It feels like it has been a busy couple of months here at Unit 3 Compliance with a wide variety of projects coming through the door.
Q1/18 is already shaping up to be busy with some really interesting products booked in for pre-compliance testing and some nice meaty problems to get our teeth into. I’m looking forward to sharing some of the insights I gain from this work with you.
Here’s a quick roundup of what’s been happening…
Our key area of expertise and always the cornerstone of what we do here at Unit 3 Compliance is EMC pre-compliance testing. In the chambers recently we’ve had ticket machines, water boilers, development kits, and a light/motion sensor. Some with problems that we quickly fixed and some sailed through first time.
One particularly interesting product was an industrial lighting system that needed radiated RF immunity testing at 20V/m. This test loves to mess with products by turning on or off semiconductors that were quite happy as they were thank you very much. In this case, there was an transistor based current limiting circuit that, thanks to one of the transistors demodulating the RF carrier, decided to shut down key parts of the circuit. Replacing it with a resistor removed the problem allowing the customers development cycle to continue.
Microwave Antenna Pattern Measurement
A customer has been leasing the anechoic chamber to make some antenna pattern measurements on a complex microwave antenna system. By loading up the quiet zone of the chamber with extra microwave absorber we were able to provide a highly anechoic (low reflection) environment all the way up to 18GHz.
As part of this exercise we made some rough background noise measurements from 2GHz up to 18GHz revealing very little. This suggests that when we reassembled the chamber in its new home we didn’t leave any gaps!
The vibration shaker and amplifier have been fully commissioned after their move. They’ve been getting a good run in performing a 2g sine sweep test on a large 25kg rack mount power supply.
Jigging equipment onto the vibration table is always a challenge, especially for a large and heavy piece of equipment like this one. I like to use 1″ x 1″ x 1/8″ wall aluminium box section (really stiff and light) along with high tensile M10 threaded bar to clamp an EUT of this size. Smaller EUTs can be easily secured to lighter platforms using hot-melt glue, surprisingly effective!
I always find vibration testing fascinating, especially watching various components come in and out of resonance during a sine sweep test. It’s fun to draw parallels between mechanical and electrical resonance, stiffness, impedance and damping.
In this case we found a large resonance that caused a fracture of the base plate due to excessive motion. We suggested a few approaches to stiffening that area, one of which was implemented and successfully removed the resonance.
One piece of equipment I’m going to be designing soon is an LED strobe lamp that synchronises to the output of the vibration controller so that any flexing in resonant modes can be easily spotted. That will make analysis much easier.
We’ve carried our several sets of schematic and PCB design reviews, from motion sensors to heater controllers, from pump monitors to semiconductor development kits.
Our approach is not only to look at EMC / system level but also to question and educate designers on alternative circuit choices based on our long experience in electronics design. This is part of the value that we give to our customers.
In each case we’ve addressed the circuit design, considering the EMI phenomena and levels that the ports of the design will be exposed to. This is where understanding the tests themselves is so important otherwise the circuit could be susceptible to problems.
We also look at design partitioning in some detail. This is one of the easiest ways to achieve good system level performance (and not just from an EMC perspective) by segregating the design into digital, analogue, power supply and I/O areas with the aim of keeping noise currents where they should be and away from their potential victims.