ISO 23551-6:2014 applies to thermoelectric flame supervision controls for gas burners and gas-burning appliances of nominal connection size up to, and including DN 50, that can be used and tested independently of these appliances.
These thermoelectric flame supervision controls are suitable for fuel gases, such as natural gas, manufactured gas, or liquefied petroleum gas (LPG) at inlet pressures up to and including 50 kPa.
ISO 23551-6:2014 covers type testing only. It is neither applicable to the thermocouple nor to controls which use auxiliary energy (e.g. electrical energy supplied externally).