Athermal hung mass accelerometer with reduced sensitivity to longitudinal temperature gradients

A hung mass accelerometer, comprising:

• a body having an internal cavity oriented along a longitudinal axis, said body formed of one or more materials having an effective body coefficient of thermal expansion (CTE);
• first and second flexures attached to the body at opposite ends of the internal cavity, said first and second flexures compliant along the longitudinal axis;
• a proof mass between the first and second flexures to hang inside the internal cavity, said proof mass allowed to move along the longitudinal axis in an open-loop configuration;
• first and second sensor heads mounted on the body on oppose ends of the internal cavity along the longitudinal axis on opposite sides of the proof mass at distances d1 and d2 that increase and decrease in opposition as said proof mass moves along the longitudinal axis, each said sensor head having a reference coil responsive to an alternating drive signal to produce an oscillating primary magnetic field that induces Eddy currents in the proof mass that create an opposing secondary magnetic field that resists the primary magnetic field generated by the reference coil, any change in the distance between the reference coil and the proof mass causing a change in the magnetic field interaction that produces differential alterations to the alternating drive signal,
• said first and second sensor heads formed of one or more materials having effective first and second sensors CTEs of 60-80% of the body CTE to approximately null the effects on the alternating drive signal of a body temperature gradient along the longitudinal axis.

A hung mass accelerometer, comprising:

• a body having an internal cavity oriented along a longitudinal axis, said body formed of one or more materials having an effective body coefficient of thermal expansion (CTE);
• first and second flexures attached to the body at opposite ends of the internal cavity, said first and second flexures compliant along the longitudinal axis;
• a proof mass between the first and second flexures to hang inside the internal cavity, said proof mass allowed to move along the longitudinal axis in an open-loop configuration, wherein said body, said first and second flexures and said proof mass are integrally formed from a single piece of metal of either titanium or stainless steel;
• first and second sensor heads mounted on the body on oppose ends of the internal cavity along the longitudinal axis on opposite sides of the proof mass at distances d1 and d2 that increase and decrease in opposition as said proof mass moves along the longitudinal axis, each said sensor head having a reference coil responsive to an alternating drive signal to produce an oscillating primary magnetic field that induces Eddy currents in the proof mass that create an opposing secondary magnetic field that resists the primary magnetic field generated by the reference coil, any change in the distance between the reference coil and the proof mass causing a change in the magnetic field interaction that produces differential alterations to the alternating drive signal,
• said sensor heads having a length LS measure from an attachment point of the sensor head to the body that is between one-half a body length LB and a full body length measured from the attachment point to a center line of the proof mass;
• said first and second flexures configured to substantially thermally isolate the proof mass from the body;
• said first and second sensor heads formed of one or more materials having effective first and second sensors CTEs of 60-80% of the body CTE such that the growth of said first and second sensor heads along the longitudinal axis is approximately equal and opposite the growth of said body along the longitudinal axis in response to a predicted body temperature gradient along the longitudinal axis to approximately null the effects on the alternating drive signal.