Filter cap breakdown?

[Coyoteboy]

I have a circuit designed to condition a VR sensor signal, using an LM1815
conditioner, its fairly well used with different VR sensors but with one
particular setup it seems to have lots of trouble. The input to the 1815
has a low-pass filter setup including a 330pf/200v ceramic cap to earth.
Ive been noticing "false triggering" on power-up, for the first 30 seconds
or so, and mis-triggering at fairly high RPMs - im wondering if this
particular VR sensor setup produces >200v peak at high revs and has damaged
the filter cap, therefore causing a loss of noise protection at power on
and losing signal at high revs.

Any takes on this? Is that a reasonable supposition?
J

 

[Ernie]

"Coyoteboy" <coyoteboyuk@hotmail.com> wrote in message
newsP6dnfwBQ4b8VIHbRVnyjAA@bt.com...

I have a circuit designed to condition a VR sensor signal, using an LM1815
conditioner, its fairly well used with different VR sensors but with one
particular setup it seems to have lots of trouble. The input to the 1815
has a low-pass filter setup including a 330pf/200v ceramic cap to earth.
Ive been noticing "false triggering" on power-up, for the first 30 seconds
or so, and mis-triggering at fairly high RPMs - im wondering if this
particular VR sensor setup produces >200v peak at high revs and has
damaged
the filter cap, therefore causing a loss of noise protection at power on
and losing signal at high revs.

Any takes on this? Is that a reasonable supposition?
J

It seems feasable to me. Is the circuit in any way tied to the 120VAC line?
I have had 200V input filter caps fail in tube radios I was working on. I
beleive my failures were caused by spikes (and age of the capacitors as
well) since 120VAC is RMS meaning it is actually about 170V peak, very close
to the rated 200V. I had replaced mine with 600-volt caps and they've been
reliable ever since.

Ernie

 

[Coyoteboy]

Ernie proclaimed to alt.electronics ...

"Coyoteboy" <coyoteboyuk@hotmail.com> wrote in message
newsP6dnfwBQ4b8VIHbRVnyjAA@bt.com...
I have a circuit designed to condition a VR sensor signal, using an LM1815
conditioner, its fairly well used with different VR sensors but with one
particular setup it seems to have lots of trouble. The input to the 1815
has a low-pass filter setup including a 330pf/200v ceramic cap to earth.
Ive been noticing "false triggering" on power-up, for the first 30
seconds or so, and mis-triggering at fairly high RPMs - im wondering if
this particular VR sensor setup produces >200v peak at high revs and has
damaged
the filter cap, therefore causing a loss of noise protection at power on
and losing signal at high revs.

Any takes on this? Is that a reasonable supposition?
J

It seems feasable to me. Is the circuit in any way tied to the 120VAC
line?
I have had 200V input filter caps fail in tube radios I was working on. I
beleive my failures were caused by spikes (and age of the capacitors as
well) since 120VAC is RMS meaning it is actually about 170V peak, very
close
to the rated 200V. I had replaced mine with 600-volt caps and they've
been reliable ever since.

Ernie

Nope, its on a vehicle ignition system - I suppose through some strange
shorting it could get a crack of 15Kv but I'd expect that to take out other
things too lol. I've investigated the VR sensors more heavily and dont seem
to get more than 50v p-p so i dont think that is the answer. But thanks for
chewing it over with me!

--
J