Maker Pro
Maker Pro

TDS 210 - worrying leakage current !

E

Eeyore

Jan 1, 1970
0
I've been struggling with this utter POS scope again (it seems determined to
trigger on any HF energy and reject LF for example) and ended up dragging my old
CRT scope along in its place.

When I got a trace on the conventional CRT scope that made sense / I could use
(long story there) I decided to see if the TDS 210 could redeem itself. I hooked
it up to the audio analyser we were using and it 'upset' things.

I detached the BNC lead between the bTDS210 and the audio meter and it calmed
down again. On attempting to re-attach it both I and my colleague saw a tiny
blue spark. Simply touching the BNC bodies together caused this.

I measured 0.15mA leakage current from the TDS210 ground to our EUT ground yet
there is apparently continuity (0.1 ohms) from the TDS210 BNCs to the mains
earth pin on the power lead. I've noticed before that it causes trouble when
hooked up to other gear btw.

Any thoughts (aside from having it checked). I noticed there was a recall on
these for an earth problem but I can't see how it relates to what we're seeing
here.

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Eeyore"
I've been struggling with this utter POS scope again (it seems determined
to
trigger on any HF energy and reject LF for example) and ended up dragging
my old
CRT scope along in its place.

When I got a trace on the conventional CRT scope that made sense / I could
use
(long story there) I decided to see if the TDS 210 could redeem itself. I
hooked
it up to the audio analyser we were using and it 'upset' things.

I detached the BNC lead between the bTDS210 and the audio meter and it
calmed
down again. On attempting to re-attach it both I and my colleague saw a
tiny
blue spark. Simply touching the BNC bodies together caused this.

I measured 0.15mA leakage current from the TDS210 ground to our EUT ground
yet
there is apparently continuity (0.1 ohms) from the TDS210 BNCs to the
mains
earth pin on the power lead. I've noticed before that it causes trouble
when
hooked up to other gear btw.

Any thoughts (aside from having it checked). I noticed there was a recall
on
these for an earth problem but I can't see how it relates to what we're
seeing
here.


** It may very well be related.

http://www.tek.com/service/safety/tds200/index.html

There was a high the risk of damage to the scope if (when, really ) the
signal ( BNC) earth was connected to a source of significant energy - ie
the AC supply, a large PSU etc. Doing this would blow open fairly light
gauge copper tracks on the analogue PCB, destroy the scope and possibly
electrocute the user.

Only the latter prompted a safety recall.

The fix was to add a length of 1.5 sq mm copper earth wire from the input
BNCs to the AC supply ground near the IEC inlet.

Depending exactly where this new ground wire was fitted, it may well pick up
HF magnetic noise from the SMPS.

Wound that explain your leakage current and misbehaving synch ??




......... Phil
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeyore"

** It may very well be related.

http://www.tek.com/service/safety/tds200/index.html

There was a high the risk of damage to the scope if (when, really ) the
signal ( BNC) earth was connected to a source of significant energy - ie
the AC supply, a large PSU etc. Doing this would blow open fairly light
gauge copper tracks on the analogue PCB, destroy the scope and possibly
electrocute the user.

Only the latter prompted a safety recall.

The fix was to add a length of 1.5 sq mm copper earth wire from the input
BNCs to the AC supply ground near the IEC inlet.

Depending exactly where this new ground wire was fitted, it may well pick up
HF magnetic noise from the SMPS.

Wound that explain your leakage current and misbehaving synch ??

That's certainly a possibility. I'll check later.

Thanks Phil.

Graham
 
S

Spehro Pefhany

Jan 1, 1970
0
I've been struggling with this utter POS scope again (it seems determined to
trigger on any HF energy and reject LF for example) and ended up dragging my old
CRT scope along in its place.

When I got a trace on the conventional CRT scope that made sense / I could use
(long story there) I decided to see if the TDS 210 could redeem itself. I hooked
it up to the audio analyser we were using and it 'upset' things.

I detached the BNC lead between the bTDS210 and the audio meter and it calmed
down again. On attempting to re-attach it both I and my colleague saw a tiny
blue spark. Simply touching the BNC bodies together caused this.

