Using IS Barriers with general purpose encoder


Thread Starter

Rob V

I have an issue with an encoder company stating I cannot apply IS Barriers to their devices. Being the designer of a system that uses this device for a speed measurement I have made sure that our controls in conjunction with the encoder is within the operating specifications of the selected IS Barriers. Should they be concerned on how I decide to use their device?

Bruce Durdle

Yes - if there is a bang, and one of their products is involved, they will
bear at least some of the blame.

Unless you have analysed all the failure modes of their encoder, I don't see how you can be sure that the installation is safe. For a component to be certified as IS it must be safe in normal operation and with realistic failures. Also remember that devices fail - will a future replacement still meet your criteria for safety?

You are ultimately responsible for the safety of the installation, but are making a giant gamble on going against a manufacturer's advice in this area.

The manufacturer probably doesn't feel happy enough to declare the encoder as being "Simple Apparatus", either because they don't have sufficient knowledge or don't have the time to spare to do a detailed examination of the circuit.

Do you have a detailed circuit diagram of the encoder, can you be sure that it doesn't contain any components that will generate or store energy outside of the limits in the relevant part of EN 60079 ? If you can't then I wouldn't proceed on your own.