This video provides an in-depth review and teardown of the Lakeshore M81, a modular precision source and measurement system. The system is presented as a new product category by combining three core metrology concepts: modular source/measure units (SMUs), detachable remote heads for improved signal integrity, and integrated AC/DC lock-in amplification for high-sensitivity coherent measurements. A detailed teardown reveals the sophisticated analog engineering within each remote module—including current, voltage, and source units—showcasing techniques for low-noise, high-isolation, and precision performance. The mainframe's architecture, built on an Android PC with modular data acquisition cards, is also examined. The review demonstrates the system's capabilities through a series of practical experiments, such as characterizing a bipolar transistor's thermal properties, measuring the transfer function of an RC filter, and performing complex lock-in measurements using both internal and external modulation (e.g., an optical chopper) to detect picoamp-level photovoltaic currents and measure liquid levels with ultrasound. The video also evaluates the accompanying MeasureLink software and the instrument's user interface, highlighting its powerful scripting capabilities while offering suggestions for usability improvements.
A Deep Dive into the Lakeshore M81 Modular Source/Measure System
0:00:07 A New Product Category: The Lakeshore M81 system uniquely combines three metrology concepts:
Simultaneous source and measure (like a traditional SMU).
Remote heads, which bring the sensitive analog front-end closer to the device-under-test (DUT) for better signal-to-noise ratio.
Coherent AC/DC lock-in amplification for high-sensitivity measurements below the noise floor.
0:04:51 Hardware Tour and Teardown: The system consists of a mainframe with a responsive articulating touchscreen and individual remote modules for different functions. Teardowns reveal:
Current Measurement (0:07:43): Utilizes a trans-impedance amplifier (TIA) with low-EMF relays and precision resistors on standoffs to achieve high sensitivity and low leakage.
Voltage Measurement (0:10:18): A differential module with extensive switching for AC/DC coupling, various gain stages (x1, x10, x100), and robust input protection.
Source Modules (0:12:57, 0:14:34): Separate modules for a single-ended voltage source and a balanced current source, both featuring high-quality output drivers, protection circuitry, and the ability to generate clean AC and DC signals. The balanced current source notably uses Triax connectors and has internal feedback to control common-mode voltage.
Mainframe (0:17:43): Built around an Android PC, a toroidal transformer power supply, and modular, vertically-mounted data acquisition cards. A shielded Zener diode provides a stable voltage reference.
0:21:05 GUI and Basic Measurements: The front-panel GUI allows for straightforward control of each module's parameters (DC/AC, frequency, amplitude). While functional, the reviewer notes a lack of built-in plotting, math functions, or statistical analysis, suggesting significant room for firmware improvements.
0:36:34 Bipolar Transistor (BJT) Characterization: A practical demonstration using all modules simultaneously to measure a BJT's current gain (beta) and observe its change with temperature. This test showcases the MeasureLink software's ability to automate complex, multi-parameter sweeps.
0:46:29 High-Quality AC Source: The system's AC sources are tested and found to have a clean output with a Total Harmonic Distortion (THD) of approximately -80 to -85 dB, which is critical for performing accurate lock-in measurements at harmonic frequencies.
0:51:48 Advanced Lock-in Demonstration: An RC low-pass filter is characterized. A diode is then added in parallel, introducing non-linearity. The system demonstrates its power by:
Detecting the non-linearity by measuring the signal's second harmonic.
Correcting the measurement by applying a DC offset to the AC source, moving the signal out of the diode's forward-bias region.
0:59:38 Ultrasound Liquid Level Sensing: The M81 is used as a lock-in amplifier to drive an ultrasonic transducer and measure the phase shift of the reflected signal, successfully tracking the changing level of liquid in a container in real-time.
1:02:28 Measuring Photovoltaic Effect with External Lock-in: In a key demonstration, the M81 locks onto an external reference signal from an optical chopper. This allows it to measure the minuscule current (a few nanoamps) generated in a glass diode when struck by a UV laser, perfectly isolating the signal from ambient light interference.
1:07:50 Final Thoughts and Suggestions: The M81 is praised as a powerful, innovative platform with excellent hardware. Key suggestions for improvement include enhancing the built-in firmware with more analysis tools and developing a hardware switching matrix module to easily multiplex the source/measure units across many test points.