Stanford Research SR865 DSP Lock-In Amplifier, 2 MHz

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Category: Amplifiers - RF and Microwave Other

Stanford Research SR865 (Available for Rent)

The SRS SR865 Lock-In Amplifier stands as a benchmark for high-performance measurement in the realm of scientific instrumentation. With value-packed features, this advanced amplifier is designed to meet the stringent demands of laboratory research and precision applications.

Lock-in performance begins at the front end with the SR865, featuring both voltage and current input amplifiers. Its voltage input is a switchable single-ended/differential JFET pair amplifier, boasting an exceptional noise level of just 2.5 nV/√Hz at 1 kHz and under 10 nV/√Hz at 10 Hz. The unit delivers a 10 MΩ input impedance and offers both AC and DC coupling options. Users can connect input connector shields to the instrument ground via a selectable 10 Ω (Ground) or 10 kΩ (Float) resistor.

The built-in current amplifier signifies a major advancement in design, supporting a selectable current input range of 1 µA and 10 nA. The 1 µA range features a bandwidth of 400 kHz with a noise level of 130 fA/√Hz, while the 10 nA option achieves a bandwidth of 2 kHz with a noise level of 13 fA/√Hz.

While the integrated voltage and current amplifiers are suitable for a majority of applications, the SR865 is compatible with a complete range of specialized pre-amplifiers from SRS, including the SR550 (FET input), SR552 (BJT input), SR554 (transformer input), SR555 (120 kHz current amp), and SR556 (low noise current amp), all powered directly from the instrument's rear-panel preamp power port.

A notable feature of the SR865 is its user-friendly sensitivity setting, which defines the voltage (or current) producing a full-scale output. Users can easily configure the input range from the front panel without delving into complicated dynamic reserve equations. This straightforward approach ensures experimental efficiency, enabling a seamless selection of sensitivity matched to the least-overload input range, simplifying the overall setup.

The effective dynamic reserve of the SR865 becomes apparent through the ratio of sensitivity settings, exemplified by a 10 nV sensitivity and a 300 mV input range yielding an exemplary dynamic reserve of 3 × 10⁷, nearly 150 dB.

A variety of traditional RC-response time constants can be selected, ranging from 1 µs to 30 ks, with roll-off options of 6, 12, 18, and 24 dB/oct. Additionally, the SR865 features advanced digital filters that enhance measurement efficiency while amplifying signal-to-noise ratios. Gaussian FIR filters are utilized for time constants below 3 s, delivering superior rise-time characteristics and stopband attenuation, preserving feature shapes even under scanning. For longer time constants, linear phase IIR filters are employed, effectively settling nearly twice as quickly as their RC counterparts.

Synchronous filtering mode is available for reference frequencies below 4 kHz, effectively eliminating multiples of reference frequencies that could interfere with low-frequency measurements. This synchronous filter operates without sacrificing output resolution, presenting a significant upgrade from previous models.

The SR865 accommodates a reference frequency range from 1 mHz to 2 MHz, allowing detection at the fundamental or up to the 99th harmonic. Users can choose from several reference modes: Internal mode utilizes the amplifier's precision internal oscillator, External mode syncs to an external sine or TTL signal, Dual Mode detects at the difference frequency, and Chop mode employs a digital PID controller for precise synchronization with an SR540 Optical Chopper, virtually eliminating frequency drift.

Furthermore, the SR865 comes with a precision sine wave output, configurable with 6 digits of frequency resolution and an amplitude range from 1 nV to 2 V. This output can be adapted as a single-ended or differential (balanced) signal, with a DC offset of ±5 V available. A rear-panel logic-level sync signal aligns with the sine output for enhanced utility.

The instrument also provides rear-panel 10 MHz inputs and outputs, enabling locking to an external frequency reference, or using the 10 MHz output for synchronizing multiple lock-ins or test equipment.

Expanding its versatility, the SR865 features a built-in FFT display, offering insights into the frequency domain to enhance signal analysis and noise tracking, showcasing various input, post-mixer, and filtered signal spectra.

The centerpiece of user interaction is a full-color 640 × 480 touchscreen, capable of displaying up to 4 channels of data. Configurations allow for the viewing of large numeric results or “strip-chart” displays, providing extensive time-tracking capabilities. All measurements are continuously recorded, ensuring that valuable data is never lost. The touchscreen allows easy access to core parameters while dedicated knobs and buttons facilitate common controls.

Computer connectivity is robust with GPIB (IEEE488.2), RS-232, USB, and Ethernet interfaces, accompanied by a webserver for remote monitoring and control through a simple browser interface. Moreover, when connected to a Wi-Fi network, the SR865 supports remote operations via an iOS app, allowing seamless access to configurations and live data from handheld devices. Data and screenshots can easily be exported via a front-panel USB port in comma delimited formats or MATLAB compatible .MAT files.