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John Fields · Guest

On Thu, 26 Jun 2008 16:56:32 -0700 (PDT), w_tom <w_tom1@usa.net>
wrote:

[quote]On Jun 26, 10:07 am, John Fields <jfie...@austininstruments.com
wrote:
You seem to think that someone who can>t be afforded whole-house
protection, for whatever reason, should shun the use of plug-in
protectors, even though they have been unequivocally proven to be
effective. Of course, there have been some failures, but that>s in
the nature of the game and buying high quality metal-housed units with
high-capacity transient voltage suppressors will go a long way toward
preventing failures.

So where is this proof? Current is coming down any or all AC wires
is still seeking earth ground.
[/quote]
---
No, it>s seeking Neutral.
---

[quote]Clamping the hot and neutral together
only means the same voltage is on both wires - still clamped to
nothing - surge still seeking earth ground.
[/quote]
---
First, read this:

http://en.wikipedia.org/wiki/Neutral_wire

Then consider this: (View in Courier)

HV>--+ +------L1
| |
| |
P||S
R||E--+---NEUT
I||C |
| | |
| | |
HV>--+ +--|---L2
|
GND

a typical US domestic mains supply with the voltage from L1 to L2
being 240V and the voltage from either phase to neutral being 120V,
NEUT being the center tap of the secondary of the transformer.

GND is the earthed connection of neutral, which is not designed to
carry current but is there in case of a problem with neutral.

Now consider the case where an ungrounded two-wire 120V appliance is
plugged into the mains:

HV>--+ +-----<<--+
| | |
| | [LOAD]
P||S |
R||E--+--<<--+
I||C |
| | |
| | |
HV>--+ +--|---L2
|
GND

Further, let>s define the load as resistive and dissipating 120 watts.

Such being the case, the load will have a resistance of:

E² 14400
R = --- = ------- = 120 ohms
P 120W

and the current in it will be:

E 120V
I = --- = ------ = 1 ampere
R 120R

Now let>s say that a lightning strike somewhere on the HV side of the
supply has caused a 1000V spike to occur across the half of the
secondary to which our appliance is connected.

All of a sudden, then, the voltage across the appliance will rise to
1000V, the current through it will rise to:

E 1000V
I = --- = ------ = 8.3 ampere
R 120R

and it>ll be forced to dissipate:

P = IE = 8.3A * 1000V = 8300 watts

Clearly, at this point the appliance is in serious trouble

The solution?

A plug-in protector interposed between the load and the mains, like
this:

HV>--+ +-----<<-----+------<<----+
| | | |
| | [PROTECTOR] [LOAD]
P||S | |
R||E--+--<<-----+------<<----+
I||C |
| | |
| | |
HV>--+ +--|---L2
|
GND

let>s say the protector is an MOV with a breakdown voltage of 150VRMS.

Normally, the MOV will appear to be an open circuit and will draw no
current, but what will happen when the lightning strikes is that when
the voltage across the MOV rises to 150 volts, it will break down and
allow current to flow through itself until such time as the mains
voltage falls below 150V, when it will once appear to be an open
circuit.

The reason for its use in the circuit is to prevent the voltage across
the appliance from rising to more than 150 volts, therefore providing
it with some modicum of protection against transients as can be seen
by considering that with 150V across the appliance it will be drawing
1.25 amperes and dissipating 187.5 watts, a far cry from 8.3 amperes
and 8300 watts.
---

[quote]That is the point of Page
42 Figure 8. The protector clamped all those wires together.
Therefore the surge was clamped to earth 8000 volts destructively via
the adjacent TV.

Clamping two wires together does not dissipate the energy. Surge
energy must be dissipated somewhere. A clamp to something connects
that surge energy to what dissipates that surge energy. Clamping the
hot and neutral wire means surge energy remains on both wires -
unclamped - still seeking earth ground.
[/quote]
---
Definitely not, as I have explained in the foregoing.

As a matter of fact, if we completely removed the earth ground from
the circuit:

HV>--+ +-----<<-----+------<<----+
| | | |
| | [PROTECTOR] [LOAD]
P||S | |
R||E-----<<-----+------<<----+
I||C
| |
| |
HV>--+ +------L2

the plug-in protector would work just as well.

