FMEDA - SIL assessment

A temperature-sensing device together with a temperature transmitter becomes a temperature sensor assembly. When using FMEDA (Failure Modes, Effects and Diagnostic Analysis) in a SIL verification assessment, also the failure rates and failure modes of the temperature sensing device must be considered. This EXIDA assessment was made for our key transmitter supplier, PRelectronics. In this document typical failure rates for thermocouples and RTD's are stated.
An electrical temperature sensor assembly can be used in a safety instrumented system accordance with IEC 61508 standard. Thermocouple and RTD sensors can be used in conjunction with temperature transmitters, certified for safety relevant applications, such as the PR-electronics transmitters PR5337 / PR6337 / PR7501. Electrical thermometer sensors without a temperature transmitter, for example a resistance thermometer or a thermocouple sensor, is not covered by IEC 61508, since a thermocouple, and a measuring resistor is a simple electrical component, and such component cannot perform any self-diagnostics neither it can detect errors.Typical failure rates for thermocouples and RTD's are listed in the following FMEDA assessment, please click here