Dose counting system

Abstract

A dose counting system of an injection device or of a module configured to be used with or applied to an injection device, the dose counting system comprising: a sensor arrangement comprising a first sensor configured to output a first signal and a second sensor configured to output a second signal, wherein the first sensor and the second sensor have an angular offset relative to each other and wherein the sensor arrangement is configured to detect movement of a rotary encoder system relative to the sensor arrangement during dosing of a medicament; and a processor configured to: compute numerical derivatives of the first signal and the second signal; detect a peak in the derivative values of the first signal and a peak in the derivative values of the second signal when the first and second derivative signal values exceed a predefined threshold; determine that a unit of medicament has been administered when the peaks in the derivative values of the first signal and the derivative values of the second signal are simultaneous, the peak in the derivative values of the first signal has a different sign from the peak in the derivative values of the second signal and the peak in the derivative values of the first signal has a different sign for the previous peak in the derivative values of the first signal; and determine a medicament dosage administered by the injection device by counting the administered units of medicament.