I recently picked up an old (antique?) ammeter, mainly because it looks cool, but I'm wondering if there is anything I can "do" with it.

It's a Weston model 155, and you can find a picture here: http://www.humboldt.edu/~scimus/HSTC.27-35/Descriptions/ACVMeter155.htm. In short, this is an AC ammeter, marked from 0-300A. I have a couple of questions about it.

First, how can I test this? I figured I could shunt this in to my clothes dryer circuit (15A or 30A, I forget), but then again, I might just set the house on fire if I do so.

Second, this is an AC meter, and I'm not sure of what the difference between meters. From what I can tell (from this website) is that DC meters usually have a shunt resistor, and that is what gives the rating of the meter.

Is there any way I could use this for a toy, perhaps just driving it with the PWM of an AVR microcontroller?

 

Your link describes a voltmeter. Are you sure you have an ammeter? John

 

Whoops, I must have used the wrong link. Sorry, this is the actual meter I purchased:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230246251062#ebayphotohosting

 

Is there any way I could use this for a toy, perhaps just driving it with the PWM of an AVR microcontroller?

Up to 300A? Hell of a toy!

 

I don't know, monitoring house current perhaps? Kidding of course.

 

Put it in the the dash of your Jaguar XK140 to monitor the generator? (http://en.wikipedia.org/wiki/Jaguar_XK140)

John

 

It should have a shunt to scale it. Changing the shunt will let it respond to lower currents. Think of the fun - scaling the response to 3 amps full scale, but still indicating 300.

 

I guess the better question would be: what is the difference between an AC meter movement (of any sort) versus a DC meter movement? And what makes a meter an ammeter versus a voltmeter?

For the particular meter I am asking about, I opened it up, and it looks like it's basically a huge magnet that loops around the movement; one end of the magnet starts at one of terminals, loops around the movement, and goes to the other terminal. I can take a picture if that helps.

 

It either has diodes and filtering to get a representation of the AC current or it uses coil winding techniques to do the same thing.

You can research the patent if it's on it.