A method, a computer program product, a device and a monitoring arrangement for monitoring operation of an exchangeable unit in a machine. The converter has an amplifier that receives at least one of a plurality of first reference voltage signals and outputs a plurality of coarse bits. Additional benefits are high resolution in the area where the gap between center conductor and probe is small, smooth increase of proximity between probe and center conductor and the possibility to compensate for the negative phase slope at higher GAMMA, native to traditional slide screw tuners.