Method and apparatus for driving an air core gage

The method of driving a gage to indicate a value proportional to the magnitude of an input quantity wherein the gage is of the type having first and second coils in quadrature to establish a resultant magnetic field and a pointer angularly positioned by the resultant field comprising the steps of,

• providing a varying current which varies with the input quantity as the tangent of an angle in the range of 0.degree. to 45.degree. over each of a plurality of gage octants,
• providing a reference current having a value equal to the maximum value of the said varying current,
• applying the reference current in a first polarity to the first coil and the varying current in a first polarity to the second coil when the input quantity is in a first range whereby the pointer angle varies throughout a first octant of the gage as the input quantity varies throughout the one range,
• applying the reference current in the first polarity to the first coil and the varying current in a second polarity to the second coil when the input quantity is in a second range adjacent the first whereby the pointer angle varies throughout a second octant of the gage as the input quantity varies throughout a second range adjacent the said one range,
• applying the reference current in the second polarity to the second coil and the varying current in a first polarity and then a second polarity to the first coil when the input quantity varies throughout respective third and fourth ranges whereby the pointer angle quantity varies throughout third and fourth octants of the gage, and then
• for subsequent change of the input quantity through further ranges continuing the pattern of alternately applying the reference and variable currents to the respective coils and progressively varying the variable current from maximum value in one polarity and through 0 to maximum value in the other polarity for each pair of octants to progressively change the direction of the pointer angle proportional to changes in the input quantity.

Apparatus for driving a gage to indicate a value proportional to the magnitude of an input quantity wherein the gage has first and second coils in quadrature to establish a resultant magnetic field and a pointer angularly positioned by the resultant field, comprising

• a circuit responsive to the input quantity to generate a binary number proportional to the magnitude of the quantity, the binary number comprising a set of most significant bits changing in value stepwise as the said magnitude increases and a set of least significant bits changing in a repetitive pattern as the said magnitude increases,
• a memory addressed by the set of least significant bits for storing a table of numbers representing the tangent of an angle represented by the set of least significant bits to provide a binary output,
• a circuit responsive to the binary output for producing a varying signal proportional to the tangent of the angle represented by the set of least significant bits,
• and a steering logic and drive circuit controlled by the varying signal and by the set of most significant bits for producing a variable drive current proportional to the varying signal and a reference drive current equal to the maximum value of the variable drive current, and for selectively applying the two drive currents to the two coils respectively and for controlling the polarity thereof to establish a resultant magnetic field in a direction to position the pointer according to the magnitude of the input quantity.