Frequently Asked Question

I´m looking at transmitters failure rates of SERH database and I see a category called Fail Dangerous Undetected. But to classify a failure as safe or dangerous it is necessary to know if the transmitter action trips on high or low value. How can you know
Last Updated a year ago

Failures that are classified as Fail Dangerous Undetected are failures that result in a Frozen output. In a 4-20 mA signal range, this means that the transmitter output will be fixed within the healthy transmitter range and regardless of process value will never change output level. Since it is stuck and does not accurately represent the process value, the failure is dangerous, since it is in the normal 4-20mA range it is undetected by any out of range detection mechanism. Therefore all Frozen failures are classified as Dangerous Undetected.

The failure residual failures are also known as no effect failures, These represent failure modes of componetns that are part of the safety critical circuit that do not impact the ability of the transmitter to perform its functions. For example if a filter (resitor/capacitor combination) in an analog output circuit fails, the output signal may become noisy. This however may still be within the safety accuracy range of the transmitter and not prevent the transmitter from indicating a hazardous situation. As such these failures are classified as no effect/residual.

Please Wait!

Please wait... it will take a second!