An ion beam current measurement device includes a first Faraday cup having a first ion beam entrance slit of a first width W1. The first Faraday cup is configured to generate a first current signal. The device further includes a second Faraday cup having a second ion beam entrance slit of a second width W2. The second Faraday cup is configured to generate a second current signal. The slit widths are designed such that W2 is greater than W1.