Power sensors NRV-Z51, NRV-Z52 and NRV-Z55 are thermal power sensors for basic instruments NRVS, NRVD, URV35 and URV55. They permit power measurement from 1 pW to 100 mW within the frequency ranges DC ... 18 GHz (NRV-Z51), DC ... 26.5 GHz (NRV-Z52) or DC ... 40 GHz (NRV-Z55) in systems having a characteristic impedance of 50 The thermal conversion principle always permits measurements of the RMS value independently of the waveform and modulation of the test signal. Depending on whether the measured value is output as a power and/or a power level or as a voltage, the average power (and/or the equivalent power level) or the RMS value of the voltage is displayed. All measuring heads are d.c. coupled so that even power in the audio-frequency range can be measured. 1.2 Design and Functioning The power sensor contains a thermo-electric transducer made of silicon by means of semiconductor technology. Due to the power supplied, the 50-Q termination situated on it heats up. immediately next to this resistor there is a thermoelement generating a direct voltage proportional to the heating. As termination and thermoelement are dc-decoupled, the power sensors do not contain, coupling capacitors. This means that even d.c. powers can be measured, and there is no lower cut-off frequency below which matching and frequency response deteriorate again. The direct voltage generated by the thermoelement is amplified by a low-noise amplifier of high sensitivity within the sensor and supplied to the basic unit for further processing. All power sensors contain a data storage in which the parameters obtained during calibration in ---prad u<Sion-a re^tored-in a-narv-vola-tiie-memoryr^The-ba si e-i-ns-trument-reads-out-these~data-arid ta kes account of them when indicating the power measured. Linearity correction of the measured values is effected automatically with the aid of the correction coefficients stored. For temperature correction, the temperature of the measuring head is evaluated additionally via a temperature sensor. For measurements with frequency response correction, the measuring frequency must be entered via keyboard, remote control interface or an analog control input.