Vibrating fork type field device with coil arrangement to induce vibration

A field device for determining a change in a property of a medium, the field device comprising:

• first and second tines to be arranged in the medium;
• first and second rods coupled to the first and second tines, in such a way that vibration of the first rod in relation to the second rod results in vibration of the first tine in relation to the second tine;
• a coil arrangement fixed to the first rod;
• a magnet fixed to the second rod, opposite the coil arrangement;
• excitation circuitry coupled to the coil arrangement and controllable to provide a time-varying current to the coil arrangement, resulting in vibration of the first tine in relation to the second tine;
• sensing circuitry coupled to the coil arrangement and configured to provide a sensing signal indicative of a change in at least one property of the vibration of the first tine in relation to the second tine;
• and
• measurement control circuitry coupled to the excitation circuitry and the sensing circuitry, and configured to:
• control the excitation circuitry to provide the time-varying current to the coil arrangement;
• receive the sensing signal from the sensing circuitry;
• and
• determine the change in the property of the medium based on the change in the at least one property of the vibration and a predetermined relation between the change in the at least one property of the vibration, and the change in the property of the medium, wherein:
• the field device comprises a housing;
• the first and second rods, the excitation circuitry, and the sensing circuitry are enclosed by the housing;
• and
• the first and second tines are arranged outside the housing, wherein:
• the housing comprises a membrane;
• and
• the first and second rods are coupled to the first and second tines via the membrane.

A field device for determining a change in a property of a medium, the field device comprising:

• first and second tines to be arranged in the medium;
• first and second rods coupled to the first and second tines, in such a way that vibration of the first rod in relation to the second rod results in vibration of the first tine in relation to the second tine;
• a coil arrangement fixed to the first rod;
• a magnet fixed to the second rod, opposite the coil arrangement;
• excitation circuitry coupled to the coil arrangement and controllable to provide a time-varying current to the coil arrangement, resulting in vibration of the first tine in relation to the second tine;
• sensing circuitry coupled to the coil arrangement and configured to provide a sensing signal indicative of a change in at least one property of the vibration of the first tine in relation to the second tine;
• and
• measurement control circuitry coupled to the excitation circuitry and the sensing circuitry, and configured to:
• control the excitation circuitry to provide the time-varying current to the coil arrangement;
• receive the sensing signal from the sensing circuitry;
• and
• determine the change in the property of the medium based on the change in the at least one property of the vibration and a predetermined relation between the change in the at least one property of the vibration, and the change in the property of the medium, wherein:
• the coil arrangement comprises a first coil fixed to the first rod and a second coil fixed to the first rod;
• the excitation circuitry is coupled to the first coil;
• and
• the sensing circuitry is coupled to the second coil.

A field device for determining a change in a property of a medium, the field device comprising:

• first and second tines to be arranged in the medium;
• first and second rods coupled to the first and second tines, in such a way that vibration of the first rod in relation to the second rod results in vibration of the first tine in relation to the second tine;
• a coil arrangement fixed to the first rod;
• a magnet fixed to the second rod, opposite the coil arrangement;
• excitation circuitry coupled to the coil arrangement and controllable to provide a time-varying current to the coil arrangement, resulting in vibration of the first tine in relation to the second tine;
• sensing circuitry coupled to the coil arrangement and configured to provide a sensing signal indicative of a change in at least one property of the vibration of the first tine in relation to the second tine;
• and
• measurement control circuitry coupled to the excitation circuitry and the sensing circuitry, and configured to:
• control the excitation circuitry to provide the time-varying current to the coil arrangement;
• receive the sensing signal from the sensing circuitry;
• and
• determine the change in the property of the medium based on the change in the at least one property of the vibration and a predetermined relation between the change in the at least one property of the vibration, and the change in the property of the medium, wherein:
• the coil arrangement comprises a single coil fixed to the first rod;
• the excitation circuitry is coupled to the single coil and configured to provide a multi-frequency excitation signal to the single coil;
• and
• the sensing circuitry is coupled to the single coil and configured to sense a frequency-dependent impedance of the single coil.