Loop-powered field device with improved loop current control

A field device for determining a process variable and providing the process variable to a remote location via a two-wire current loop, the field device comprising:

• a first loop terminal and a second loop terminal for connection of the field device to the two-wire current loop in such a way that a loop current flows through an electric circuit of the field device from the first loop terminal to the second loop terminal;
• a measurement unit for determining the process variable using energy received via the two-wire current loop for operation of the measurement unit;
• a loop current control device for controlling the loop current to encode the process variable determined by the measurement unit, the loop current control device being provided in the electric circuit between the first loop terminal and a first node of the electric circuit;
• an asymmetrically conducting device provided in the electric circuit between the first node of the electric circuit and a second node of the electric circuit, the asymmetrically conducting device being configured to allow current to flow through the asymmetrically conducting device from the first node towards the second node when a potential at the first node is higher than a potential at the second node, and to substantially prevent current to flow through the asymmetrically conducting device from the second node towards the first node when the potential at the second node is higher than the potential at the first node;
• an energy storage device for storing energy received via the two-wire current loop, the energy storage device being provided in the electric circuit between the second node of the electric circuit and the second loop terminal;
• and
• a controllable shunt regulator provided in the electric circuit between the first node of the electric circuit and the second loop terminal, in parallel with the energy storage device and the asymmetrically conducting device,
• wherein the measurement unit is provided in the electric circuit between the second node of the electric circuit and the second loop terminal in parallel with the energy storage device.