For a safe circuit, add a current transformer (could just be a toroid mains transformer). Then add a resistor on the high turns ratio winding to generate a voltage when the load is on
Rectify this voltage, add cap and you have a DC voltage when the load is on
On Wednesday, December 26, 2018 at 9:40:47 PM UTC+11, snipped-for-privacy@gmail.com wr ote:
wo or three wire mains cable by detecting whenever its 240V ac load is swit ched on.
circuit after exposing the conductors please?
My guess would be that you would have to separate the live and neutral wire s by enough to let you sense the current flowing in through the live wire a nd back through neutral wire.
In the space between the live and neutral wire you'd have an alternating ma gnetic field that you could sense with a Hall sensor.
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With this device you'd just get a (small) 50Hz voltage proportional to AC c urrent through the wire, so you have to detect and rectify that and use it to generate your DC pulse. You'd have to find you own power supply to power the sensor and whatever did the signal processing.
It wouldn't be all that simple, but it would work.
Don't know how much you know about 'tronix, you can do that with an old (I did) tape recorder playback head next to the power cable. Add an opamp to amplify the picked up AC, and rectify it with a diode (use a dual opamp diode precision rectifier). Then AC coupling and a one shot to make one pulse. Power from a 9 V battery... lipo, wall wart, RTG, handcrank, ??
Position of the playback head relative to teh 3 wire cable needs some attention (you want to be close to ONE a current carrying wire).
Nope, as you can see from the picture, and in that setup I used it to measure current draw from a normal 2 wire mains lead, output to ADC. Used for years.
The trick comes from adjusting amplifiers for tape heads in film studio perfotape machines, You could perhaps also use it to listen in on POTS telephone lines without making physical contact, Playback heads have a nice pointed sensitivity range
Sounds like these heads could make good improvised current probes for oscilloscopes. It took me ages to find a decent Tektronix 'scope current probe and I had to pay through the nose for it, too. For larger currents, though, I got some of these and they work - surprisingly - really well!
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If the power wires aren't shielded, like in a conduit, an electrostatic pickup is fine. Wrap an insulated wire around the power conductors. Some oscilloscopes do that to pick off the line trigger.
I have seen an instrument that clamped the hot/black wire against a PC board to get the line trigger without making a direct line connection.
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But if the OP wants to sense a load, he needs to measure current, so needs a magnetic pickup.
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John Larkin Highland Technology, Inc trk
jlarkin att highlandtechnology dott com
You missed the point, Panteltje used a audio tape recorder head to sense current through a wire, he then amplified the signal. I believe he also said he just ran the unseparated pair (white wire pair) near the head and because the head response area is quite small it responds to the closest wire without any problem from the second wire. As he explained it, "a nice pointed sensitivity range" Probably should start saving audio heads, I think they're use may be dwindling. Mikek
On a sunny day (Wed, 26 Dec 2018 22:26:37 -0000 (UTC)) it happened Cursitor Doom wrote in :
Good price! is it not simpler to show the link as:
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then nobody has to be scared of alien website redirects.
the /itm/xxxxx where xxx is the item number.
As to the playback head, yes, but remember the induced voltage goes up with frequency etc. You will likely need some correction (like in a tape playback amplifier) I think I played with that,
We used a signal generator with a single wire in front of the head to calibrate the playback amplifier frequency correction for the perfotapes. Had to be done every now and then. Sixties.
The reason the wire is glued in position is, think of the width of a stereo head track, fraction of a cassette tape width.
I do not have all those expensive things or antiques like some here, technology had advanced, yes I used Avo in the past, but never longed back. Well I still have my old Trio analog scope from the seventies, it still works.
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