romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
lotta variables there.....~RJ~
Which one is correct?
- Thread starter ptonsparky
- Start date
- Status
ptonsparky
Tom
- Occupation
- EC - retired
Gars’ degree of precision is far beyond what most of us use or have need of but, as usual, very educational.
I was aware that the position of my leads, even my hands, will change the 87s readings.
I can’t answer any questions about Gars variables, but would like to know what variables stand out that would be most significant in mine.
Russs57
Senior Member
- Location
- Miami, Florida, USA
- Occupation
- Maintenance Engineer
I'll just mention.....in case any of you guys carry a handheld two way radio.....they will really screw with your readings.
Key the mike and see what happens. Mine can operate automatic paper towel dispensers and some security doors (as if it was a remote control). I have heard cell phones cause audio problems in good stereo systems (when phone was not in use). Have not notice them interfere with electrical meters but it wouldn't surprise me.
Key the mike and see what happens. Mine can operate automatic paper towel dispensers and some security doors (as if it was a remote control). I have heard cell phones cause audio problems in good stereo systems (when phone was not in use). Have not notice them interfere with electrical meters but it wouldn't surprise me.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
191112-2137 EST
ptonsparky:
I would classify any reading on any instrument as valid. Is it valid for what you want to measure? Quite possibly no. However, if you have some idea of the characteristics of the device you are trying to measure. and of the measuring instrument, then you may be able to get useful information from the measurement.
As an example: if I take a 10 megohm scope probe, sync the scope on the AC line, and attach a 10 square inch conductive plate to the scope probe, then look at the scope trace as I move the plate around I will see a waveform approximately in phase, or 180 out, with AC line voltage, and an amplitude that varies with plate position. I want to hold the scope probe to insulate me from the plate so that I am not contributing much to the signal. At my bench where I have both phases present I can find a location where the composite capacitively coupled voltage is near zero to somewhat greater voltages associated with both phases. Amplitude is adjustable, and phase can change from in to out depending upon position.
If you have a Romex cable with hot energized, and an open EGC or neutral open, then you may be able to estimate the open location by a voltage measurement relative to ground, and some adjustable capacitor from the open wire to ground or to hot.
.
ptonsparky:
I would classify any reading on any instrument as valid. Is it valid for what you want to measure? Quite possibly no. However, if you have some idea of the characteristics of the device you are trying to measure. and of the measuring instrument, then you may be able to get useful information from the measurement.
As an example: if I take a 10 megohm scope probe, sync the scope on the AC line, and attach a 10 square inch conductive plate to the scope probe, then look at the scope trace as I move the plate around I will see a waveform approximately in phase, or 180 out, with AC line voltage, and an amplitude that varies with plate position. I want to hold the scope probe to insulate me from the plate so that I am not contributing much to the signal. At my bench where I have both phases present I can find a location where the composite capacitively coupled voltage is near zero to somewhat greater voltages associated with both phases. Amplitude is adjustable, and phase can change from in to out depending upon position.
If you have a Romex cable with hot energized, and an open EGC or neutral open, then you may be able to estimate the open location by a voltage measurement relative to ground, and some adjustable capacitor from the open wire to ground or to hot.
.
- Status