You seem to have a misunderstanding of what "clamping" means in the
context of this discussion.

What it means is not allowing a voltage to exceed a particular value,
ergo "clamping" it to that level, which is exactly what plug-in
protectors do.
---

[quote]If plug-in protectors work as you have assumed, then where is this
manufacturer numeric spec that lists each type of surge and protection
from that surge?
[/quote]
---
Google "surge suppressor" without the quotes for a large number of
hits giving surge ratings. The word to look for is "Joules" and if
you don>t know what it means, go here:

http://en.wikipedia.org/wiki/Joule
---

[quote]No such spec exists because clamping to nothing does
not protect from the typically destructive surge. Clamping all wires
together means the surge was clamped to nothing, OR (Page 42 Figure
8) the adjacent TV did the clamping - 8000 volts destructively.
[/quote]
---
Again, you obviously don>t understand what "clamping" means in the
context of this discussion.
---

[quote]Its called a protector. So you *know* it protects from all types of
surges?
[/quote]
---
Within its ratings, yes.
---

[quote]With or without plug-in protectors, a properly earthed 'whole
house' protector is required
[/quote]
---
Not at all, as I explained earlier.

There>s not much doubt that "whole house" protection has its
advantages, but when it>s not available then plug-in protectors can be
used to good advantage.
---

[quote]which is why telcos don>t waste money
on plug-in protectors.
[/quote]
---
Apples and oranges.

JF

John Larkin · Guest

On Fri, 27 Jun 2008 16:29:55 -0700 (PDT), Ron Hubbard <ryon@quik.com>
wrote:

[quote]On Jun 27, 6:21 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 27 Jun 2008 06:08:39 -0700 (PDT), Ron Hubbard <r...@quik.com
wrote:

I bought a bunch of vacuum tubes from a surplus electronics store
that was going out of business, so many of them weren>t marked as to
what tubes they were-- but they were cheap. One in particular is a
large eight inch tube that has four pins at the bottom and two
connectors for electrode caps, one at the top and another one sticking
off to the side in an "L" shaped arrangement.

It>s obvious it>s a power tube of some sort, but does anybody have any
idea what kind? Diode or triode? I don>t know if it>s a tube number,
but marked at the base by the filaments is the number 35049... Any
help indentifying this tube would be appreciated.

Ron

Could be any of a number of parts. Can you post a pic?

Sigh... No; 'fraid not. For some inexplicable reason I can never keep
a scanner working for more than ywo or three days at the most, then
they go dead on me. Why, I don>t know, but I have the remains of four
scanners lying about just waiting for the garbage dump. ;-(

Ron
[/quote]
The cheapest USB digital camera I>ve seen, in a drug store, was
$12.95. And there are several good free picture hosting web sites
where you can dump stuff for everybody to see.

John

amdx · Guest

"christofire" <christofire@btinternet.com> wrote in message
news:cvSdnZfWqeKfhfvVRVnyiQA@bt.com...
[quote]"Ron Hubbard" <ryon@quik.com> wrote in message
news:1348aeba-9731-4a83-97a7-706b3f6662e3@r66g2000hsg.googlegroups.com...
On Jun 27, 4:34 pm, Tim Wescott <t...@seemywebsite.com> wrote:
Ron Hubbard wrote:
On Jun 27, 6:21 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 27 Jun 2008 06:08:39 -0700 (PDT), Ron Hubbard <r...@quik.com
wrote:

I bought a bunch of vacuum tubes from a surplus electronics store
that was going out of business, so many of them weren>t marked as to
what tubes they were-- but they were cheap. One in particular is a
large eight inch tube that has four pins at the bottom and two
connectors for electrode caps, one at the top and another one
sticking
off to the side in an "L" shaped arrangement.
It>s obvious it>s a power tube of some sort, but does anybody have
any
idea what kind? Diode or triode? I don>t know if it>s a tube number,
but marked at the base by the filaments is the number 35049... Any
help indentifying this tube would be appreciated.
Ron
Could be any of a number of parts. Can you post a pic?

