In piezoelectric tube actuators, there are a number of segments or electrodes, some of them, driver electrodes, are excited by applying electrical voltage. As a result, electrical voltage is induced in other electrodes. The measured voltage across driver and non-driver electrodes/segments are called the piezoelectric voltage and the induced voltage respectively. The induced voltage has been used in displacement estimation and control of piezoelectric tube actuators since 2006, while the piezoelectric voltage has been used for the same purpose since 1980's. However, the newly introduced signal of the induced voltage has never been critically assessed for piezoelectric tubes' displacement estimation and control purposes, particularly in comparison with the piezoelectric voltage, another easy to measure electrical signal; this article aims to present such an assessment. In this research, both signals were mapped into displacement through linear and nonlinear models. It was shown displacement can be estimated less accurately via the induced voltage compared to the piezoelectric voltage and the relationship of displacement with the induced voltage presents higher nonlinearity compared to one with the piezoelectric voltage.