TAMURA open loop current sensors are available with an aperture suitable for cable and/or bus bar type primary conductors. The aperture also allows the addition of multiple primary turns or amp-turns (At) to be wound through the current sensor. This allows for improved measurement of lower primary current. Therefore a 1A X 100 Turns = 100A-Turns; 25A X 4 Turns = 100A-Turns; and 100A x 1 Turn = 100A-Turns. Considering a current sensor with a 100A rated current by winding additional primary turns the current sensor output for 1A increases from 40mV to 4V and for 25A from 1V to 4V with the indicated ampere-turns.