Sigh... No; 'fraid not. For some inexplicable reason I can never keep
a scanner working for more than ywo or three days at the most, then
they go dead on me. Why, I don>t know, but I have the remains of four
scanners lying about just waiting for the garbage dump. ;-(

Ron

Perhaps you>re trying to shut the lid all the way when you try to scan a
tube?

I>d think you>d diagnose the problem after breaking a few tubes, but if
you have to break the scanner glass...

LOL. No, I don>t do that.... I scan only paper pages and on rare
occasions, a few photos, and within a day or two after turning pages
into .jpeg files or whatever, I usually have a dead scanner; go
figure.

So now I quit buying scanners.; it>s much cheaper that way.

Ron

You could use a digital camera, even one in a mobile 'phone, to take a
shot of the tube/valve.

What and break a camera and phone?[/quote]
Mike

christofire · Guest

"Claude Hopper" <boobooililililil@roadrunner.com> wrote in message
news:ZOmdnbb3N9RyvPvVnZ2dnUVZ_uWdnZ2d@giganews.com...

-- snippity snip ---

[quote]? ? ¥

Why did Kamikaze pilots wear helmets?
[/quote]

Probably in order to reach their drop zone without mishap (e.g. on account
of extreme turbulence).

Chris

Charlie Siegrist · Guest

On Thu, 26 Jun 2008 22:55:04 -0700, CharlesBlackstone wrote:

[quote]Well, first, I rent, so can>t make any permanent installations. Plus the
power supply may travel with me to the field and back and forth between
my motor test stand in one room and building bench in the other.

I bought very heavy copper lugs for 8 guage wire, they screw down. I
bought a split bolt splicer. I haven>t done anything yet, still thinking
things through. I>m noy sure how>d I>d insulate the splice.
[/quote]
I wouldn>t use a split-bolt for a temporary or mobile cable. Typically a
split-bolt is used with bare ground cable, at least in my experience.
When insulation is required, I>ve seen it wrapped with electrical tape.
The splice is bulky, and the insulation wrap prone to fraying and peeling
if moved around a lot.

I>d use an inline crimp connector, which may come with its own heat-
shrink tube insulation. "Burndy" is a good source for info on these
crimps. You realize you can>t use your 8ga. lugs on the 4ga. wire, I>m
sure :-)

[quote]But you raise an issue I have already been wondering about with your
question of using the spring-jaws.

When we charge batteries at the field we use a charger connected to the
car battery. That uses small spring jaws that come with most every
charger. In this and other cases where a spring jaw is used, the total
area of jaw touching battery must be very tiny, compared to the
thickness of the cable.
Is this a problem? It seems like the jaws would heat at those points,
and provide a tremendous resistance (though the distance is short,
true).
[/quote]
It>s a trade-off. Loss of conductance vs. ease of use. In the case of
mobile application, the ease of connection to the battery is of primary
concern.

w_tom · Guest

On Jun 28, 10:23 am, John Fields <jfie...@austininstruments.com>
wrote:
[quote]So where is this proof? Current is coming down any or all AC wires
is still seeking earth ground.

---
No, it>s seeking Neutral.
...
Now let>s say that a lightning strike somewhere on the HV side of the
supply has caused a 1000V spike to occur across the half of the
secondary to which our appliance is connected.

All of a sudden, then, the voltage across the appliance will rise to
1000V, the current through it will rise to:
...
Clearly, at this point the appliance is in serious trouble

The solution?

A plug-in protector interposed between the load and the mains, like
this:
...
Normally, the MOV will appear to be an open circuit and will draw no
current, but what will happen when the lightning strikes is that when
the voltage across the MOV rises to 150 volts, it will break down and
allow current to flow through itself until such time as the mains
voltage falls below 150V, when it will once appear to be an open
circuit.

