Tech Explained: Acoustic Cameras

Earlier in the week, a friend sent me a video of a product from Fluke that visualizes air leaks and other noises. I had no idea such a technology existed. Spent some time learning more, and now I wanted to share what I found.

Acoustic cameras are essentially devices that can “see” sound. Think of them as thermal imagers, except for sound. They combine a specialized array of MEMS microphones with a camera interface to capture and display noise sources as colourful, real-time heat-map images. While this might sound futuristic, the tech has been around for the last few decades, but I never knew. 
So how does it work? An array of microphones picks up sound waves from different directions. These signals are then processed by a beam forming algorithm that calculates the precise location of each sound source. The system superimposes a heatmap-like overlay onto a visual image or video feed, highlighting exactly where noise originates. It’s like having a set of highly trained ears that can pinpoint the faintest hiss or hum in a busy environment. Some units have audio freq range selection so that you can select to really reduce surrounding noise to focus on a specific band.

Its applications are varied. Factories use them to quickly spot air leaks, carmakers use them to reduce cabin noise, and mechanics use them to find hidden unusual vibration noises in factory equipment. Some factories rely on them for preventative maintenance, before they become costly. Environmental folks employ these tools for tasks like monitoring wildlife habitats or measuring noise pollution levels. It’s used to detect electric partial discharges in High voltage electric power delivery systems. Corona discharge, arcing emits ultrasound that can be picked up via this tech.

The distance of capture is not that high though. If it was, I would have loved to put this up on a drone and get a bird’s eye view of the city and its noise level sources. Nice little tech if you ask me.

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Back To Basics: 4-wire Kelvin Connection

This is a simple resistance measurement technique and fairly widely known, but I rarely see folks whom I usually interact with, using it. The name “Kelvin” comes from Lord Kelvin, who made a bridge circuit to measure smaller resistors.

To measure any resistor, the default method used is to pass a known current through a resistor and measure the voltage across it. Then via Ohms law calculate the resistance value. To understand why 4-wire is needed, you need to understand the issue with a 2-wire measurement. In 2-wire measurements, the resistance of the wires and contacts adds to the resistance of the component under test. This becomes a problem when the component value under measurement is very small. Check images. As the current in both arms are the same, the voltage measured includes the voltage drop across lead resistors also.

The 4-wire method solves the issue by using one pair of wires to supply the current and another pair to measure the voltage drop across the device. This separation ensures that the voltage measurement is not influenced by the voltage drop in the current-carrying leads, resulting in a much more accurate reading. Since the current flowing to the voltage measurement part is negligible (because of high impedance), measured voltage accurately reflects the resistance of the component alone.

Their application mostly involves measuring milliohm-level resistance values. These can be for measurement of shunt resistors, PCB traces, internal battery resistors. They find their way in precision and calibration instruments.

There are also shunt resistors with 4 terminals that allow you to do this measurement on an actual PCB. Please check my older posts or search the website on how to place and route them in PCBs. Also, if you want to use them, you will get 4 wire Kelvin style connectors with clip on leads. Worth purchasing you if you do a lot of low value resistance measurements.

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