|Lock-In Amplifier||SR810 & SR830 ... from $4150|
|SR810 and SR830 — 100 kHz DSP lock-in amplifier|
|(Click to enlarge)|
|SR810 and SR830 Lock-In Amplifiers
|The SR810 Lock-In Amplifier and SR830 Lock-In Amplifier provide
high performance at a reasonable cost. The SR830 simultaneously
displays the magnitude and phase of a signal, while the SR810 displays
Both instruments use digital signal processing (DSP) to replace the demodulators, output filters, and amplifiers found in conventional lock-ins.
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SR810 User's Manual
SR830 User's Manual
SR810 and SR830 Lock-In Amplifiers
The SR810 Lock-In Amplifier and SR830 Lock-In Amplifier provide high performance at a reasonable cost. The SR830 simultaneously displays the magnitude and phase of a signal, while the SR810 displays magnitude only. Both instruments use digital signal processing (DSP) to replace the demodulators, output filters, and amplifiers found in conventional lock-ins. The SR810 and SR830 provide uncompromised performance with an operating range of 1 mHz to 102 kHz and 100 dB of drift-free dynamic reserve.
The SR810 and SR830 Lock-In Amplifiers have differential inputs with 6 nV/√Hz input noise. The input impedance is 10 MΩ, and minimum full-scale input voltage sensitivity is 2 nV. The input can also be configured for current measurements with selectable current gains of 106 and 108 V/A. A line filter (50 Hz or 60 Hz) and a 2× line filter (100 Hz or 120 Hz) are provided to eliminate line related interference. However, unlike conventional lock-in amplifiers, no tracking band-pass filter is needed at the input. This filter is used by conventional lock-ins to increase dynamic reserve. Unfortunately, band pass filters also introduce noise, amplitude and phase error, and drift. The DSP based design of these lock-ins has such inherently large dynamic reserve that no tracking band-pass filter is needed.
Extended Dynamic Reserve
The dynamic reserve of a lock-in amplifier at a given full-scale input voltage is the ratio (in dB) of the largest interfering signal to the full-scale input voltage. The largest interfering signal is defined as the amplitude of the largest signal at any frequency that can be applied to the input before the lock-in cannot measure a signal with its specified accuracy.
Conventional lock-in amplifiers use an analog demodulator to mix an input signal with a reference signal. Dynamic reserve is limited to about 60 dB, and these instruments suffer from poor stability, output drift, and excessive gain and phase error. Demodulation in the SR810 Lock-In Amplifier and SR830 Lock-In Amplifier is accomplished by sampling the input signal with a high-precision A/D converter, and multiplying the digitized input by a synthesized reference signal. This digital demodulation technique results in more than 100 dB of true dynamic reserve (no prefiltering) and is free of the errors associated with analog instruments.
The digital signal processor also handles the task of output filtering, allowing time constants from 10 µsec to 30,000 s, with a choice of 6, 12, 18 and 24 dB/oct rolloff. For low frequency measurements (below 200 Hz), synchronous filters can be engaged to notch out multiples of the reference frequency. Since the harmonics of the reference have been eliminated (notably 2F), effective output filtering can be achieved with much shorter time constants.
Digital Phase Shifting
Analog phase shifting circuits have also been replaced with a DSP calculation. Phase is measured with 0.01° resolution, and the X and Y outputs are orthogonal to 0.001°.
The built-in direct digital synthesis (DDS) source generates a very low distortion (-80 dBc) reference signal. Single frequency sine waves can be generated from 1 mHz to 102 kHz with 4½ digits of resolution. Both frequency and amplitude can be set from the front panel or from a computer. When using an external reference, the synthesized source is phase locked to the reference signal.
Auto-functions allow parameters that are frequently adjusted to automatically be set by the instrument. Gain, phase, offset and dynamic reserve are each quickly optimized with a single key press. The offset and expand features are useful when examining small fluctuations in a measurement. The input signal is quickly nulled with the auto-offset function, and resolution is increased by expanding around the relative value by up to 100×. Harmonic detection is no longer limited to only the 2F component. Any harmonic (2F, 3F, ... nF) up to 102 kHz can now be measured without changing the reference frequency.
Analog Inputs and Outputs
Both instruments have a user-defined output for measuring X, R, X-noise, Aux1, Aux 2, or the ratio of the input signal to an external voltage. The SR830 has a second, user-defined output that measures Y, Θ, Y-noise, Aux 3, Aux 4 or ratio. The SR810 and SR830 both have X and Y analog outputs (rear panel) that are updated at 256 kHz. Four auxiliary inputs (16-bit ADCs) are provided for general purpose uselike normalizing the input to source intensity fluctuations. Four programmable outputs (16-bit DACs) provide voltages from -10.5 V to +10.5 V and are settable via the front panel or computer interfaces.
The SR810 Lock-In has an 8,000 point memory buffer for recording the time history of a measurement at rates up to 512 samples/s. The SR830 has two 16,000 point buffers to simultaneously record two measurements. Data is transferred from the buffers using the computer interfaces. A trigger input is also provided to externally synchronize data recording.
