The determination of e.g. the phase position of a signal used for measurement purposes is often difficult if this signal is superimposed by a strong noise after it has passed a measurement path. For such questions, lock-in amplifiers can be used in which a signal of the same frequency shifted by means of a phase shifter is compared with the phase position of the signal used for the measurement; the shifted signal has an exactly known phase position compared to the measurement signal at the beginning of the measurement section. The phase position of the useful signal in the noisy measurement signal can be determined by means of varying phase shifter settings. This phase determination requires a suitable detection and therefore i.a. long measurement times (integration duration, time constant), whereby the phase reference with regard to the high-frequency generator signal, and thus the actual measurement result of a measurement, is only the setting of the phase shifter, in a lock-in amplifier arrangement using a switch function from a strongly disturbed signal Periodically, with a frequency close to the measurement signal frequency, complementary sections are taken, which are alternately switched to two integrators and integrated, and a digital signal is generated from the difference of the integral values by means of a comparator, there are (low-frequency analog or digital) signals, If two clock signals with closely spaced frequencies are used, a measuring signal can be derived from each of these clock signals for two lock-in amplifiers and the control signal for controlling the switch function can be provided the; In addition, a digital beat signal can be formed as a reference from both clock signals, by means of which the phase position of the measurement signal can be precisely assigned. This means that cross-working double lock-in amplifier arrangements are available, the new measurement methods using phase and transit time determination of signals.
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