Design Specifications

These design specifications come after a second meeting with Geoforce and after considering the end user applications. They are based on and expand the level 1 requirements set forth at the beginning of this project. As this device is to communicate with Geoforce’s transmitter, specific protocols will need to be followed. The level one requirement for this is to communicate via I2C. However, if possible, multiple devices should communicate with a single Geoforce transmitter via Bluetooth Low Energy (BLE).

Digitize 4-20mA Loop Sensor Data

  • Digitize data with 10 bit accuracy across 0 to 25mA
  • Convert current to voltage
  • Match connection impedance with impedance of twisted pair

Run on 4 Lithium Primary Cells

  • Run on cells 3.6v each
  • Transmit 2 measurements per day
  • Last for 5 years without replacement

Interface with Geoforce Transmitter

  • Communicate via I2C
  • Format data into a 16 bit packet
    • 10 bits reserved for sensor data
    • Use remaining 6 bits for appropriate data

Fault Detection

  • Include fault code in transmission
  • Detect device specific faults
  • Detect sensor faults
    • Disconnected / line cut
    • Undercurrent
    • Overcurrent

Additional Specifications

  • Transmit sensor data with less than 5% error
  • Fit inside the volume of Geoforce's GT1 transmitter
  • Cost less than $50 to build at a quantity of 10,000

EELE 488