The reason for its use in the circuit is to prevent the voltage across
the appliance from rising to more than 150 volts, therefore providing
it with some modicum of protection against transients as can be seen
by considering that with 150V across the appliance it will be drawing
1.25 amperes and dissipating 187.5 watts, a far cry from 8.3 amperes
and 8300 watts.
[/quote]

Which is all nice and good except that ohms resistance has near zero
relevance. As every responsible citation notes, *impedance* is the
critical factor. Whereas that neutral or ground wire via 50 feet of
romex may be less than 0.2 ohms, that same wire is maybe 120 ohms
impedance. Why? Wire is too long, too many splices, too many sharp
bends, etc.

A 100 amp surges is trivial. A trivial 100 amp surge 'clamped' by
the protector puts that protector at something less than 12,000
volts. That 12,000 volts puts all nearby TVs at risk as demonstrated
on Page 42 Figure 8. John – even 150 volts between H-N still means
all wires are at something less than 12,000 volts to earth.

Both 'top of the front page' articles in Electrical Engineering
Times discuss this in "Protecting Electrical Devices from Lightning
Transients" published 1 Oct and 8 Oct 2007:
[quote]The length of the cable increases the impedance dramatically.
[/quote]
Why does that responsible sources discuss impedance? Because surge
protection requires low *impedance* earthing which a plug-in protector
does not provide.
[quote]In many cases a protector should be bonded to a ground plane, ...
Often a ground grid is used to provide low impedance across the
ground plane. To intercept lightning, overhead grounded shield
wires can also be bonded to this ground plane. ...
Lightning is essentially a current impulse which is trying to return to earth.
... grounding here refers to the connection to the soil, which (hopefully)
will be the preferred path of lightning current.
[/quote]
Ground is what lightning seeks - earth ground. That protector must
be bonded *low-impedance* to earth ground. Not low resistance as John
Fields discuss. Low impedance which is why an earth ground for surge
protection is typically 'less than 10 feet'.

Why do responsible sources discuss sharp bends, splices, and wire
inside metallic conduit? None of these increase resistance - what
John discusses. All drastically increase impedance. *Low impedance*
(not resistance) defines effective protection.

Why do telcos do extensive construction so that every incoming wire
is only feet from earth ground AND up to 50 meters separated from
electronics? Again, resistance is irrelevant. Low impedance to earth
ground defines surge protection. Therefore wires must be shorter to
earth. High impedance (that up to 50 meter separation) further
supplements protection.

Plug-in protector clamping hot wire to neutral wire leaves that
surge energy still seeking earth ground. Why does the protector for
TV1 cause damage to the nearby TV2 – Page 42 Figure 8? TV1 was
protected because it was plugged into a surge protector? No.
Protector clamped surge energy to nothing. So surge energy was
shunted (connected) to earth destructively via TV2. It could have
been anything. But TV2 was the victim of that plug-in protector and
its unearthed surge. What kind of protection is that? A protector
that clamps surge energy to nothing.

More reasons why plug-in protectors are not effective: if a plug-in
protector was clamping surge energy into earth, then that 50 foot
ground (or neutral) wire bundled with all other wires has only induced
surges on other wires. Another reason why plug-in protectors can even
contribute to surge damage.

http://www.harvardrepeater.org/news/lightning.html
[quote]Since my disasterous strike, I>ve been campaigning vigorously to
educate amateurs that you *can* avoid damage from direct strikes.
The belief that there>s no protection from direct strike damage is
*myth*. ...
The keys to effective lightning protection are surprisingly simple,
and surprisingly less than obvious. Of course you *must* have a
single point ground system that eliminates all ground loops. And
you must present a low *impedance* path for the energy to go.
That>s most generally a low *inductance* path rather than just a
low ohm DC path.
[/quote]
John Fields discusses a low ohm DC path - resistance. But surge
protection (from every responsible source) is about a low *impedance*
path. What does a plug-in protector not have? A low *impedance*
connection to earth and numeric specs that even claim to provide that
protection.

One 'whole house' protector means protection for about $1 per
household appliance. Plug-in protectors cost 25 or 150 times more and
do not even claim to protect from the typically destructive surge. To
provide protection, wire impedance is not relevant. But every
responsible source defines protection in terms of impedance. John
Fields post is based on something irrelevant - wire resistance.

