Automatic weight switching mechanism for substitution type analytical balances

In an analytical balance for accurately weighing an unknown mass, said balance including a pivotably mounted balance beam having a weigh pan suspended from a gimbal assembly positioned at one end of said beam and a force coil operatively attached at the opposite end of said beam, a feedback device arranged to sense the movement of said beam from a null reference position, and circuit means interconnecting said feedback means with said force coil for applying a current to said force coil to bias the balance beam to the null position, the resultant current applied to the force coil being an indication of an unbalanced force applied to said balance beam, the improvement comprising:

• converting means for deriving a digital signal related to the magnitude of the resultant current applied to said force coil in response to an unknown weight on the weigh pan;
• counter means adapted to receive said digital signal for measuring said digital signal and for producing a count signal related to said digital signal;
• a plurality of substitution weights;
• means removably suspending said substitution weights from said gimbal assembly;
• a plurality of weight lifting means, one weight lifting means being operatively positioned in associated relationship with each substitution weight, each said weight lifting means when electronically energized operatively removing its associated substitution weight from said gimbal assembly;
• and
• driver means adapted to receive said count signal and operative in response thereto for electrically energizing selected ones of said weight lifting means thereby to remove from said gimbal assembly selected ones of the substitution weights.

An analytical balance for accurately weighing an unknown mass, said balance including a pivotably mounted balance beam having a weigh pan suspended from a gimbal assembly positioned at one end of said beam and a force coil operatively attached at the opposite end of said beam, a feedback device arranged to sense the movement of said beam from a null reference position, and circuit means interconnecting said feedback means with said force coil for applying a current to said force coil to bias the balance beam to the null position, the resultant current applied to the force coil being an indication of an unbalanced force applied to said balance beam, the improvement comprising:

• converting means for deriving a digital signal related to the magnitude of the resultant current applied to said force coil in response to an unknown weight on the weigh pan;
• counter means adapted to receive said digital signal for measuring said digital signal and for producing a count signal related to said digital signal;
• a plurality of substitution weights;
• means removably suspending said substitution weights from said gimbal assembly;
• a plurality of weight lifting means, one weight lifting means being operatively positioned in associated relationship with each substitution weight, each said weight lifting means when electrically energized operatively removing its associated substitution weight from said gimbal assembly;
• memory means receptive of said count signal for holding said count signal received;
• display means operatively connected to said memory means and receptive of said count signal held by said memory means, said display means displaying a visual indication related to said count signal in a predetermined manner;
• and
• energizing circuit means operatively connected to energize selected ones of said weight lifting means.