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System requirements

This document describes the system requirements.

Product overview

The product consits of an embedded device, which monitors the water level of a given container. It communicates to a remote service where data is stored and can be accessed by a user

Definitions

  • Sensing unit is the device that measures the water level.
  • Firmware is the application running on the sensing unit.
  • Software is the backend application that receives data from the sensing unit and provides a web page for the user to view.

Requirements

Performance requirements

SRP.01 Water level accuracy and range

Water level accuracy shall be ±10cm and a range of 0-1.5m.

Acceptance critera:

  • Measured water level is within ±10cm at at least three points spread across the measuring range.
  • Measuring outside water reports 0-5cm. (No negative measurements)
  • The system measures ±10cm when put at a depth of 1.5m.

Source: UN.2

Output: Firmware, hardware

Verification method: System test

SRP.02 Water level update rate

The water level shall be updated at least every hour.

Acceptance critiera:

  • During a 24 hour period, at least 95% of expected number of samples are logged.
  • Received samples are timestamped.

Source: UN.1

Design outputs: Firmware

Verification method: System test. Logs are inspected for timestamp data.

SRP.03 Heartbeat reporting

The system shall periodically report heartbeat data to the remote service.

Acceptance critera:

  • Heartbeat data contain lowest battery level recorded.
  • Heartbeat data contain percent of time powered by solar
  • Heartbeat data contain sampling failure rate (%)

Source: UN.2

Design output: Firmware, software

Verification method: Inspection, System test

SRP.04 Alive indication

The sensing unit of the system shall provide means to a user to check that it is currently operational and that there are no errors.

Acceptance critera:

  • A visual indicator is enabled when there is no error.
  • A visual indicator is enabled when there is an error.
  • The indicators are not visible at the same time.

Source: UN.2

Design output: Firmware, hardware

Verification method: System test

SRP.05 Data retention period

The system shall retain data for at least 30 days.

Acceptance criteria:

  • After leaving the system on for 40 days, the oldest timestamp is at least 30 days old.

Source: UN.1

Design output: Software

Verification method: System test. Leave system on for 40 days and inspect storage file/database.

Security requirements

SRS.01 Authentication

Sensing unit and remote service shall mutually authenticate before transmitting data.

Acceptance critiera:

  • Remote service rejects data from sensing device that fails authentication.
  • Sensing unit does not upload data to service with no or failed authentication.
  • Authentication failure is treated as connection error.

Source: UN.5

Design ouput: Firmware, software

Verification method: System test.

Environmental requirements

SRE.01 IP classification

The system shall withstand rain and dust and expected outdoor temperatures.

Acceptance critera:

  • IP54.

Source: UN.4

Design output: Mechanics

Verification method: System test.

SRE.02 Operating temperature and humidity

The system shall be able to operate in spring, summer and fall conditions, in the southern of Sweden.

Acceptance critera:

  • The system measures and transmits data at 5-40ºC.

Source: UN.4

Design output: Mechanics, Hardware

Verification method: System test.

Functional requirements

SRF.01 Read water level

It shall be possible to read the latest measured water level from the remote service. Time or age of the reported value shall be presented.

Acceptance critera:

  • The latest measurement is displayed when accessing the remote service.
  • The timestamp is presented with value.

Source: UN.1

Design output: Firmware, software

Verification method: System test.

SRF.02 Self-powered

The system shall be self-powered. (Solar charging and battery)

Acceptance critera:

  • The system shall manage at least 4 days of heavy clouds, with 1 hour per day of full sunlight.
  • No charging with wire is required during the period.

Source: UN.3

Design output: Hardware

Verification method: Inspection and analysis. (Measure current consumption in different conditions and compare with battery capacity)

SRF.03 Data buffering

In case of no connection to remote service, data shall be buffered for 1 day.

Acceptance criteria:

  • At least 24 hours worth of data shall be transmitted upon restored connection, if lost for at least 24h.
  • If local buffer is full, the oldest data shall be discarded first.
  • Already transmitted data is not retransmitted.

Source: UN.2

Design output: Firmware

Verification method: System test. (Remove remote service or WiFi for >24 hours, check uploaded data. Check for duplicates after another 24 hours)

Interface requirements

SRI.01 WiFi connectability

The sensing unit shall connect to the remote service using WiFi.

Acceptance critera:

  • WiFi is used to transmit data.

Source: UN.2

Design output: Firmware, hardware

Verification method: Inspection. Check documentation.