s" a bit.

Not you.

Tesoro Eh.

Thanks for the information.

You are already having to repair the tough X5?

Guess the op amp is tlv2262.

Have to look it up.

Thanks again. Bit of an inside joke.

Between others.

anyway, my opinion now thats all.

So any idea why the "change was made"

I'll look but still don't think more than

9 volts on the cap.

could be wrong

i guess

usually am.

[Unregistered]

JC1

Hi Mrand,

Ok. it is a tlv2262 and it was selected for its

1 pA input (low current leakage) for lower drift

in an "Integrator circuit" with the switch open.

With the switch closed it is a "leaky integrator"

[Unregistered]

JC1

Hi Mrand,

Well, without the circuit I could only guess

at why the "change was made" based on the

differences between the two capacitors.

first I guessed diaelectric absorption perhaps.

I was wrong. I was such an Idiot, these

"designers" don't even know what that means

then I guessed temperature stability

I was wrong. I was such an Idiot, these

"designers" don't worry about that.

cheapest cap out there.

but now being able to see the circuit.


what the answer is, is Insulation Resistance.

which is nice because it is easy to "explain".

(I should have known it was something simple)

1 pA op amps sounds nice, but to realize this

requires some thinking.

You see 1volt on the board at 1 pA implies

1 tera ohm (1,000,000,000,000 ohm) between

any point on the board and the input of the op amp

or you ruin the low bias current.

you can also do it with things like AC blocking

capacitor which has an insulation resistance

of less than 1 Tera ohm.

A high voltage cap with have a greater resistance

than a low voltage capacitor because the plastic

material is thicker.

the capacitor is also larger.

so depending on how much DC voltage this cap is

blocking from the previous stage depends on how

much this circuit is going to drift.

because the insulation resistance of this cap

is probably also NOT 1 tera ohm.

therefore the cap is determining the drift

and NOT the op amp, so probably could of

used a different op amp with more input bias

current and not noticed it (nice try) but needs this

cap.

so if the board is laid out for a smaller cap.

were any of these smaller cap detectors sold?

get out of the shop?

hope not.

[Goodrat]

Mrand, did you get my email?

?

[Unregistered]

JC1

Hi Mrand,

So, looked up the b-series panasonic polyester caps

1 uf would be 0.03 Tera ohms min so at 1 volt blocking

would be 33 pA. much more than the op amp.

See why it was changed.

the replacement is right at 1 Tera ohm so equal to

op amp 1 pA.


A pure polypropylene would be 30 Tera ohms so

0.03 pA and much less than op amp

Yea, we like to get inside and keep some of these

guys honest.

So whats up with the resistor?

Is that a patch too?

Did everybody get a resistor?

Mixed Reviews?

Could be.

[Unregistered]

JC1

Hi Mrand,

I like puzzles.

What is on the other side?

[Unregistered]

JC1

By the way there is a better way to do

this. but i'm not fixing it.

[Goodrat]

Mod

Keep in mind that ther was a factory mod that was done on the first 300 units. Some of what we see may be that.

[Unregistered]

JC1

Hi Goodrat,

I will keep that in mind.

I did not know that.

How did you?

Too much fun. Ok, I will shut up.

Get em posting.

Oh and Carl you don't have to do the

dielectric absorption stuff

Just kidding.

I will do it.

In the interest of "learning".

Oh and quit posting like this.

Too much fun. I retired. Now I get paid

for doing nothing.

And I got paid a big amount for a job a while

back. finially.

And I shorted Sniffex

And nobody corrected my spelling.

Did you look it up?

diaelectric?

not bunnie? rat?

here you go.

get you started.


Best of Bob !!!!!


Dielectric absorption can cause subtle errors in analog applications such as those employing S/H circuits, integrating ADCs and active filters. But knowing how to measure this soakage and compensate for it helps you minimize its effects.

Nowadays, you're more likely to notice the effects of dielectric absorption in some more subtle way, perhaps in the performance of an integrator that can't be reset to zero or a sample/hold that refuses to work correctly. But whether you literally feel its effects or merely observe them in a circuit's behavior, dielectric absorption is an undesirable characteristic that every capacitor possesses to some degree. This characteristic is inherent in the dielectric material itself, although a poor manufacturing procedure or inferior foil electrodes can contribute to the problem.

http://www.national.com/rap/Applicat...570,28,00.html

[robert]

Come on..


Mrand Hi !
Very interesting so far!
Why dont you post the rest of schematic here?
I do not think is gonna harm anybodys feelings...oposite...is gonna be a great
to have that schematic!
I was acused that only asking something for free....well, whats wrong with that? This is the place for that...a lot of nice schematics already here...
Many thanks in advance!
regards to all!

[digger barns]

so where can i get troy shadow schematic

[Goodrat]

Schematic

I think after someone say's they have one, the men in black show up in the middle of the night and take them away!

[kt315]

hi Mrand!
can you speak TX coil in this X-5 is of parallel or serial resonanse type? or maybe without a resonanse as it is in Fisher CZ-6...Minelab Elite etc.? can you share up TX driver's sketch?

yours

[Mrand]

This is interesting part of X-5 schematic
Mrand