industrial protections for electronic design

[Morgoroth]

Hi all,

For a project, I need to design an acquisition system for few analog signal by RF in an industrial environment. The RF and programming are not a problem, however, I have no experience on industrial electronic design. On google you can find a lot of information over electronic protection, who involve usually resistors, few zeners, RC filters, etc etc... however, I have the opportunity to open few industrial devices (PLC DACs, PID controllers, etc...) and the protections are quite simple, so seems like in practice the protection level is not that high, and I wonder if there is some standard for this, or in the real world which is enough.

In other threads, I've read that telecommunication equipments are heavily protected much more than the industrial ones I've opened, maybe under a different standard, not sure.

Thanks in advance,

JP

[FrankBuss]

There are testing standards, for military, medical and commercial devices, see here on Wikipedia for a start. Then you design your circuit that it survives such tests.

Once I designed a medical device and hired a professional to check the inputs and outputs. His suggestion looked like this:



and it survived the ESD tests for medical devices. But this was for slow digital inputs, would be different for fast inputs.

All outputs required EMI filters (values depending on the required frequency on the output pin) and again a 1nF capacitor to GND, to short some of the energy of ESD impulses (there were only relatively slow outputs again, like RS485 with 9600 baud).

[Gyro]

I hope you didn't pay him much, for that input circuit anyway! 

[retrolefty]

Keep in mind that some industrial settings have special requirements for explosive atmosphere or potentially explosive atmosphere, named 'intrinsically safe'. This requires current limiting such that no electrical spark of sufficient energy can be generated out in the plant.

 In my day there was class 1, division 1 and class 1, division 2. Later they changed to a group naming.  Many/most petrochemical plants fall under these kind of 'rules'. I'm sure EU has related classification standards. These standards I believe must be 'certified' by a third party. Before I retired in 2007 we still could not carry cell phones into the plant unless they carried proper intrinsically safe rating, which most (any?) don't.



 

[FrankBuss]

I hope you didn't pay him much, for that input circuit anyway! 

Something wrong with it? It was not cheap, but it was a review of the whole circuit and PCB layout that it meets the standard, e.g. for safety, ESD, EMI etc. and I had to change some other things. But it was successful, because the product passed all tests at a certified lab, including EMI, which is expensive if you have to fix something for this later and pay for the tests again. This is the webpage of the guy who did the tests: http://www.analogconsultants.com (he doesn't care about fancy website design ). I can highly recommend him and would hire him again for similar tasks. He could help with best practices for industrial protection as well.