Dose logging sensor system with error detection feature

An add-on device adapted to be releasably mounted on a drug delivery device, the drug delivery device comprising:

• a drug delivery device housing,
• a drug reservoir or structure for receiving a drug reservoir,
• drug expelling structure comprising:
• a dose setting member allowing a user to set a dose amount of drug to be expelled from the drug reservoir, and
• a release member actuatable between a proximal position and a distal position, the proximal position allowing a dose amount to be set, the distal position allowing the drug expelling structure to expel a set dose,
• the add-on device comprising:
• electronic circuitry, comprising:
• a sensor system adapted to measure a property of the drug expelling structure during drug expelling indicative of the size of the expelled dose amount, the sensor system being actuatable between a low-power off-state and a high-power on-state,
• a switch for actuating the sensor system between the off and on state, the switch being actuated when the release member is actuated between the proximal position and the distal position,
• a memory adapted to store (i) log data related to measured property values and (ii) log data related to an error period, and
• wireless transmitter structure for transmitting data to an external receiving device,
• wherein the electronic circuitry is adapted to:
• with the switch in the on-state, actuate the sensor system from the high-power on-state to a low-power sleep state after a given amount of time and store in the memory a corresponding error start timestamp,
• with the sensor system in the low-power sleep state, detect when (i) the switch is actuated from the on-state to the off-state, or (ii) the switch is actuated from the off-state to the on-state, and store in the memory a corresponding error end timestamp, this creating an error period, and
• control the wireless transmitter structure to transmit (i) log data related to measured property values and (ii) log data related to the error period,
• whereby an external receiving device can indicate to a user that the sensor system has been in an error state for a period of time corresponding to at least the error period.

A display device adapted to display drug dose log data, comprising:

• a memory adapted to store (i) drug dose log data and (ii) log data related to an error period,
• a display for displaying log data to a user,
• user request input structure,
• wireless receiver structure adapted to receive (i) drug dose log data and (ii) log data related to an error period from an external drug dose logging system, and
• electronic circuitry adapted to:
• receive a request for displaying log data stored in the memory,
• when a request for displaying log data is received, prompting the user to update the memory by actuating the external drug dose logging system to transmit at least the most recently data stored therein, and
• when log data related to an error period is received, control the display to indicate to the user that the sensor system has been in an error state for a period of time corresponding at least to the error period.

A method of controlling display of log data stored in a log memory, comprising the steps of:

• receiving a request for display of log data from a user,
• prompting the user to update the log memory by transmitting updated log data from a logging device,
• receiving from the logging device (i) updated log data, and/or (ii) updated log data related to an error period for the logging device, and
• displaying (i) updated log data, and/or (ii) displaying an indication that the logging device has been in an error state for a period of time corresponding at least to the error period.