Live wire sensor

[alansimpson]

Just out of idle curiosity.
How does a domestic live wire detector sense AC live wires without coming into contact, when there is no current in live wire to induce current in sensor.
The AC potential alone must generate a field that sensor detects when it is close to conductor, but how?

Thanks in advance.

 

[Skogsgurra]

Yes, you are right. There is an AC electric field that can be picked up and used by an amplifier or even directly by a CMOS gate.

We once designed a little telephone answerer that checked if there was voltage on the grid and what temperature you had in the leisure cottage. Plus a few switches.

We had a problem with the voltage supervision until we found out that a few feet of wire along any mains cord picked up enough stray voltage to activate a standard CMOS gate. Worked like a dream. And we never had to attach the box to the grid.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[danw2]

>a little telephone answerer that checked if there was voltage on the grid and what temperature you had in the leisure cottage.

Gunnar,

OK, you've stumped me.

You detect line voltage and cottage (ambient?) temperature and decide whether or not to answer a telephone. I'm not sure why anybody would want to do that, so I'm curious why and what the truth table looks like

voltage + low temp = answer or no answer
voltage + high temp =
low/no voltage + high temp =
high voltage + low temp =

Dan

 

[Skogsgurra]

This is in cold Sweden. Little houses all over the country. People go there in the summer, but not very often in the winter.

These little houses often have running water installed, some have freezers and all have windows. Many guys go to their little houses just to see if everything is OK and then back home again. Distances are sometimes 500 km (300 miles) one way and it is both time-consuming and expensive to do such an "inspection trip" so many don't do it. Only to find out that a snow storm or lightning or burglars have hit the house so that water pipes have frozen or that elk, bear, reindeer, trout or salmon meat in the freezer has gone bad.

So, we designed a little battery thing that checks if basic things like mains voltage, temperatures, windows and doors are OK. It is called "Stugvakten", which means "Cottage Guard". Battery life is around five years (three AA cells). We were contemplating marketing it in Russia. Name "Datja-Safe". But not done that yet. You phone it and it answers with simple tone codes.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

There are a lot of those about as they make good sense. Most have screw terminals on them so you can hook them to alarm systems. They also have microphones in them and if a lound noise occurs they will silently call a number. If any of the contacts close they can also call the number and play a built in message that says "alarm

"

http://www.smarthomeusa.com/ShopByManufacturer/microtechnologies/Item/VM500-2/

http://www.homesecuritystore.com/ez...extag&zmam=55691497&zmas=1&zmac=4&zmap=THP217

Keith Cress
kcress -

http://www.flaminsystems.com