Hewlett-Packard Thermal Converters are true rms indicators, yielding a dc output voltage proportional to the temperature
rise resulting from the input power. The Models 1l049A, 1l050A and 1l051A offer an exceptionally flat response and
nearly constant impedance over a wide frequency range. These characteristics make the thermal converters ideal to check the response of precision ac voltmeters, oscilloscopes and amplifiers.
They have essentially a flat response from 5 Hz to 10 MHz, and good frequency response from 10 MHz to 100 MHz
Data Sheet