SRS Labs SR530 manual Reference Mode, Reference Display, Phase Controls, Time Constant

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going transitions of the reference input. This mode triggers on a negative pulse train or on the falling edges of a TTL type pulse train (remembering that the input is ac coupled). The pulse width must be greater than 1 ∝ S.

Reference Mode

The REFERENCE MODE indicator toggles between f and 2f whenever the MODE key is pressed. When the MODE is f, the lock-in will detect signals at the reference input frequency. When the MODE is 2f, the lock-in detects signals at twice the reference input frequency. In either case, the reference oscillator has a maximum frequency of 100 KHz, thus, when in the 2f mode, the reference input frequency may not exceed 50 KHz.

Reference Display

The REFERENCE DIGITAL DISPLAY shows either the reference oscillator frequency or phase shift. The displayed parameter toggles between the two whenever the SELECT key is pressed. The appropriate scale indicator below the display will be on. It is useful to check the frequency display to verify that the lock-in has correctly locked to your reference. The reference frequency is measured to 1 part in 256 resolution at all frequencies. The display reads .000 if there is no reference input and 199.9 kHz if the input frequency exceeds 105 kHz.

Phase Controls

The phase shift between the reference oscillator of the lock-in and the reference input signal is set using the four keys in the PHASE section. The two keys below the FINE label increment the phase setting in small amounts. A single key press will change the phase by 0.025 degrees in the desired direction. Holding the key down will continue to change the phase with larger and larger steps with the largest step being 10 degrees. The two 90° keys are used to change the phase by 90 degree increments. The upper key will add 90 degrees and the lower key will subtract 90 degrees. Holding both keys down at once sets the phase shift back to zero. The REFERENCE DIGITAL DISPLAY automatically displays the phase whenever any of the PHASE keys are pressed. The phase ranges from -180 degrees to +180 degrees and is the phase delay from the reference input signal.

Time Constant

There are two post demodulator low pass filters, labeled PRE and POST. The PRE filter precedes the POST filter in the output amplifier. Each filter provides 6 dB/oct attenuation.

The PRE filter time constant ranges from 1 mS to 100 S and is selected by the two keys below the PRE filter indicator LED's. Holding down either key will advance the time constant four times a second in the desired direction.

In many servo applications, no time constant is needed. The SR530 may be modified to reduce the output time constant to about 20 ∝ S. Contact the factory for details.

The POST filter time constant can be set to 1 S or

0.1S, or can be removed altogether, NONE, using the two keys below the ENBW indicators. When set to NONE, the total attenuation is that of the PRE filter, or 6 dB/oct. When the POST filter is 1 S or 0.1S, the total attenuation is 12 dB/oct for frequency components beyond the larger of the POST and PRE filter bandwidths (reciprocal time constant).

Noise Measurements

When the DISPLAY is set to X NOISE Y NOISE, none of the PRE and POST indicator LED's are on. Instead, one of the two ENBW indicators will be on, showing the Equivalent Noise Bandwidth of the rms noise calculation. The ENBW is set using the keys below the ENBW indicator LED's (same keys as used to set the POST filter). The PRE filter keys do nothing in this case. Pressing the upper key when the bandwidth is already 1 Hz will reset the rms noise average (output) to zero, restarting the calculation. Likewise with pressing the lower key when 10 Hz is already selected.

The noise is the rms deviation of the output within a 1 or 10 Hz equivalent noise bandwidth about the reference frequency. A dc output does not contribute to the noise, the noise is determined only by the ac 'wiggles' at the output. By measuring the noise at different frequencies, the frequency dependence of the noise density can be found. This usually has the form of vnoise ~ 1/f. The noise computation assumes that the noise has a Gaussian distribution (such as Johnson noise). Since the computation takes many time constants (reciprocal ENBW), the noise output

