True RMS converter#Thermal converters

Thermoelements are instruments for root-mean- determination of the electrical current. With suitable for the respective high-frequency structure, they can be used up to the gigahertz range.

Principle

An electrical resistance (in the simplest case, a heating wire ) is traversed by current. Joule heat generated at the heating resistor and is passed on to the environment. The adjusting themselves with a thermal inertia of heating is proportional to the electric power, as long as the heat transfer occurs by free convection ( and delivery by radiation plays no role ). The increase in temperature produces a DC voltage proportional to a thermal element.

This voltage can be displayed with a suitable voltmeter. In order to it to be able to directly read the rms value of the heating current, a square divided scale is required.

Use

Advantage of this type of measurement is the degree of independence of frequency and waveform. However, disadvantages are a relatively long measurement time as well as the particularly high risk of damaging the transducer for measuring range is exceeded, because the warming increases quadratically with the measuring current. Except for a few applications, in which the current measurement principle has no alternative can be found, Thermoelements are no longer used in the art.