Atec SR810, SR830 User Manual

Digital Lock-In Amplifiers
SR810 and SR830 — DSP lock-in amplifiers
SR830 DSP Lock-In Amplifier
· 1 mHz to 102.4 kHz frequency range
· >100 dB dynamic reserve
· 5 ppm/°C stability
· 0.01 degree phase resolution
· Time constants from 10 µs to 30 ks (up to 24 dB/oct rolloff)
·
Auto-gain, -phase, -reserve and -offset
· Synthesized reference source
· GPIB and RS-232 interfaces
· SR810 ... $3850 (U.S. list)
· SR830 ... $4750 (U.S. list)
SR810 & SR830 DSP Lock-In Amplifiers
The SR810 and SR830 DSP Lock-In Amplifiers provide high performance at a reasonable cost. The SR830 simultaneously displays the magnitude and phase of a signal, while the SR810 displays the 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.
Input Channel
The SR810 and SR830 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 inputs 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 lock­ins to increase dynamic reserve. Unfortunately, band pass filters also introduce noise, amplitude and phase error, and drift. The DSP design of these lock-ins has such inherently large dynamic reserve that no band pass filter is needed.
Extended Dynamic Reserve
The dynamic reserve of a lock-in amplifier, at a given full­scale input voltage, is the ratio (in dB) of the largest interfering
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phone: (408)744-9040
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SR810 and SR830 DSP Lock-In Amplifiers
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 and SR830 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.
Digital Filtering
The digital signal processor also handles the task of output filtering, allowing time constants from 10 µs 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°.
Frequency Synthesizer
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.
Useful Features
Auto-functions allow parameters that are frequently adjusted to automatically be set by the instrument. Gain, phase, offset and dynamic reserve are 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 isn’t limited to 2F — any harmonic (2F, 3F, ... nF) up to 102 kHz can be measured.
Analog Inputs and Outputs
Both instruments have a user-defined output for measuring X, R, X-noise, Aux 1, 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. ADCs) are provided for general purpose use — like 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.
Internal Memory
The SR810 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, 16k 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.
Easy Operation
The SR810 and SR830 are simple to use. All 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.
Four auxiliary inputs (16-bit
Ordering Information
SR830 DSP dual phase lock-in $4750 amplifier (w/ rack mount) SR810 DSP single phase lock-in $3850 amplifier (w/ rack mount) SR550 Voltage preamplifier $750
(100 MΩ, 3.6 nV/√Hz)
SR552 Voltage preamplifier $750
(100 kΩ, 1.4 nV/√Hz)
SR554 Transformer preamplifier $1200
(0.091 nV/√Hz)
SR555 Current preamplifier $1095 SR556 Current preamplifier $1095 SR540 Optical chopper $1195
SR810 DSP Single Phase Lock-In Amplifier
Stanford Research Systems
SR810/830 rear panel
phone: (408)744-9040
www.thinkSRS.com
SR810 and SR830 Specifications
Signal Channel
Voltage inputs Single-ended or differential Sensitivity 2 nV to 1 V Current input 106 or 108 V/A Input impedance Voltage 10 MΩ + 25 pF, AC or DC coupled Current 1 kΩ to virtual ground Gain accuracy ±1 % (±0.2 % typ.) Noise (typ.) 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 to 10 kHz, decreasing by 6 dB/oct above 10 kHz Dynamic reserve >100 dB (without prefilters) Stability <5 ppm/°C
Reference Channel
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° Phase noise Internal ref. Synthesized, <0.0001° rms at 1 kHz External ref. 0.005° rms at 1 kHz (100 ms time constant, 12 dB/oct) Phase drift <0.01°/°C below 10 kHz, <0.1°/°C above 10 kHz
Harmonic detection
Acquisition time (2 cycles + 5 ms) or 40 ms, whichever is larger
Demodulator
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.
Internal Oscillator
Range 1 mHz to 102 kHz Frequency 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
2F, 3F, ... nF to 102 kHz (n < 19,999)
Outputs Sine, TTL (When using an external reference, both outputs are phase locked to the external reference.)
Displays
Channel 1 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
Channel 2 (SR830) 40-segment LED bar graph. Y, θ,
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 X, R, X-noise, Aux 1 or Aux 2
(±10 V), updated at 512 Hz.
CH2 output (SR830) Y, θ, Y-noise, Aux 3 or Aux 4
(±10 V), updated at 512 Hz. X, Y outputs (rear panel) (±10 V), updated at 256 kHz Aux. A/D inputs 4 BNC inputs, 16-bit, ±10 V, 1 mV resolution, sampled at 512 Hz Aux. D/A outputs 4 BNC outputs, 16-bit, ±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 preamp Provides power to the optional SR55X preamps
General
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" (WHD) Weight 23 lbs. Warranty One year parts and labor on defects in materials and workmanship
quantities divided by Aux 1 or Aux 2. 4½-digit LED display with
Y-noise, Aux 3 or Aux 4. The display
In-phase and quadrature components
IEEE-488.2 and RS-232 interfaces
Stanford Research Systems
phone: (408)744-9040
www.thinkSRS.com
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