We’ve been vibration and shock testing of some heavy equipment designed for the construction environment. This is one of the toughest environments for product environmental testing. It’s wet, it’s dusty, it gets hot and cold… sometimes all at the same time! Not only that but it’s a very physical environment where rough treatment is the norm.
This customer is well versed in the art of protecting their equipment from such conditions using a robust frame with the key part of the product mounted on beefy rubber shock mounts.
This slow motion footage of captured of the unit undergoing shock testing really shows you just how useful these parts are.
Test was being performed to EN 60068-2-27, 10g shocks with a 16ms half sine profile. There is significant pulse pre- and post-loading as the piezolectronic accelerometer I use has a pretty poor low frequency response and this seems to help.
The use of these anti shock mounts isn’t without issue. In this case, the springiness/stiffness of the anti shock mount combined with the mass of the equipment leads to a resonance at around 25Hz with quite large displacement of the main equipment mass.
The losses in the anti shock mounts causes a damping effect leading to a softer, wider resonance. The equivalent of resistance in an LC resonator causing a reduction in the Q of the circuit.
Compared to a much sharper resonance (caused by a different physical structure) the overall gain is much lower. The tradeoff is selecting a stiffer mount to damp the resonances but at the expense of transmitting more force through to the unit under protection.
This Week In The Lab: This fuel injector controller has to withstand significant levels of vibration being mounted inside the engine bay of a high performance racing car.
The manufacturer and end user can’t afford a field failure so we are giving it a literal shakedown.
We are also monitoring the live performance during testing of the ECU to check for failure points or changes in the characteristics of the system
Vibration and shock testing applies to a wide range of products e.g.
- Anything that is mobile or at risk of knocks and shocks in it’s end application
- Industrial equipment working in a plant room or similar environment
- Anything with moving parts; how robust is it? Are there unknown resonant modes lurking?
Get in touch to discuss your vibration testing requirements, we’d be happy to help.
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.