SR510 and SR530 Lock-In Amplifiers
Two stages of filtering follow the phase sensitive detector.Time constants can be chosen as long as 100 seconds formaximum noise reduction, or as short as 1 ms (20 second filter similarly provides 50 dB of rejection at thesecond harmonic of the line frequency. The third filter is a
band pass filter which automatically tracks the reference
frequency. These three filters can eliminate much of the noise
in the signal before it is amplified. Reference Input Output Time Constants 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 beforethe lock-in cannot measure a signal with its specifiedaccuracy.The SR510 and SR530 have a dynamic reserve of between 20 dB and 60 dB, depending on the sensitivity scale. Selecting
the band pass filter adds an additional 20 dB of dynamic
reserve, making the maximum dynamic reserve for these lock-ins 80 dB. µ s withmodification) for use in real-time servo loops. The two filter
stages allow a rolloff of 6 or 12 dB/octave. Offset and Expand The reference input can be set to lock to sine waves or toeither edge of a pulsed reference. The reference frequency
range is 0.5 Hz to 100 kHz, and detection at both the
fundamental and second harmonic of the reference is allowed.
Aconvenient, built-in frequency meter constantly measures
and
displays the reference frequency with 4-digit resolution.
The reference can be phase shifted with 0.025° resolutionfrom the front panel, or shifted in 90° increments for easymeasurement of quadrature signals. The SR530 has an auto-
phase feature that lets you quickly determine the phase of the
signal relative to the reference with a single key-press. Dynamic Reserve The SR510/SR530's offset and expand features make it easyto look at small changes in a large signal. Output offsets of 0 % to 100 % of full scale can be selected manually or byusing auto-offset, which automatically selects an offset equalto the signal value. Once the signal is offset, a 10 Precision analog meters and 4-digit digital
displays arestandard on both lock-ins. On the SR510, you can selectdisplays of the signal amplitude, the signal offset, or themeasured noise. On the SR530, the first pair of
displays show
the signal components in rectangular form (X and Y), polar
form (R and × expand isavailable to provide increased resolution when looking at
small changes from a nominal value. θ ), the offset, noise, or the value of the rear-panelD/Aoutputs. The other digital
display on both lock-ins can be
configured to show either the reference phase or the
reference frequency. Analog and Digital Displays Noise Measurement Internal Oscillator The SR510/SR530's noise measurement feature lets youdirectly measure the noise in your signal at the reference frequency. Noise is defined as the rms deviation of the signal
from its mean. The SR510/SR530 will report the value of the
noise in both a 1 Hz and 10 Hz bandwidth around the
reference frequency. An internal voltage-controlled oscillator provides both anadjustable-amplitude sine wave output and a synchronous,
fixed-amplitude reference output. The sine wave amplitude
can be set to 0.01, 0.1 or 1 Vrms, and it can drive up to 20 mA.
The oscillator frequency is controlled by a rear-panel voltage
input and can be adjusted between 1 Hz and 100 kHz.
Typically, the sine wave output is used to excite some aspect
of an experiment, while the reference output provides a frequency reference to the lock-in. SR510 Lock-In Amplifier
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