AC Current Transformer

Precise waveform measurement of long pulses

and macropulses up to several milliseconds

with minimal droop and noise




< 3Hz to 3MHz


< 1.5 µArms



The ACCT is an evolution of the active transformer first proposed by Hereward in 1960. Compared to the Hereward transformer, the ACCT presents much lower noise, a DC offset of the output reduced to a very small value and excellent long-term stability. The sensor is built with a single winding, which requires only one wire pair between sensor and electronics; this allows much better EMI rejection when long cables are used. The electronics circuit is multistage, implementing the best low-noise operational amplifier available for this application.


Two packaging type for the ACCT sensor

In-flange ACCT is mounted in the beam line. Short axial length, includes a ceramic gap vacuum-brazed to kovar. 

Does not require bellows, wall current bypass nor electromagnetic shield.

Available from CF3“3/8 to CF8“
Bakeable up to 185°C
UHV compatible

In-air ACCT installation, over the vacuum chamber Requires installation of a “gap” to prevent the wall current from flowing through the ACCT aperture.

The gap can be a brazed ceramic ring or an organic material O-ring depending on the vacuum requirements.

Typical installations include bellows, a wall current bypass and an electromagnetic shield enclosing the ACCT completely.


Two versions of ACCT electronics


ACCT electronics with 3-selectable ranges

In addition, 3 outputs available: 50Ω, 1MΩ and differential outputs

DIN-rail mountable

Power supply available




ACCT electronics with single range

Output to be read in high impedance device

DIN-rail mountable

Power supply available







Zoom Lebron XV 15



Full scale range  From 

Output full scale


Noise at 10mA FS   

Noise at 100mA FS

±1mA to ±2A


3Hz to 1MHz (3MHz on option)