Keeping the main breaker from tripping

[Alan Anderson]

Originally Posted by GeeTwo

For anyone trying to implement this --the voltage produced by the ring (which merely needs to be conductive, not ferrous) is directly related to the RATE OF CHANGE of the current....

That might be true if using an inductive sensor, but a Hall effect transducer responds to magnetic flux directly. The ring is not acting as a transformer element, but as a flux concentrator, and does need to be ferrous.

[philso]

Originally Posted by Alan Anderson

That might be true if using an inductive sensor, but a Hall effect transducer responds to magnetic flux directly. The ring is not acting as a transformer element, but as a flux concentrator, and does need to be ferrous.

We use a lot of commercially made Hall Effect current sensors at work. They all have ferrous flux concentrators. For certain applications, we get custom sensors made with special ferrous materials that work to higher frequencies than the silicon-steel they normally use.

Originally Posted by GeeTwo

For anyone trying to implement this --the voltage produced by the ring (which merely needs to be conductive, not ferrous) is directly related to the RATE OF CHANGE of the current. You will need to keep a running total of the voltage to get a good value for current draw. I don't see how you're going to keep from having significant drift in a practice session unless you pause and recalibrate regularly, though perhaps over the duration of an FRC match it wouldn't be too bad. This trick works well for A/C meters because the current is constantly changing (and adds up to zero), so that the average voltage induced over a 1/60 sec cycle is proportional to the RMS current flow. For DC, no such luck - if you draw a steady curent, whether 1A or 110A, the voltage will be zero after it stabilizes.

Change to a ferrous ring then use an oscilloscope to check the output of your homemade sensor again. You may want to compare the output of your homemade sensor against the output of a commercially available current sensor that is capable of reading DC; i.e. a current clamp probe. Depending on what you are trying to do and your accuracy requirements, you may have to calibrate your sensor against a known standard.

You may be much happier using a commercially made sensor such as the one in the link below.

http://www.digikey.com/product-detai...168-ND/4990649

LEM has put a lot of hard work into reducing the inherent drift in the offset voltage (over temperature and time) and to linearize the output. For comparison, the SS49E/SS59ET Series from Honeywell has an effective offset of +-10% at 25 C. It is likely to be worse at other temperatures. There is no spec for linearity.

Get in touch if you want help choosing a commercially made Hall Effect current sensor.

[Al Skierkiewicz]

Tom,
That is generally the case for powered connectors but in my work, the signal direction determines the male plug. That is why all microphones have male XLR connectors and mixers have female XLR sockets. For fixed installations we provide connectors of both flavors so that the direction convention can be maintained. (yes, we cheat with turn arounds when needed) Camera hardware is the same whether it was the old TV 81 cable, Triax or fiber. TV81 had some reversed pins because voltage(s) was generally sent to the camera for operation. In some cases this was pretty high. In the case of Triax, original cameras could have 220 VAC running to the camera on the inner conductors but the female connector was designed so you can't contact both of those easily. Newer designs have far less voltage feeding the camera.

[Jared]

Originally Posted by Tom Line

It prevents someone from unplugging a wire from a motor or sensor and accidentally shorting the power pin to ground. I've always assumed that's the same reason the prongs always go into your wall at home, but never verified it.

You're right. Extension cords with two male ends are sometimes called suicide cords because they're so dangerous, and they really should never be used. I've only seen two, one to plug a generator into a dryer outlet, and one that was used for stage lighting.

[Al Skierkiewicz]

Jared,
That adapter used for stage lighting is prohibited in my jurisdiction (Cook County, Il). Someone caught doing that could potentially lose their job and/or incur a large fine. In your area, I suspect older venues may get a pass if they have not upgraded their equipment. I believe the manufacturer of the plug set I am thinking of was Mole Richardson.

http://i347.photobucket.com/albums/p...g?t=1272819042