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Contents Model SR530 Page Table of Contents Appendix C Gpib NON-OPERATING OperatingPage SR530 Specification Summary Gpib DemodulatorFront Panel Summary Enbw Abridged Command List Status Byte Definition Configuration SwitchesSensitivity Signal InputsSignal Filters SR510 Guide to Operation Front PanelChannel 1 Display Dynamic ReserveStatus Display SelectOffset Channel OutputOutput Channel Rel ChannelRcosø Output Expand ChannelChannel 2 Display Auto Phase Reference Input Rsinø OutputTrigger Level Time Constant Reference ModePhase Controls Reference DisplayDefaults PowerLocal and Remote SR530 Guide to Operation Rear Panel Page Front Panel Status LEDs Command SyntaxSR530 Guide to Programming Communicating with the SR530Try-Out with an Ascii Terminal RS232 Echo and No Echo OperationLOW Norm High SR530 Command ListN1,n2,n3,n4 Page Status Byte ErrorsBit Common Software Problems include ResetTrouble-Shooting Interface Problems Common Hardware Problems includeSR530 with the Gpib Interface SR530 with the RS232 InterfaceGpib with RS232 Echo Mode Serial Polls and Service RequestsSR530 with Both Interfaces Measurement Example Lock-in TechniqueShielding and Ground Loops Understanding the SpecificationsPage Page SR530 Block Diagram DC Amplifiers and System Gain Signal ChannelPhase Sensitive Detectors Reference ChannelCircuit Description Demodulator and Low Pass Amplifier Reference OscillatorMicroprocessor Control Analog Output and ControlExpand Front PanelRS232 Interface Power SuppliesGpib Interface Amplifier and Filter Adjustments Multiplier AdjustmentsCalibration and Repair Replacing the Front-End Transistors Notch FiltersNon-Essential Noise Sources Appendix a Noise Sources and CuresPage Page Case 2 RS232 with Control Lines Case 1 The Simplest ConfigurationAppendix B Introduction to the RS232 Baud RateFinal Tip Stop BitsParity Voltage LevelsBus Description Appendix C Introduction to the GpibProgram Example IBM PC, Basic, via RS232 Appendix D Program ExamplesProgram Example IBM PC, Microsoft Fortran v3.3, via RS232 Page #include stdio.h Program Example IBM PC, Microsoft C v3.0, via RS232Page Program Example 4 IBM PC,Microsoft Basic, via Gpib ′INCREMENT X6 Output by 2.5 MV Program Example HP85 via Gpib Documentation Dpdt Oscillator Board Parts ListPC1 SW1BT1 Main Board Parts ListBR1 BR2SR530 Component Parts List SR530 Component Parts List CX1 22U MINPIN D Gpib ShieldedFU1 CY1MPSA18 SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List 4PDT SPSTX8SR513 Assy SR530 Component Parts List Static RAM, I.C Z80A-CPU#4 Flat TIE AnchorTranscover MicaFront Panel Board Parts List RED LD2 LD1LD3 Quad Board Parts List SR530 Component Parts List PC1 SR530 Component Parts List Miscellaneous Parts List SR530 Component Parts List

SR530, Lock-In Amplifier specifications

The SRS Labs Lock-In Amplifier, model SR530, is a powerful tool designed for high-precision measurements in the realm of scientific research and industrial applications. This state-of-the-art instrument excels in extracting small signals from noisy environments, making it an invaluable asset for experiments in fields such as physics, engineering, and materials science.

One of the main features of the SR530 is its ability to perform synchronous detection, which is key to improving signal-to-noise ratios. By utilizing a reference signal, the device correlates the incoming signal with the reference to effectively filter out noise, allowing for the accurate measurement of weak signals that might otherwise be obscured. This process of phase-sensitive detection is fundamental to the operation of the Lock-In Amplifier.

The SR530 offers a wide frequency range, covering from 0.1 Hz to 100 kHz. This broad frequency response allows it to handle a diverse array of signals, making it suitable for various applications including optical detection, capacitance measurements, and in many cases, voltammetry. The device is also equipped with multiple inputs and outputs, facilitating the integration with other laboratory equipment and enabling complex experimental setups.

Precision is further enhanced with its adjustable time constant, which allows users to optimize the response time based on experimental needs. The user can choose time constants from 10 microseconds to 10 seconds, accommodating fast dynamic measurements as well as those requiring stability over longer durations.

Another remarkable characteristic of the SR530 is its digital processing capabilities. The device features a highly accurate digital voltage measurement system, minimizing drift and ensuring long-term stability. Additionally, the use of microprocessors enhances data handling and allows for features such as programmable settings, facilitating automated measurements.

Moreover, the SR530 includes a range of output options, including analog outputs, which can be used for direct signal processing, as well as digital interfaces for integration with computers. This ensures that users can not only capture high-fidelity data but also analyze and display it efficiently.

In conclusion, the SRS Labs SR530 Lock-In Amplifier stands out due to its sophisticated technology, versatile features, and robust performance. Its precision, flexibility, and ease of use make it an ideal choice for researchers and engineers looking to unlock the potential of weak signal measurement in complex environments.
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