Using Ct sensor instead of flux gate for measuring the 30 mA AC and 6 mA DC

Thread Starter

Ahmet Pehlivan

Joined Oct 16, 2022
I couldn't understand the electrical difference beetwen ct and flux gate so if they can measure 6 mA dc with flux gate in this reference design i though it can be also measureble with ct sensor


Joined Jan 27, 2019
A current transformer is a small, specialized transformer with the wire passing though it as the primary and the sensor itself as the secondary. A transformer cannot pass DC. There will be a small spike when the current is switched on or off, but otherwise there will be no signal to measure.

A current transformer relies on the induction that occurs when it is exposed to the changing magnetic field provided by AC. Passive sensors for DC current flow use the constant magnetic field that is generated by current flowing through the wire.


Joined Jan 27, 2019
also i don't want to measure the dc current. I want to measure dc current change (i mean 0mA to 6mA) sorry for wrong information
In this case, there is no difference. While in principle you could use the voltage spike when the current is turned on and off, it would require managing state to know what the spike means, and is really inappropriate. A simple Hall Effect sensor would provide reliable indication without the overhead.


Joined Mar 14, 2008
I want to measure dc current change (i mean 0mA to 6mA)
As noted, you can't measure DC with a CT.
You could measure a voltage from the CT due to any change in the DC current, but as soon as the change stops, the CT output goes back to zero.
So you would know the change in current, but not its steady-state value.

schmitt trigger

Joined Jul 12, 2010
Flux gate sensors operate completely differently to either CTs or Hall effect devices.
For starters, the flux gate requires a drive coil in addition to the sensing coil and the current being measured.
The flux gate also requires a saturated core design to properly check the current unbalance of a pair of conductors, which would be the leakage current.
This allows sensing small current differences from a very large current.

Use the correct sensor for the applications.