Ron Hubbard · Guest

On Jun 28, 4:37 am, Claude Hopper <boobooililili...@roadrunner.com>
wrote:
[quote]Ron Hubbard wrote:
On Jun 27, 6:21 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 27 Jun 2008 06:08:39 -0700 (PDT), Ron Hubbard <r...@quik.com
wrote:

I bought a bunch of vacuum tubes from a surplus electronics store
that was going out of business, so many of them weren>t marked as to
what tubes they were-- but they were cheap. One in particular is a
large eight inch tube that has four pins at the bottom and two
connectors for electrode caps, one at the top and another one sticking
off to the side in an "L" shaped arrangement.
It>s obvious it>s a power tube of some sort, but does anybody have any
idea what kind? Diode or triode? I don>t know if it>s a tube number,
but marked at the base by the filaments is the number 35049... Any
help indentifying this tube would be appreciated.
Ron
Could be any of a number of parts. Can you post a pic?

Sigh... No; 'fraid not. For some inexplicable reason I can never keep
a scanner working for more than ywo or three days at the most, then
they go dead on me. Why, I don>t know, but I have the remains of four
scanners lying about just waiting for the garbage dump. ;-(

Ron

You don>t need a scanner. You need a digital camera, download the jpg to
your computer and attach to email. No printer or scanner needed.

--
Claude Hopper :)

? ? ¥

Why did Kamikaze pilots wear helmets?- Hide quoted text -

- Show quoted text -
[/quote]
If all I wanted to do was to post pictures, I don>t even need a
digital camera-- I can buy a cheap disposable film camera, take my
photos, then have the developed pictures put onto a CD-- a process
that takes less than a day. But scanners serve other purposes than
just formatting pictures for the 'Net.

Ron

Guest · Posted: Sun Jun 29, 2008 4:15 am Post subject: Re: Down The Tubes?

On Jun 28, 7:15 pm, Ron Hubbard <r...@quik.com> wrote:
<snip>
[quote]
If all I wanted to do was to post pictures, I don>t even need a
digital camera-- I can buy a cheap disposable film camera, take my
photos, then have the developed pictures put onto a CD-- a process
that takes less than a day. But scanners serve other purposes than
just formatting pictures for the 'Net.

Ron
[/quote]
Disposable camera is a very expensive and time consuming way to do
that. You might find the digital camera to be far more useful than you
think. Taking something apart and want to get it back as it was?
Pictures. Some jerk hit your car and start to drive away? Camera will
stop them. Just as a joke I a snapped a pic of a 1" VTR scanner while
it was rotating 1 rev / field (3596.4 rpm) and completely froze the
motion. This is not some whiz-bang camera, just a Canon S2IS. You
should try it - I bet you>d like it.

G²

Jamie · Guest

w_tom wrote:
[quote]On Jun 28, 10:23 am, John Fields <jfie...@austininstruments.com
wrote:

So where is this proof? Current is coming down any or all AC wires
is still seeking earth ground.

---
No, it>s seeking Neutral.
...
Now let>s say that a lightning strike somewhere on the HV side of the
supply has caused a 1000V spike to occur across the half of the
secondary to which our appliance is connected.

All of a sudden, then, the voltage across the appliance will rise to
1000V, the current through it will rise to:
...
Clearly, at this point the appliance is in serious trouble

The solution?

A plug-in protector interposed between the load and the mains, like
this:
...
Normally, the MOV will appear to be an open circuit and will draw no
current, but what will happen when the lightning strikes is that when
the voltage across the MOV rises to 150 volts, it will break down and
allow current to flow through itself until such time as the mains
voltage falls below 150V, when it will once appear to be an open
circuit.

The reason for its use in the circuit is to prevent the voltage across
the appliance from rising to more than 150 volts, therefore providing
it with some modicum of protection against transients as can be seen
by considering that with 150V across the appliance it will be drawing
1.25 amperes and dissipating 187.5 watts, a far cry from 8.3 amperes
and 8300 watts.

Which is all nice and good except that ohms resistance has near zero
relevance. As every responsible citation notes, *impedance* is the
critical factor. Whereas that neutral or ground wire via 50 feet of
romex may be less than 0.2 ohms, that same wire is maybe 120 ohms
impedance. Why? Wire is too long, too many splices, too many sharp
bends, etc.

