In an embodiment, an apparatus for determining a value of a parameter related to electrical permittivity of a fluid includes capacitor formed by at least one electrode on a first side of a dielectric barrier and at least a part of an electrically conducting housing surrounding the barrier. The housing is adapted for being sealingly attached to a container so as to allow the fluid to be characterized to occupy a space between the housing and a side of the barrier, and an electronic relaxation type oscillator circuit is arranged on a miniature circuit board being fit to the housing and connected with the capacitor. An electrical power supply is connected to supply electrical power to the oscillator at an ultra-stable supply voltage, and a frequency measuring device coupled to the oscillator circuit for providing a measured oscillator frequency representing the electrical permittivity dependent on capacitance and resistance.