In resistance thermometers, measurement is based on the change in resistance of precious metals under temperature influence. Since every metal has a specific resistance characteristic, and dU and dR demonstrate approximately proportional (linear) behavior in precious metals such as platinum, the change in resistance dR can be deduced from the voltage change dU by supplying a constant measurement current. The measurement current is selected as low as possible to minimize self-heating of the resistance thermometer.
Thermocouples behave according to the Seebeck effect which describes the production of a charge shift on a conductor when there is a temperature difference along it. The magnitude of the charge shift depends on the material and its electric properties. If there is a conductive connection between two conductors made of different materials on one side and a temperature difference exists there, voltage is applied at the open ends. This voltage depends on the temperature difference and the electric properties of both materials; since they and their characteristics are known, the temperature can be measured via the voltage.
Resistance temperature sensors are classified according to DIN EN 60751:
The first two letters refer to the employed precious metal. The following digit specifies the electrical resistance in ohm at 0 °C.
The classes defined in DIN EN 60751 define the permissible deviation and the measuring range in which these deviations are to be observed.
Class A: +/- (0.15+0.002 x [ t ] ) °C; for platinum temperature sensors between -200 and +650 °C
Class AA: +/- 1/3 x (0.3+0.005 x [ t ] ) °C; for platinum temperature sensors between -200 and +850 °C
Class B: +/- (0.3 +0.005 x [ t ] ) °C; for platinum temperature sensors between -200 and +850 °C
Class 1/6 B: +/- 1/6 x (0.3 +0.005 x [ t ] ) °C; for platinum temperature sensors between -200 and +850 °C
BCID system process connections:
Baumer sensors are suitable for virtually every process connection. Thanks to our more than 40 connection types, you do not need to modify your plant design in any way. The Baumer Connection Identifier (BCID) is a convenient and safe system for identifying the right process adapter in order to integrate your Baumer sensor in the respective application.