Re: [CAD_CAM_EDM_DRO] Re: panel meters

On Saturday 13 March 2004 12:54 am, Bob McKnight wrote:

> I guess the question I really have regards matching the meter
> to the transformer.
> In analog meter movements there is a rating f.s. which is full
> scale meter movement or the voltage required to swing the meter
> needle across the scale to maximum voltage.
> There is another rating which is the resistance of the meter
> movement. My memory is that I thought I had a good meter
> in the old Simpson 260? multimeter at 20,000 ohms/volt.

Yeah. I have one of those that's about as old as I am, still going strong.
:-)

> So the question is Does the resistance of the meter movement make much of a
> difference in the reading you get across the Current Transformer.

It matters, yeah.

> I always thought it did so used the old panel meters from substation
> panels to make sure I got a fairly accurate reading.

Any given meter movement is going to have a specific resistance, voltage, and
current to give a full-scale indication. Where you want a "sensitive" meter
movement is when the impedance of the measuring circuit is likely to have
some effect on what you're trying to measure, which doesn't strike me as
being too likely in this application.

What you need is to find out what voltage, etc. is going to appear on the
output side of that transformer for the maximum you want to be able to
measure, and then have an appropriate resistance in the circuit from there.
Feel free to contact me off-list if you need details, I may be able to come
up with a link or two that'll help.