Field device and functional unit for the field device

A field device comprising:

• a plurality of functional units;
• and
• an energy supply for the field device;
• wherein a sum of the individual energy consumptions of all of the plurality of functional units is greater than a maximum value of energy which is suppliable to the field device from the energy supply;
• wherein at least two functional units of the plurality of functional units are one of assigned and assignable priorities;
• wherein a functional unit with a higher priority influences the energy consumption of a functional unit of the plurality of functional units having a comparatively lower priority such that a total energy consumption from the energy supply by all of the plurality of functional units is not greater than a maximum value of energy which is suppliable to the field device from the energy supply;
• wherein a line to the energy supply thereof is routed through a functional unit having a higher priority, said functional unit having the higher priority comprising a switch arranged in the line or a controllable current-limiting element arranged in the line to influence energy consumption of the functional unit with the lower priority;
• wherein the switch or the controllable current-limiting element is controllable by the functional unit having the higher priority;
• wherein an entire circuitry and logic for influencing the energy supply of functional unit having the lower priority is integrable with the functional unit having the higher priority;
• wherein the functional unit having the higher priority is formed as a functional module which is retrofittable to the field device, is detachably fastened to the field device, is within a respective housing and is further formed as one of (i) a transmitter module, (ii) a display, (iii) a communication module, (iv) a sensor module, (v) a service interface, (vi) a measurement data processing module, (vii) a control module and (vii) a regulator module.