A 100 amp surges is trivial. A trivial 100 amp surge 'clamped' by
the protector puts that protector at something less than 12,000
volts. That 12,000 volts puts all nearby TVs at risk as demonstrated
on Page 42 Figure 8. John – even 150 volts between H-N still means
all wires are at something less than 12,000 volts to earth.

Both 'top of the front page' articles in Electrical Engineering
Times discuss this in "Protecting Electrical Devices from Lightning
Transients" published 1 Oct and 8 Oct 2007:

The length of the cable increases the impedance dramatically.

Why does that responsible sources discuss impedance? Because surge
protection requires low *impedance* earthing which a plug-in protector
does not provide.

In many cases a protector should be bonded to a ground plane, ...
Often a ground grid is used to provide low impedance across the
ground plane. To intercept lightning, overhead grounded shield
wires can also be bonded to this ground plane. ...
Lightning is essentially a current impulse which is trying to return to earth.
... grounding here refers to the connection to the soil, which (hopefully)
will be the preferred path of lightning current.

Ground is what lightning seeks - earth ground. That protector must
be bonded *low-impedance* to earth ground. Not low resistance as John
Fields discuss. Low impedance which is why an earth ground for surge
protection is typically 'less than 10 feet'.

Why do responsible sources discuss sharp bends, splices, and wire
inside metallic conduit? None of these increase resistance - what
John discusses. All drastically increase impedance. *Low impedance*
(not resistance) defines effective protection.

Why do telcos do extensive construction so that every incoming wire
is only feet from earth ground AND up to 50 meters separated from
electronics? Again, resistance is irrelevant. Low impedance to earth
ground defines surge protection. Therefore wires must be shorter to
earth. High impedance (that up to 50 meter separation) further
supplements protection.

Plug-in protector clamping hot wire to neutral wire leaves that
surge energy still seeking earth ground. Why does the protector for
TV1 cause damage to the nearby TV2 – Page 42 Figure 8? TV1 was
protected because it was plugged into a surge protector? No.
Protector clamped surge energy to nothing. So surge energy was
shunted (connected) to earth destructively via TV2. It could have
been anything. But TV2 was the victim of that plug-in protector and
its unearthed surge. What kind of protection is that? A protector
that clamps surge energy to nothing.

More reasons why plug-in protectors are not effective: if a plug-in
protector was clamping surge energy into earth, then that 50 foot
ground (or neutral) wire bundled with all other wires has only induced
surges on other wires. Another reason why plug-in protectors can even
contribute to surge damage.

http://www.harvardrepeater.org/news/lightning.html

Since my disasterous strike, I>ve been campaigning vigorously to
educate amateurs that you *can* avoid damage from direct strikes.
The belief that there>s no protection from direct strike damage is
*myth*. ...
The keys to effective lightning protection are surprisingly simple,
and surprisingly less than obvious. Of course you *must* have a
single point ground system that eliminates all ground loops. And
you must present a low *impedance* path for the energy to go.
That>s most generally a low *inductance* path rather than just a
low ohm DC path.

John Fields discusses a low ohm DC path - resistance. But surge
protection (from every responsible source) is about a low *impedance*
path. What does a plug-in protector not have? A low *impedance*
connection to earth and numeric specs that even claim to provide that
protection.

One 'whole house' protector means protection for about $1 per
household appliance. Plug-in protectors cost 25 or 150 times more and
do not even claim to protect from the typically destructive surge. To
provide protection, wire impedance is not relevant. But every
responsible source defines protection in terms of impedance. John
Fields post is based on something irrelevant - wire resistance.
[/quote]
More drivel..
Please get off the soap!.

How many times must you recite the chapter out of what ever book it is
you>re doing so. If I didn>t know any better, I swear you>re the author
of this book and trying to push it off on the rest of us.

I work in an industrial environment where we get hit on an average of
3 times each year from storms. It destroys a lot of stuff how ever,
there is very little in real life events where we work that supports
your theory as you have so edited.

