To make sure your measurements are done in the best possible way, focus on minimizing noise in your everyday Otii measurements.
The smaller the signal you want to measure, the more critical it is to cancel all surrounding noise sources and their path into your setup. You’ll need the signal to noise ratio to be as high as possible.
The 50 Hz magnetic field (60 Hz in some countries) from the power mains will be induced more or less in any conductor anywhere. That’s why you can see it on your measured signal.
According to the transformer principle, one or several conductors in our circuitry induce the 50 Hz pickup that usually proves problematic. Screening – the way radio frequency circuits with coaxial cables us it – won’t work for the induced 50 Hz field.
The trick is to minimize induction through two actions:
ACTION 1: Minimize the loop area
ACTION 2: Increase the distance between your equipment and the noise source
Increasing the distance between your equipment and the noise source can be very useful, because the magnetic field loses its intensity proportional to 1/r3.
WATCH OUT FOR:
Please pay attention to the fact that, if you minimize the 50 Hz noise, you will, of course, minimize higher frequency noise as well.
If your device under test (DUT) has other electrical or galvanic connections* to the surrounding world, there will probably be a ground loop. Ground loops are well known for introducing many kinds of disturbances in electronic systems. Check this list when you connect your Otii in a measurement setup:
* Examples of connections that generate a ground loop:
In the above example, remove the power to the computer to disconnect the ground loop and minimize the risk of 50 Hz and more high-frequency disturbances.
If the power from a USB-only connected Otii is not enough, you need to connect something to the DC port. However, a noisy power supply connected to the DC port of your Otii can introduce disturbances in your measurements. You should also keep in mind that the noise from the power supply can change depending on the load. In other words, you may not always see the noise in your measurements.
If you choose to power your Otii with an external DC adapter, we recommend that the adapter is:
Many AC/DC adapters with a rating above 2A can be quite noisy, so be careful concerning the quality when you want proper measurements while you work in these ranges. Our recommendation would be XP Power VEL18US090-EU-JA (available e.g. at Digi-Key) – an adapter that has received plenty of good feedback.
Please keep in mind that you’re facing a very common but complex problem that requires several actions before it can be solved. To minimize the noise in your measurements, you’ll probably need to test different ways of removing the disturbances while you monitor the result.