or, generates the gate pulse during which reference pulses are counted.

I/O addresses are decoded by U705, U706, and U707. The microprocessor controls the lock-in functions through I/O ports U714-U721. U713 generates an interrupt to the CPU every 4 msec to keep the microprocessor executing in real time.

RS232 Interface

The RS232 interface uses an 8251A UART, U801, to send and receive bytes in a bit serial fashion. Any standard baud rate from 300 to 19.2K baud may be selected with the configuration switches. The X16 transmit and receive clock comes from counter 2 of U704. The RS232 interface is configured as DCE so that a terminal may be connected with a standard cable. When a data byte is received by the UART, the RxRDY output interrupts the CPU to prevent the data from being overwritten.

GPIB Interface

The interface to the GPIB is provided by U802, an MC68488 General Purpose Interface Adapter (GPIA). The GPIB data and control lines are buffered by drivers U808 and U811. Because the GPIA uses a 1 MHz clock, wait states are provided by U805 to synchronize I/O transactions with the 4 MHz CPU. The GPIA interrupts the CPU whenever a GPIB transaction occurs which requires the CPU’s response. (The GPIB address is set by switch bank SW1.)

Power Supplies

The line transformer provides two outputs, 40VAC and 15VAC, both center tapped. The transformer has dual primaries which may be selected by the voltage selector card in the fuse holder. The 15VAC is rectified by diode bridge BR2 and passed to 5V regulator U909. The output of U909 powers the microprocessor and its related circuitry. The 40VAC output is half-wave rectified by BR1 and regulated by U901 and U902 to provide +20V and -20V. These two dc voltages are then regulated again by 15V regulators U903-U908. Each 15V regulator powers

aseparate section of the lock-in to reduce coherent pick up between sections. U911 and U912 provide plus and minus 7.5V and U910 generates +5V for the analog circuits.

Internal Oscillator

The internal oscillator is on a small circuit board attached to the rear panel of the instrument. Local regulators, Q1 and Q2, provide power to the board. The VCO input is internally pulled up by R12. This pulls the VCO input to 10V when the VCO input is left open. 2/4 U1 translates the VCO input voltage to provide a negative control voltage to U2, the function generator. P3 adjusts the VCO calibration. U2 is a sine wave generator whose frequency range is selected by the VCO Range switch and capacitors, C4-C6. P2 adjusts the sine wave symmetry at low frequencies. 4/4 U1 buffers the output of U2.

P1 adjusts the amplitude of the output sine wave. The output amplitude on the SIne Out is selected by the amplitude switch. The output impedance is 600 Ω.

37

Page 40 Page 42
Page 41
Image 41
SRS Labs SR530, Lock-In Amplifier manual RS232 Interface, Gpib Interface, Power Supplies
Page 40 Page 42

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.
Top Page Image Contents