# Designing an AC Current Measuring Device

#### KuBU

Joined Apr 8, 2007
5
hi !
i'm asked to design this device. by using a toroid (i think a Rogowski coil)
we'll make a current flow through the toroid and measure a voltage from the winding ..
something like this..

but i cant decide where to begin..
how can i realize a circuit like this?
or do i have a chance to simulate this circuit in PSPICE?
or which program does things like this?

#### Johann

Joined Nov 27, 2006
190
Hi! You can puchase a ring core from most electronics component suppliers. Look for one that is big enough so that you can easily thread insulated wire through it in the form of a winded coil. Use say, 50 turns for a start. Also, pass a single insulated wire through the hole of the ring. This is the basic construction of a CT (current transformer).
You'll now need a variable ac source (LOW VOLTAGE FOR YOUR OWN SAFETY!). This may be a "VARIAC" with mains input to it and the output connected to a small step-down transformer, say 12V, 2 amps rated.
Put an ac ammeter (0 - 5A) in series with the single wire that you put through the ring and connect the 2 ends to the 12V winding of the transformer. (POWER OFF at this stage!) Connect the free ends of the coil that you've wound to another ac ammeter (0 - 100mA AC).
See that the "variac" is adjusted to minimum position. Switch on AC supply. VERY SLOWLY, GRADUALLY INCREASE THE INPUT VOLTAGE to the step-down transformer. (By turning the knob of the "Variac").
Watch both ac meters carefully. STOP when you reach 1 amp on the first one and observe the reading of the second one. It should read 1/50 of the input current if the core is not saturated (20 mA). Never turn the "Variac" up more, because you'll exceed the step-down transformers capabilities! (Remember, it is effectively shorted out in this experiment!)