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Inertial sensors based on vibrating transducers are becoming increasingly ubiquitous [1]–[9]. Among them, Vibrating Beam Accelerometers (VBAs) are reemerging as a compelling alternative to traditional pendulum accelerometers [10], thanks to their digital output, lower production costs, and inherent digital output [11]–[17].In the pursuit of improved performance, researchers in academia and industry are actively working to reduce error sources in these devices. One effective strategy to minimize common parasitic sensitivities, such as temperature or aging, involves adopting a differential configuration [11]–[17]. In this setup, two beams operate in a push-pull mode, where the frequency of each beam shifts in response to applied acceleration. The difference between these frequencies serves as a measure of acceleration. This method is commonly referred to as Frequency Modulated (FM) mode.However, as previously reported, though not extensively discussed in the literature, this differential mode has a critical limitation. Within a specific range of accelerations, referred to as the lock-in zone, both beams exhibit identical measured frequencies [14]–[19]. This results in a loss of sensitivity to external accelerations, thereby degrading the performance of the sensor.Interestingly, studies have shown that within this lock-in zone, the ratio of the amplitudes of the two beams remains sensitive to external acceleration [20]–[24]. This alternative operational mode, which uses amplitude rather than frequency as the sensing variable, is known as Amplitude Modulated (AM) mode.Recent studies have shown that the lock-in effect observed in axisymmetric Coriolis Vibrating Gyroscopes (CVGs) is a fundamentally physical phenomenon [25] and [26]. This means that CVGs become unresponsive to external angular velocity within the lock-in zone, regardless of whether they operate in FM or AM modes [26].This finding raises a natural question: Is the frequency lock-in observed in differential VBAs also an intrinsic physical effect, or is it merely an artifact of the sensing architecture or signal processing methods? This study aims to explore that question and beyond.We argue that, contrary to the common belief, frequency lock-in in differential VBAs is not a physically intrinsic phenomenon. Instead, it is an artifact introduced by the methods used to detect vibration frequencies. To distinguish this artifact from the well-established physical lock-in observed in other inertial sensors [25]–[27], we refer to it as "pseudo-lock-in."In practical implementations, a frequency detection scheme is essential for monitoring beam vibrations. We demonstrate that a widely used technique, specifically, the zero-crossing frequency counter, is responsible for the apparent pseudo-lock-in behavior. This claim is supported by an analytical investigation of the simplest physical model of a differential VBA [14].We further extend the standard model of a differential VBA, which typically assumes identical beams, to a more realistic case involving unequal beams. Our analysis reveals that the primary effect of beam asymmetry is to shift the center of the pseudo-lock-in range away from zero acceleration.To provide a comprehensive understanding, we derive analytical expressions for the boundaries of the pseudo-lock-in zone and present formulas for its width and position. Based on these findings, we conclude that this analysis may offer a pathway toward resolving the pseudo-lock-in issue in VBAs operating in a differential configuration.