We have equipment all over that uses MOV>s or devices like it that
does not depend on ground as part of the device protection. The ground
is simply there connected to the chassis and cabinets to protect the
user/operator. If it happens to be on a GFCI. It could trip the circuit
but in that case, the device attached still gets whacked normally.

http://webpages.charter.net/jamie_5"

Paul · Guest

On Jun 26, 1:53 am, Rene Tschaggelar <n...@none.net> wrote:
[quote]Paul wrote:

Thanks! As you said the output offset can always be corrected, but
it>s great to know that a 2mV op-amp chip such as the INA116PA can
apply DC voltages as low as a few nanovolts on the input device
without adding shunt resistors. Of course one can always add a shunt
resistor to lower the input voltage across the DUT, something I knew
about, but of course that has obvious effects of decreasing the DUT>s
effective input voltage to the op-amp.

I>m wondering if there are any op-amps or perhaps a BiFET amp circuit
that could achieve a few nanovolts across say a 200K ohm device while
consuming no more than a few microwatts. The idea is that such a
microwatt amp would have considerably less input thermoelectric
effects. Thermoelectric effects can generate a half dozen or more
microvolts on the DUT unless carefully balanced with dummy resistors.
I believe Linear Tech has some microwatt op-amps, but nothing near
25fA bias current.

Paul,
a thermoelectric effect means you get a voltage
from a temperature difference in case different
metal combinations are involved. They act as
input offset voltage, independent on the bias
current.
These thermoelectric effects are in the microvolt
per Kelvin region. and thus are only to be
considered in high DC-gain applications.

While FET Input opamps have far lower bias currents,
they don>t achieve the low input offset voltage
common to bipolar input OpAmps.

There are Fet input opAmps that get rid of the
input offset voltage by trading bandwidth against
the chopper feature.

Rene
[/quote]

Hi,

I>ll try to clarify:

I am referring to the input voltage on the *DUT* caused by the op-amp,
and therefore if the bias current through the DUT is decreased then
the offset voltage on the DUT will be less-- ohms law.

The op-amps I am working with have offsets around 0.5uV to a few uV.
Therefore thermoelectric effects should be considered. As far as I
know instrumentation op-amp appear to have to least thermoelectric
effects since both input pins go to the same polarity on both op-amps,
the + pin, but there are still thermoelectric effects since both op-
amps are not 100% identical. Other circuits such as the inverter
require dummy resistors and such to help reduce the thermoelectric
voltages on the DUT.

My interest in BiFET>s is to design a low power amp circuit with low
bias current.

Thanks,
Paul

w_tom · Guest

On Jun 28, 8:17 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
[quote]I work in an industrial environment where we get hit on an average of
3 times each year from storms. It destroys a lot of stuff how ever,
there is very little in real life events where we work that supports
your theory as you have so edited.

We have equipment all over that uses MOV>s or devices like it that
does not depend on ground as part of the device protection. The ground
is simply there connected to the chassis and cabinets to protect the
user/operator. If it happens to be on a GFCI. It could trip the circuit
but in that case, the device attached still gets whacked normally.
[/quote]
You use unearthed MOVs everywhere. You suffer damage from lightning
3 times a year. You call that protection? More likely, MOVs without
earth ground are earthing surges destructively through equipment.
Effective protection means direct strikes (25 annually atop the Empire
State Building) and no damage.

If MOVs are properly installed (with the required short connection
to single point earth ground), then damage occurs zero times every
year. Damage three times a year is unacceptably excessive. Your
industrial environment "does not depend on ground as part of the
device protection." Therefore damage is acceptable? Average
locations may suffer a serious surge once every seven years without
damage, if protectors are properly earthed.

