The Keithley 427 is a precision feedback-type current amplifier designed for accurate measurement and amplification of low-level current signals across eight decade gain ranges from 10⁴ to 10¹¹ V/A. It delivers ±10 V output at up to 3 mA with resolution down to 10⁻¹³ A, making it ideal for applications demanding exceptional sensitivity and dynamic range.
Technical Specifications
Gain & Resolution
• Eight decade ranges: 10⁴ to 10¹¹ volts/ampere
• Resolution: 10⁻¹³ amperes to 10⁻³ amperes full output
• Output: ±10 volts at up to 3 milliamperes
• Output resistance: Less than 10 ohms DC to 30 kHz
Accuracy & Stability
• Output accuracy: ±2% of reading up to 10⁹ V/A; ±4% of reading on 10¹⁰ and 10¹¹ V/A ranges (exclusive of noise, drift, and current offset)
• Voltage drift: Less than 0.005% per °C and less than 0.005% per day after 1-hour warmup
• Offset current: Less than 10⁻¹² amperes at 25°C
Response & Noise
• Rise time (10% to 90%): Adjustable from approximately 15 µs to 330 milliseconds
• Fastest rise time: 15 µs at 10⁸ V/A gain; 1.5 ms at maximum gain of 10¹¹ V/A
• Noise at 10¹¹ V/A gain: As low as 3 × 10⁻¹⁴ A rms with 13,000:1 dynamic range at slower rise times
• Dynamic reserve: 10 (20 dB)
Input Characteristics
• Effective input resistance: Less than 15 ohms on 10⁴–10⁵ V/A ranges; less than 4 megohms on 10¹¹ V/A range
• Input voltage drop: Less than 400 µV for full-scale output when properly zeroed
• Maximum input overload (transient): 1000 volts for up to 3 seconds; (continuous): 500 volts on 10¹¹–10⁷ V/A ranges, decreasing to 20 volts on 10⁴ V/A range
• Input shunt capacitance: Maximum 1000 pF
Current Suppression
• Adjustable range: 10⁻¹⁰ to 10⁻³ amperes in eight decade ranges
• Resolution: 0.1% via 10-turn potentiometer
• Stability: ±0.2% of suppressed value per °C and ±0.2% per day
– Key Features
• Overload indication lamp for pre-filter or post-filter conditions
• Selectable rise-time steps of 1× and 3.3×
• Current offset compensation doubles per 10°C above 25°C
– Typical Applications
• Automated semiconductor testing
• Mass spectrometry
• Gas chromatography
• Ion chambers and high-impedance electrodes
• Photomultiplier tubes and phototubes
• Beam current and semiconductor property measurement
