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Building an Ammeter with TORQUE!

Hi ..... I need help in building what is basically an ammeter with TORQUE!!!!

The current from each phase of the household current has to be summed, averaged and displayed through a pointer that rotates through 75 degrees. The device shall take the output of three current transformers, find the average and create an output that shall drive a servo motor between zero degrees and 75 degrees. When the current being drawn is zero, the rotor position shall be at zero degrees and when the current is max (as set by user), the rotor shall be at 75 degrees. Any intermediate voltage should correspond to an intermediate degree position. There should be an option to set the maximum possible current drawn. There should be a potentiometer to control the current at which the rotor moves out of the zero degree position. There should also be a test circuit that enables checking of the movement of the rotor by simulating 0-max input. All parts should be rugged and durable ... able to work continuously day in and day out. I need a total solution... a board to which I connect the leads from the three current transformers and a servo motor spindle at the other end to which I connect my pointer. I am a hobbyist with a limited budget. Hope that someone on this board can assist. Regards Skk

Reply to
skk
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IIWY I would consider something like PIC with enough ADCs and stepper motor from those old 5.24" floppy drives.

Some of those steppers had a small metalic arm on the axis that allows you to mount IR sensor(from the same drive that you scavenged stepper). With a bit of rework, you can use the same arm as an optical pointer and to sense "position 0".

The rest should be easy enough. You sample the three phase inputs, calculate average and rotate the stepper accordingly...

Regards

Branko

Reply to
BRANE-NEWS

This is not a bit of help it's a major design project and there is insufficient information to even start. You need more specification like what operating voltage, what current range is it supposed to work for. There are three different jobs here, monitoring the current, limiting the current and building a simulation rig that pretends to be the current.

Limited budget means lots of time. Commercially I would think a prototype device capable of controlling current at around the 100ma level to the rough spec you have given would cost (as a very rough guess) about £3000 as a prototype. Thats one of the three jobs, total guesstimate, £10,000.

I don't think this one is going anywhere :)

Reply to
Mjolinor

Some of these devices have RS232 outputs that (perhaps with further processing) be used to drive the servo.

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Reply to
CWatters

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