Jamie demonstrates why the US Air Force demands:
[quote]15.1. Entering or exiting metallic power, intrusion detection,
communication antenna, and instrumentation lines must have
surge protection sized for lightning surges to reduce transient
voltages to a harmless level. Install the surge protection as
soon as practical where the conductor enters the interior of
the facility. Devices commonly used for this include metal
oxide varistors, gas tube arresters, and transzorbs.
[/quote]
Lightning damage three times a year is so unacceptable as to be
traceable to human failure. Properly installed 'whole house'
protector with a 'less than 10 foot' connection to earth is why:
http://www.tschmidt.com/writings/HomeLAN2008.htm
[quote]6.10 Secondary Lightning Protection
The key to minimizing lightning damage is bonding all services
together with a low impedance path to earth ground. All
conductors entering the building must be bonded together
and equipped with lightning protection. This minimizes
difference in potential during transient conditions.

6.10.1 Electrical
Whole house surge protector should be used to protect the
electrical system. Remember goal is to direct excessive energy
into a low impedance ground and to provide low impedance
bonding of all metallic conductors. ...
Lightning protectors do not absorb energy they divert it. If the
diversion path is not low impedance a substantial voltage
difference is created. This is what kills electronic gear.
[/quote]
Routine is a building connected to overhead wires all over town to
suffer maybe 100 surges during every storm and no damage. A protector
is only as effective as its earth ground. Jamie>s protectors are not
earthed. Therefore surge damage is acceptable?

steve · Guest

On Jun 26, 7:56 pm, "Tom Biasi" <tombiasi...@optonline.net> wrote:
[quote]"steve" <kvst...@gmail.com> wrote in message

news:03b46771-e8ad-45bf-8bf9-7fdf483a12cf@v26g2000prm.googlegroups.com...

Since the 9v battery supply is quickly used up, I am using a ac
battery eliminator/wall wart to run the Led timer.

Although the eliminator provides the needed 12v to 15 v, it also
changes the 50 hz dramatically to several khz.

The khz output from the eliminator completely upsets the 555 timer
input, so there is no timing available from with the circuit.

I tried a 1000uF with several diodes placed at the eliminator’s
output, but there is hardly any production of dc.

Thanks.

Steve.

Sounds like you are using a switching supply.
The wall wart is not filtered very well.
Also your project didn>t address noise on the DC supply.
I would suggest non-switching wall wart and clean up the output.
I would also look into your design since it wasn>t expecting noise from a
battery.

Tom
[/quote]
-----------------------------------------------------------------
This project was difficult to design, so preferably it should be kept
same.

I will provide the schematic shortly.

Steve.

ånønÿmøu§ · Guest

On Fri, 2 May 2008 19:54:11 +1000, "David L. Jones"
<altzone@gmail.com> wrote:

[quote]
"Dave.H" <the1930s@googlemail.com> wrote in message
news:9d258a2d-a0da-4809-af3b-98a947ece05d@k1g2000prb.googlegroups.com...
I was looking at a 12 volt regulated power supply at Dick Smith
Electronics cat. number M9935 @ www.dse.com.au for a regen radio I>m
planning on building (http://www.schmarder.com/radios/tube/
1-12af6.htm) but the AU$24 is a bit too high for my liking. I was
thinking of using a center tapped transformer, 6.3-0-6.3V @ 500mA, in
series with a 1.3 watt zener diode, I need help with obtaining 12.6
volts from a center tapped transformer, I never had to do it before.
I thought that the two positive primary leads were connected, I don>t
want to blow the transformer if this isn>t the case.

Any help appreciated,

Thanks
Dave

Transformer is M2853, and zener diode is Z3543 @ www.dse.com.au

How about $7, delivered to your door:
http://cgi.ebay.com.au/Switching-Power-Supply-12V-1A-for-CCTV-camera-AU-P24_W0QQitemZ370046177343QQihZ024QQcategoryZ20589QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Dave.

Simply brilliant and only $7 AD. w/postage.[/quote]

I may get one just to see what is inside.
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ånønÿmøu§ · Guest

On Thu, 15 May 2008 06:51:29 -0700 (PDT), Kasterborus
<kasterborus@yahoo.com> wrote:

[quote]OK,

Here>s the spec of what I>m looking at:

http://www.kako.com/neta/2007-001/circuit1.png
If you go with the four pin part you can dump the 74ac04, the 1M[/quote]
resistor, the Xtal and the two 15pf caps.

Just add power and ground and send the output to pin7 of the ir drive.
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