Measurement Uncertainty of the Mains LISN

In this article, I focused on the key parameters of the lisn. However, what is missing are some words about the actual reason for some of these.

My project-log just mentioned the magnitude of the impedenace. But there are also limits for the argument of this complex value. What this means, is shown below.

So the actual input impedance of our LISN will be somewhere within the circle defined by the 20% tolerance of the magnitude and 11,5° of the phase angle. To estimate the uncertainty, we now need to define a worst-case source impedance. Luckily, some relatively simple methodology has already been descibed in this paper:

Stecher, Manfred. “EMC ’ 09 / Kyoto Uncertainty in RF Disturbance Measurements : Revision of CISPR 16-4-2.”

What is suggested is in prinziple to model a source with variable variable impedance. You could think of this like this:

Unfortunatly, modeling something that would cover any value from 0 to ∞ is pretty nasty. However, Manfred came up with something pretty obvious. He's modeling it via reflection coefficient. Hence, we cover the whole (0..∞ ± j 0..∞)Ω range with ease.

My aproach is now quite trivial. I'll show you how you could simply do similar estimations yourself.

What is measurement uncertaintiy

First of all, we need to consider how we define our uncertainty. In case of measurements with our LISN, we need to see how much a reading would change if we change our measurement instrument. Lucily, we have a reference for the impedance of a LISN.