F-type devices are for applications with relatively high currents from nanoamps to milliamps or when high-speed data is required.
These devices use the I-V converter circuit, also known as a transimpedance amplifier. The input current passes through a resistor to develop a voltage according to Ohms law. An operational amplifier is used to balance the voltage with varying currents to provide a high degree of linearity across the measurement range.
The voltage output continuously tracks the current input. The bandwidth of the operational amplifier and stray capacitances attenuate very high frequencies. Low-pass filters attenuate frequencies closer to the ADC sample rate.
I type devices use a converter circuit with a capacitor as the feedback element. The output is the voltage across the capacitor. Using a capacitor to integrate suppresses noise and allows small input currents.
I type devices are good for measuring fast pules and very small currents.