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The Keithley 428 Current Amplifier converts fast, small currents to a voltage, which can be easily digitized or displayed by an oscilloscope, wave-form analyzer, or data acquisition system. It uses a sophisticated "feedback current" circuit to achieve both fast rise times and sub-picoamp noise. The gain of the 428 is adjustable in decade increments from 10^3 V/A to 10^11 V/A, with selectable rise times from 2 µs to 300ms. Input and output connections to the 428 are made with BNC connectors. INPUT HI is connected to a programmable ±5V supply, which permits suitable bias voltages to be applied to devices-under-test or current collectors. This eliminates the need for a separate bias supply. Specifications. Input Voltage Burden: <200 µV (18°–28°C) for inputs <100 µA; <10 mV for inputs >= 100 µA; 20 µV/°C temperature coefficient. Input Maximum Overload: 100V on 10^4 to 10^11 V/A ranges; 10 V on 10^3 V/A range. Higher voltage sources must be current limited at 10 mA. Output Range: ±10V, 1 mA; bias voltage off. Output Impedance: <100 ohm DC - 175 kHz. Low Pass Ranges: 10 µs to 300 ms (±25%) in 1, 3, 10 sequence or OFF. Output Attenuation: 12 dB/octave. Gain ×10: Rise time, noise, and input resistance are unchanged when selecting GAIN ×10; gain accuracy and temperature coefficient are degraded by 0.2% and 0.003%/°C respectively. Display: Ten character alphanumeric LED display with normal/dim/off intensity control.
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