Hybrid power module with fault detection

A method for providing and monitoring power for a wireless field device, the method comprising:

• connecting a power module so as to provide power to the wireless field device, the power module comprising an energy storage device and a local power source connection;
• powering the wireless field device primarily using power from the local power source connection;
• powering the wireless field device supplementally using power from the energy storage device, when power from the local power source is unavailable or insufficient to power the wireless field device;
• setting a fault signal value of a process signal based on voltage supplied by the power module;
• reporting a fault with the local power source if the fault signal value falls within a first range;
• and
• reporting a fault with the energy storage device if the fault signal value falls within a second range.

A wireless field device assembly comprising:

• a process sensor configured to monitor a process variable;
• a housing enclosing an interior space;
• a cover defining a receptacle between the housing and the cover;
• a power module configured to fit removably inside the receptacle and power at least a subset of the wireless device assembly;
• an energy storage device inside or affixed to the power module, and located within the receptacle;
• a local power source electrically connected to the power module;
• a processor located within the interior space and configured to produce:
• a process variable signal reflecting the process variable monitored by the industrial process sensor;
• and
• a fault signal value that distinguishes between energy storage device faults, local power source faults, and no-fault states based on voltage at the power module.