Hello,

Perhaps a bit late, but the EDUCYPEDIA has some links on EMC-EMI that might interest you:
http://educypedia.karadimov.info/electronics/emc-emi.htm

Bertus

 

Watch out for the leakage current of whatever protection you throw at the analog inputs. TVS and MOVs have pretty large leakage, and some diodes do as well. With micropamps of measurement current, you will probably have issues when subjected to the temperature extremes, which for industrial I believe are -40°C to +70°C. Also check the criteria for bursts and surges so that your device can survive those (i.e. does it need to keep telling the correct state even when subject to fast transients..)
A 1kV surge, even when coupled through the 42ohm and 0.5uF can blow simple I/O protection into a mist of copper and silicon pretty easily - shielded cables might give you a better ability to withstand those due to differnent connections of the test setup.

Thanks for the input. The basic circuit has been working for many years in power stations. Basically what i am doing is adding some features like relay delay, extra leds, potentiometer for sensitivity and tightening up on the EMC side by adding line filter. There is no way to 100% protect the sensor inputs in these applications and I don't think anyone does.

Having worked with this type of equipment for 20 years, I have only ever seen the transistors blow and the TLC3702CP blow.

The basics of the system is that 6v 50 microamps is applied to a sensor, when water rises to the sensor level the circuit is complete, so basically an on off switch. The op amp then outputs to relay and leds. Because the sensor is inside a vessel it is quite well protected, it is only the return circuit that is earthed to the vessel that can be vulnerable. Because the relay has a delay action, this helps with small breaks in the signal.

 

The product will only be EMC tested in U.K. For CE marking and that's a one off cost.

You can't get a CE mark with just EMC testing. I was under the impression that the cost of a CE Mark was even more onerous than UL. If it is a one off cost with no recurring amount -- what is that alleged one time fee?
Our solution was to offer customers a choice. You can have the product for price X without the certification. If you want the certs then the price is 3X. That is about what is required to make small volume production economically viable. But hey you're obviously smarter than I am -- right?

 

Yes that is true but there is no legislation in UK to say that you have to use a certified body to pass a product. In Europe all electrical items have to be CE marked (it is illegal to sell without) but is can be done through self certification on some types of products, high risk products have to have notified body approval. It is made up of EMC testing and also safety testing. I will use a proper test house to ensure the products pass EMC testing and then the rest will be done via the compilation of a technical file and a report following the BS EN 61010-2-010:2014 standard for this type of equipment.

The only ongoing fees are when the standards are undated and products need to be redesigned or retested.

I work for a company that makes flame scanners etc for power stations, oil refineries etc and we are heavily involved in ATEX and IECEx products and the standards they have to be made to. I have also dealt with FM in USA before and their yearly fees for a piece of paper.

 

Is FM the fire protection and building materials certification?

 

Factory Mutual are a notified body, we used them to certify electronic drum level indicators for use in power stations in the past.