The SR810 Lock-In Amplifier and SR830 Lock-In Amplifier are simple to use. All instrument functions are set from the front-panel keypad, and a spin knob is provided to quickly adjust parameters. Up to nine different instrument configurations can be stored in non-volatile RAM for fast and easy instrument setup. Standard RS-232 and GPIB (IEEE-488.2) interfaces allow communication with computers. All functions can be controlled and read through the interfaces.
|SR810 and SR830 Lock-In Amplifiers|
|Voltage inputs||Single-ended or differential|
|Sensitivity||2 nV to 1 V|
|Current input||106 or 108 V/A|
|Voltage input||10 MΩ + 25 pF, AC or DC coupled|
|Current input||1 kΩ to virtual ground|
|Gain accuracy||±1 % (±0.2 % typ.)|
|Noise||6 nV/√Hz at 1 kHz
0.13 pA/√Hz at 1 kHz (106 V/A)
0.013 pA/√Hz at 100 Hz (108 V/A)
|Line filters||50/60 Hz and 100/120 Hz (Q=4)|
|CMRR||100 dB at 10 kHz, decreasing by 6 dB/oct above 10 kHz|
|Dynamic reserve||>100 dB (without prefilters)|
|Frequency range||0.001 Hz to 102.4 kHz|
|Reference input||TTL or sine (400 mVpp min.)|
|Input impedance||1 MΩ, 25 pF|
|Phase resolution||0.01° front panel, 0.008° through computer interfaces|
|Absolute phase error||<1°|
|Relative phase error||<0.001°|
|Orthogonality||90° ± 0.001°|
|Int. reference||Synthesized, <0.0001° rms at 1 kHz|
|Ext. reference||0.005° rms at 1 kHz, 100 ms, 12 dB/oct|
|Phase drift||<0.01°/°C below 10 kHz,
<0.1°/°C, 10 kHz to 100 kHz
|Harmonic detection||2F, 3F, ... nF to 102 kHz (n < 19,999)|
|Acquisition time||(2 cycles + 5 ms) or 40 ms, whichever is greater|
|Stability||Digital outputs and display: no drift. Analog outputs: <5 ppm/°C for all dynamic reserve settings.|
|Harmonic rejection||-90 dB|
|Time constants||10 µs to 30 ks (6, 12, 18, 24 dB/oct rolloff). Synchronous filters available below 200 Hz.|
|Range||1 mHz to 102 kHz|
|Accuracy||25 ppm + 30 µHz|
|Frequency resolution||4½ digits or 0.1 mHz, whichever is greater|
|Distortion||-80 dBc (f <10 kHz), -70 dBc (f >10 kHz) @ 1 Vrms amplitude|
|Amplitude||0.004 to 5 Vrms into 10 kΩ (2 mV resolution), 50 Ω output impedance, 50 mA maximum current into 50 Ω|
|Amplitude accuracy||1 %|
|Amplitude stability||50 ppm/°C|
|Outputs||Sine, TTL (When using an external reference, both outputs are phase locked to the external reference.)|
|Channel||4½-digit LED display with 40-segment LED bar graph. X, R, X-noise, Aux 1 or Aux 2. The display can also be any of these quantities divided by Aux 1 or Aux 2.|
|Channel 2 (SR830)||4½-digit LED display with 40-segment LED bar graph. Y, Θ, Y-noise, Aux 3 or Aux 4. The display can also be any of these quantities divided by Aux 3 or Aux 4.|
|Offset||X, Y, R can be offset up to ±105 % of full scale.|
|Expand||X, Y, R can be expanded by 10× or 100×.|
|Reference||4½-digit LED display|
|Inputs and Outputs|
|CH1 output||±10 V output of X, R, X-noise, Aux 1 or Aux 2. Updated at 512 Hz.|
|CH2 output (SR830)||±10 V output of Y, Θ, Y-noise, Aux 3 or Aux 4. Updated at 512 Hz.|
|X, Y outputs||In-phase and quadrature components|
|(rear panel)||(±10 V), updated at 256 kHz|
|Aux. A/D inputs||4 BNC inputs, ±10 V, 1 mV resolution, sampled at 512 Hz|
|Aux. D/A outputs||4 BNC outputs, ±10 V, 1 mV resolution|
|Sine Out||Internal oscillator analog output|
|TTL Out||Internal oscillator TTL output|
|Data buffer||The SR810 has an 8k point buffer. The SR830 has two 16k point buffers. Data is recorded at rates to 512 Hz and read through the computer interfaces.|
|Trigger In (TTL)||Trigger synchronizes data recording|
|Remote pre-amp||Provides power to the optional SR550, SR552 and SR554 preamplifiers|
|Interfaces||IEEE-488.2 and RS-232 interfaces standard. All instrument functions can be controlled and read through IEEE-488.2 or RS-232 interfaces.|
|Power||40 W, 100/120/220/240 VAC, 50/60 Hz|
|Dimensions||17" × 5.25" × 19.5" (WHL)|
|Warranty||One year parts and labor on defects in materials and workmanship|