Stanford Research SR844
Experience unparalleled accuracy and performance with the Stanford Research SR844, a cutting-edge lock-in amplifier boasting wide bandwidth capabilities. Designed for precision measurements, the SR844 features an impressive frequency range of 25 kHz to 200 MHz and offers up to 80 dB of drift-free dynamic reserve, making it one of the most versatile instruments on the market.
Utilizing advanced DSP technology similar to that of the acclaimed SR850, SR830, and SR810 amplifiers, the SR844 ensures superior performance. This innovative technology provides significant advantages over traditional analog instruments, including high dynamic reserve, low zero-drift performance, accurate RF phase shifts, and orthogonality. Additionally, it includes digital output filtering for enhanced signal clarity.
The SR844 features both 50 Ω and 1 MΩ inputs, catering to diverse applications. The 1 MΩ input is ideal for high source impedances at lower frequencies or when using standard 10× scope probes, while the 50 Ω input offers optimal RF signal matching. With full-scale sensitivities ranging from 1 Vrms (+13 dBm) down to 100 nVrms (-127 dBm), and selectable RF gain or attenuation, this amplifier provides exceptional flexibility and performance.
Designed with user-friendliness in mind, the SR844 allows for both external and internal reference operation across the entire frequency range without manual range selection. The external reference input features an auto-threshold function that locks onto sine, square, or pulsed signals, while the internal reference is digitally synthesized with 3-digit frequency resolution for precise adjustments.
For harmonic detection, the 2F component is accessible in both modes, enhancing measurement accuracy. A phase synchronous reference output (1.0 Vpp square wave into 50 Ω) complements both internal and external operations, ensuring robust performance.
The SR844 supports flexible time constants ranging from 100 µs to 30 ks, with options for 6, 12, 18, or 24 dB/oct roll-off. For high-bandwidth applications, the "No Filter" mode allows near-instantaneous updates every 10 to 20 µs, with an effective time constant of around 30 µs.
Ease of use is guaranteed with a straightforward front-panel keypad for all instrument functions, complemented by a convenient parameter adjustment knob. Up to nine different instrument configurations can be stored in non-volatile memory, promoting quick and reliable setup. Connectivity is seamless with standard RS-232 and GPIB (IEEE-488.2) interfaces for integration with data acquisition systems.
Enhancing usability, auto-functions optimize frequently adjusted parameters such as sensitivity, dynamic reserve, phase, and offset through simple keystrokes. The auto-offset function is particularly useful for nulling input values, while the output expand feature increases resolution by up to 100×.
The ratio mode normalizes signals against an externally applied analog voltage, effectively minimizing source intensity fluctuations. The intuitive front panel enables users to conduct transfer function measurements through programmable scans of up to 11 frequencies, recalling setups and offsets automatically.
Two displays provide user-defined outputs for measuring X, Y, R, R(dBm), Θ, and noise levels, enhancing data interpretation. Additionally, it includes two user-programmable DACs with outputs ranging from -10.5 V to +10.5 V and a resolution of 1 mV, adjustable via front panel or computer interfaces.
Moreover, the SR844 features two 16-bit ADCs for general-purpose analog input, capable of displaying data on the front panel or transmitting via the interfaces. The dual 16,000-point memory buffers record time histories at sampling rates up to 512 samples/s, with data transferable using either interface. A trigger input ensures synchronization of data recording with external events during complex measurements.