I measured 0.15mA leakage current from the TDS210 ground to our EUT ground yet
there is apparently continuity (0.1 ohms) from the TDS210 BNCs to the mains
earth pin on the power lead. I've noticed before that it causes trouble when
hooked up to other gear btw.

Any thoughts (aside from having it checked). I noticed there was a recall on
these for an earth problem but I can't see how it relates to what we're seeing
here.

Graham


Sounds like a classic ground loop. You can use the differential
voltage using the two channels (without grounds connected) right?


Best regards,
Spehro Pefhany
 
J

john jardine

Jan 1, 1970
0
Eeyore said:
I've been struggling with this utter POS scope again (it seems determined to
trigger on any HF energy and reject LF for example) and ended up dragging my old
CRT scope along in its place.

When I got a trace on the conventional CRT scope that made sense / I could use
(long story there) I decided to see if the TDS 210 could redeem itself. I hooked
it up to the audio analyser we were using and it 'upset' things.

I detached the BNC lead between the bTDS210 and the audio meter and it calmed
down again. On attempting to re-attach it both I and my colleague saw a tiny
blue spark. Simply touching the BNC bodies together caused this.

I measured 0.15mA leakage current from the TDS210 ground to our EUT ground yet
there is apparently continuity (0.1 ohms) from the TDS210 BNCs to the mains
earth pin on the power lead. I've noticed before that it causes trouble when
hooked up to other gear btw.

Any thoughts (aside from having it checked). I noticed there was a recall on
these for an earth problem but I can't see how it relates to what we're seeing
here.

Graham
Funny you should mention it.
A week ago I was noting to a customer their equipment had an earthing
problem as I was picking up the occasional 'tingle' on my forearm. From
mucho experience I know this would have been about 55Vac.
Seemed odd, as I know their kit and the massive amount of metal and earth
bonding that holds it all together.
Common factor is their TDS scope I was using.
 
M

Mike Monett

Jan 1, 1970
0
john jardine said:
Funny you should mention it.
A week ago I was noting to a customer their equipment had an earthing
problem as I was picking up the occasional 'tingle' on my forearm. From
mucho experience I know this would have been about 55Vac.
Seemed odd, as I know their kit and the massive amount of metal and earth
bonding that holds it all together.
Common factor is their TDS scope I was using.

Isn't there a filter on the ac line that has capacitors to gound from each
leg?

All my computers, and TEK and HP equipment have it. Any time I lose the
ground pin on the ac line I get that old 55V tingle.

Maybe the TDS 210 has especially large filter caps.

Regards,

Mike Monett
 
B

Ben Jackson

Jan 1, 1970
0
I've been struggling with this utter POS scope again (it seems determined to
trigger on any HF energy and reject LF for example)

Maybe this is too obvious, but many Tek scopes have that exact behavior
as a triggering option.
 
E

Eeyore

Jan 1, 1970
0
Spehro said:
Sounds like a classic ground loop.

Creating 0.15 mA ?

You can use the differential
voltage using the two channels (without grounds connected) right?

You know I'm so annoyed at it I hadn't even tried ! I'll check that out.

Graham
 
E

Eeyore

Jan 1, 1970
0
john said:
"Eeyore" wrote


Funny you should mention it.
A week ago I was noting to a customer their equipment had an earthing
problem as I was picking up the occasional 'tingle' on my forearm. From
mucho experience I know this would have been about 55Vac.
Seemed odd, as I know their kit and the massive amount of metal and earth
bonding that holds it all together.
Common factor is their TDS scope I was using.

Oh ! Interesting.

Graham
 
E

Eeyore

Jan 1, 1970
0
Mike said:
Isn't there a filter on the ac line that has capacitors to gound from each
leg?

True. There normally is in any gear with an SMPS.

All my computers, and TEK and HP equipment have it. Any time I lose the
ground pin on the ac line I get that old 55V tingle.

Maybe the TDS 210 has especially large filter caps.

But if the chassis is bonded to ground...... !! ??

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Eeyore"
Creating 0.15 mA ?


** 1.5 mV into 1 ohm = absolutely typical.

Now, say how you made that current measurement.

With a DMM or a scope.




