A temperature controller, with an analogue PCB, a digital PCB and a LED
The product was required to meet the heavy industrial limits for radiated
immunity, but failed at a range of frequencies around 35 MHz with the
temperature reading error well outside of the customers specified accuracy. At
a relatively low frequency it was likely that one or more cables were
responsible for this noise coupling. Cables were disconnected or suppressed one
at a time until the coupling route was identified.
The system could now be removed from the chamber and the PCB together with the
coupling cable placed on the ETSi 4334. An external noise source was used in
inject a 35 MHz signal into the cable. An X-Y plot of the PCB at the same
frequency showed the areas which were affected; In this case the input stages
of a differential amplifier. From this information the design engineers were
able to apply suitable filtering to just those areas of the PCB that needed it.
The temperature controller was then re-assembled and found to be compliant when
returned to the chamber.
The use of the ETSi Scanner led to a solution which filtered the noise from the
affected circuitry, and avoided expensive screened cable or impracticable