🚀 go-pugleaf

SteveG4685 wrote:
>
> 7-14-96
>
> Hello,
>
> How does an amp clamp meter work?
>
> More to my question should be:
> What is the best way to measure ccurrent?
>
> 120 Volts at 15 amps. max
>
> Thank for any logical ways to do it.
>
> Steve Gordon
> "amp clamp"- assume you are refering to a clamp on ammeter.
these are just current transformers that have a "split" magnetic core
that you open to place around the wire.
The current transformer secondary is usually an integral part of
a hand held meter.  To read current you just clamp the tongs (jaws)
around -one- of the wires (not both, or the net current is zero).
By both wires I am refering to "hot" and return.  Just clamp around
the "hot" wire for example.

This method of measuring is fine for most things, probably not quite as
accurate as other???

Other methods require you to break the wire and insert the meter leads.
This is not very safe for the untrained.

>How does an amp clamp meter work?

For AC is a form of transformer. A coil is wound round the halves of a
split toroidal core, and connected across a low value resistor. The
core halves are closed around the conductor, which constitutes the
(one turn) primary. The voltage across the resistor is proportional to
the current in the conductor. For DC, the actual magnetic field in the
core is measured - some devices uses hall sensors, others use clever
saturation detection techniques.

>More to my question should be:
>What is the best way to measure ccurrent?

>120 Volts at 15 amps. max

If AC, the current transformer should work fine. You can buy them or
wind them yourself on a toroidal core (tape,not ferrite for low
frequency). Warning, _don't_ run a CT with secondary opencircuited -
dangerously high voltages can be generated. A typical CT will have a
max rating of 5 va - if a 50:1, it will generate 15/50 amps (0.3A)
with 15 amps on the primary. Max voltage across the resistor would
then be 5 / 0.3 or a bit over 10 volts. In practice, 1 or 2 volts
would suffice. For 1 volt at 0.3A your resistor would be 3.33 ohms.

For more sensitivity, you can loop the onductor through the toroid
more than once, giving a proportional improvement in sensitivity.

>Thank for any logical ways to do it.

>Steve Gordon
>