Re: Power sensor?

On Fri, 19 May 2006 20:45:11 +0100, markp <map.nospam@xxxxxxx> wrote:

"Ignoramus23298" <ignoramus23298@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:c6obg.75832$kW1.27355@xxxxxxxxxxxxxxxxxxxxxxxx
I would like to know if there are any easy options for making a power
signal, out of DC current shunt voltage (up to 50 mV) and rail to rail
voltage. (power = voltage * current)

thanks

i


Google for 'high side current measurement'. There are specific devices,
basically differential opamps with very wide common mode operating range
that exceeds the power supply, that can be used to measure current. Knowing
the high side voltage you can then calculate power.

What do you mean by "calculate power", are you referring to using a
calculator?

If so, that's not what I was looking for, I can surely use a
calculator and multimeter to multiply voltage by current, but I need
some device to make real time signal that is proportional to V*I.

Let me explain: I made a power supply. High power, 0-300 VDC, 0-200
amp, about 10 kW or so. (a welder actually).

It is controlled by SCRs and uses a controller that takes a voltage
input and "current input". The controller regulates SCR firing phase
angle to match the voltage and current.

It works. Does welding with stick already.

http://igor.chudov.com/projects/Welding/11-New-Rectifier/dscf0255.jpg

It can be made into a constant current or constant voltage source
based on potentiometer settings.

Since the controller does not know what is the current input, I could
as well use a "watt transducer" to input _power_ instead of getting
input from a _current_ shunt.

That would make a constant power welder.

For this, I need a power transducer that would perform multiplication
of I by V.

An example of such a device is here:

http://www.flex-core.com/mt-photo.htm
http://www.flex-core.com/page81.htm

I called them and they quoted $600 for it, which is beyond my means.

Are there any cheaper ways to achieve what I want (make a watt
transducer).

i

.

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