Схемы, платы, компоненты

Наверно используют измерения импеданса на нескольких частотах. Затеяли микруху для металлодетекторов. "Measuring Parallel Resonance Impedance and Inductance with LDC1000 The LDC1000 is an Inductance-to-Digital Converter that simultaneously measures the impedance and resonant frequency of an LC resonator. It accomplishes this task by regulating the oscillation amplitude in a closed loop configuration to a constant level, while monitoring the energy dissipated by the resonator. By monitoring the amount of power injected into the resonator, the LDC1000 can determine the value of Rp; it returns this as a digital value which is inversely proportional to Rp. In addition, the LDC1000 can also measure the oscillation frequency of the LC circuit; this frequency is used to determine the inductance of the LC circuit. The oscillation frequency is returned as a digital value. The LDC1000 supports a wide range of LC combinations, with oscillation frequencies ranging from 5kHz to 5MHz and Rp ranging from 798 Ω to 3.93M Ω . This range of Rp can be viewed as the maximum input range of an ADC. As illustrated in Figure 11 , the range of Rp is typically a much smaller than maximum input range supported by the LDC1000. To get better resolution in the desired sensing range, the LDC1000 offers programmable input range through the Rp_MIN and Rp_MAX registers. Refer to Calculation of Rp Min and Rp Max below for how to set these registers. When the sensor ’ s resonance impedance Rp drops below the programed Rp_MIN, the LDC ’ s Rp output will clip at its full scale output. This situation could for example happen when a target comes too close to the coil."