Building a Line Impedance Stabilisation Network (LISN) kit for pre-compliance testing
While developing a product to operate on AC power, it is imperative to make sure EMC is controlled to prevent your device from creating harmful interference, or being adversely affected by environmental noise, whatever the cause.
As part of the array of test equipment used to ensure compliance with appropriate standards, eg CISPR/CENELEC/FCC/CE and so on, a LISN is used along with other equipment to measure the high frequency noise component present on the power lines. The device under test is powered, via the LISN, and the noise produced by the device under test in analysed to determine compliance.
Additionally, the LISN is possible to use as a coupling network to inject high frequency signals into the power lines to determine if the device under test is sufficiently immune to power borne noise.
While developing a product of our own, we decided it would be a real advantage to own a good quality AC LISN to enable us to compare performance of our product against that of another similar product. Also, having a LISN would allow us to make base-line noise measurements and then compare any changes we make to the design in order to validate the changes.
Being highly aware of EMC means no surprises at the later stages of compliance testing.
A variety of LISNs are available new, from a number of sources. Second hand, eg via ebay, only larger LISNs seem to be regularly available, with smaller units being purchased immediately in most cases.
However looking at the prices and with all the other test equipment required, it seemed economically viable to make one for ourselves and to sell the end results as a kit.
This LISN kit aims to be a cost effective alternative to ready made LISN units from “the big boys” while performing well across the necessary frequency range.
It is available on ebay https://www.ebay.co.uk/itm/193259636117