........ Phil
 
S

Spehro Pefhany

Jan 1, 1970
0
Creating 0.15 mA ?

It could read that on an ammeter. One indication would be that the
current reading does not change proportionally when you switch range
on the meter.
You know I'm so annoyed at it I hadn't even tried ! I'll check that out.

Graham


Best regards,
Spehro Pefhany
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeyore"

** 1.5 mV into 1 ohm = absolutely typical.

Now, say how you made that current measurement.

With a DMM or a scope.

I own up It was a quick check with a Fluke 75 simply to establish that there was
something there. I stopped using the TDS at that point.

Graham
 
J

john jardine

Jan 1, 1970
0
Mike Monett said:
Isn't there a filter on the ac line that has capacitors to gound from each
leg?

All my computers, and TEK and HP equipment have it. Any time I lose the
ground pin on the ac line I get that old 55V tingle.

Maybe the TDS 210 has especially large filter caps.

Regards,

Mike Monett

Yes, a lost earth was exactly what I was thinking at the time. Customers
equipment is 110Vac operation, fed from a 240V to 55-0-55, 10kVA
transformer, the "0v" solid copper linked to mains earth. Power cabling
feeding the equipment has a 6mm^2 earth cable and a separate, earthed,
overall braided screen. (plus a 'health and safety' earth tested sticker ;).
Changed the 'scope power cable, no effect. Prob' was a side issue so didn't
pursue.
 
M

Mike Monett

Jan 1, 1970
0
Yes, a lost earth was exactly what I was thinking at the time.
Customers equipment is 110Vac operation, fed from a 240V to 55-0-55,
10kVA transformer, the "0v" solid copper linked to mains earth. Power
cabling feeding the equipment has a 6mm^2 earth cable and a separate,
earthed, overall braided screen. (plus a 'health and safety' earth
tested sticker ;). Changed the 'scope power cable, no effect. Prob'
was a side issue so didn't pursue.

Only 55VAC to earth ground? That's no fun. When I make a mistake, I want to
see a huge flash, BANG!, and lots of smoke.

Regards,

Mike Monett
 
J

john jardine

Jan 1, 1970
0
Mike Monett said:
Only 55VAC to earth ground? That's no fun. When I make a mistake, I want to
see a huge flash, BANG!, and lots of smoke.

Regards,

Mike Monett
My dad was a power station electrician. He came home one day looking a bit
'grey'. Casually mentioned he'd been thrown across a sub station room after
touching some unisolated 10kV switchgear. As a kid I didn't think much of
it, parents after all are indestructable!. But now, (older and wiser maybe)
I cringe at the thought ;).
 
M

Mike Monett

Jan 1, 1970
0
john jardine said:
My dad was a power station electrician. He came home one day looking a
bit 'grey'. Casually mentioned he'd been thrown across a sub station
room after touching some unisolated 10kV switchgear. As a kid I didn't
think much of it, parents after all are indestructable!. But now,
(older and wiser maybe) I cringe at the thought ;).

You are lucky you still had a Dad.

Come to think of it, you described a 55V-0-55V system earlier, and a
tingling feeling that you knew well.

Do you have any kids?

Regards,

Mike Monett
 
J

Jim Thompson

Jan 1, 1970
0
You are lucky you still had a Dad.

Come to think of it, you described a 55V-0-55V system earlier, and a
tingling feeling that you knew well.

Do you have any kids?

Regards,

Mike Monett

Good grief! Electric shock only gets the juices flowing. I got it
arm-to-arm one time when I was a kid... before GFCI's. A quick
thinking neighbor kicked my arm loose ;-)

...Jim Thompson
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore Fucking IDIOT TROLL "
I own up It was a quick check with a Fluke 75 simply to establish that
there was
something there.


** Use a bloody scope - you ass.



......... Phil
 
K

krw

Jan 1, 1970
0
To-Email- said:
Good grief! Electric shock only gets the juices flowing. I got it
arm-to-arm one time when I was a kid... before GFCI's. A quick
thinking neighbor kicked my arm loose ;-)

A week-and-a-half ago I got it across my chest (front to back); 300J
worth. I don't remember a thing that happened for about 10min. ;-)
 
Top