I recently saw a post from one of the process automation world’s newest bloggers, Dave Harrold, on the topic of power and grounding. The post, A Non-sexy Means to More Reliable Operations spoke to the importance of power and grounding. Dave summed it up well:
I’ve been around this stuff for a very long time and I’m confident that if you spend eight hours per month for the next six months finding and fixing instrumentation and control system power and grounding problems that your instrumentation, control, and safety systems will perform much more reliably and you know what that means – when the boss is happy, everyone is happy.
If you have power and grounding issues, Dave referenced a great book Control System Power and Grounding Better Practice he wrote with Emerson’s Dave Brown and Roger Hope. It’s being used at a number of universities as part of their engineering curriculum.
I caught up with Dave Brown, a Principal Engineer in Emerson’s Process Systems and Solutions technology organization for his thoughts on Dave Harrold’s post. He gave me a great analogy. It’s like building a house. Your power and grounding is like the foundation. The better it is designed and built, the fewer problems you will have with everything else. Automation systems, safety systems and all your instrumentation and plant equipment will perform better.
So what does all this have to do with too much heat? Dave has also just written a whitepaper entitled Effects of Heat and Airflow inside an Enclosure. It discusses how mean-time-between-failure (MTBF) numbers are based on Mil standard specs of 25 degC. For every 10 degC rise above this amount, the MTBF cuts in half. Although equipment can be rated much higher, like 60 degC, its likelihood of failure rate will increase.
Hmmm… this makes me want to check the temperature in my audio/visual cabinet at home.
Equipment with several years of run-time use actual field data for the MTBF calculations. The numbers usually improve given the conservation nature of the Mil standards.
Dave’s whitepaper offers some practical solutions for heat dissipation from the placement of the equipment within the cabinet to the auxiliary designs for cooling and air flow.