How can I inspect AC mains signal on my +/-5v scope?

[Kasterborus]

I need to find a way to couple the AC mains signal to my low voltage
scope input. I'm adjusting a rotary spark gap and need to get the
"bangs" on the up and downswing of the AC cycle.

Is there something I can build with a transformer / optoisolator - or
is it easier than that?

Dave

 

[Jamie]

I need to find a way to couple the AC mains signal to my low voltage
scope input. I'm adjusting a rotary spark gap and need to get the
"bangs" on the up and downswing of the AC cycle.

Is there something I can build with a transformer / optoisolator - or
is it easier than that?

Dave

They call it a 100:1 or 1000:1 scope probe for HV work.

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

 

[Michael Black]

They call it a 100:1 or 1000:1 scope probe for HV work.

HV Probes are for actual High Voltage.

His problem isn't high voltage, but trying to connect the scope
input across the AC line. The little problem of grounding one
side of the line with the ground lead is one issue here.

He needs isolation.

Michael

 

[neon]

amazingly the probe is a has fantastic device biult into it is called i believe an attenuator. just get some resistors and build one i think it requires [2] two. You have a scope and you don't know that?WOW

 

[Phil Allison]

"Michael Black"

HV Probes are for actual High Voltage.

** Which is just what the AC supply voltage is.

His problem isn't high voltage, but trying to connect the scope
input across the AC line.

** The OP's problem IS that the AC line voltage is beyond the range of his
scope.

The little problem of grounding one
side of the line with the ground lead is one issue here.

** What need is there for that ?

The OP can use a 100:1 probe and attach the tip to the hot (or active) side
of the supply - presuming the scope ground is already linked to safety
ground.

He needs isolation.

** Nonsense.



...... Phil

 

[Phil Allison]

"John Larkin"

An AC wall-wart transformer will work, and is safe. It will introduce
just a little phase shift.

** With no load applied, an AC output "wall-wart" tranny shows no phase
error on the secondary at or near the AC voltage peaks.

However, the magnetising current value peaks around each zero crossing
causing the effective applied primary voltage to drop below the incoming AC
supply voltage at those times and hence causes the secondary voltage to
cross zero a little early - typically by about 10 degrees.

A small toroidal AC supply transformer would give the most accurate result,
cos of the very low Imag value these have.



.... Phil