Weight-sensor calibration for gravimetric coal feeder

A device for selectively applying a test load to a weight-sensing mechanism in an enclosed conveyor unit for feeding material at a controlled rate, said weight-sensing mechanism including means for continuously sensing the weight of a variable quantity of material being conveyed through a predetermined reference zone and load cell means for generating a voltage signal representative of the weight sensed by said means, said device comprising

• a calibrating weight,
• a control shaft journaled in said conveyor unit and having its axis transverse to the direction of feed,
• a pair of circular eccentric members mounted on said shaft at spaced locations from and coaxial with one another on opposite ends of said shaft and with their common axis of eccentricity offset from the axis of said shaft,
• a pair of vertical support rods one being operatively connected to one of said eccentric members and the other being operatively connected to the other of said eccentric members, said calibrating weight being adapted to be supported by and between said support rods,
• means for rotating said shaft between a first position wherein the axis of eccentricity of said eccentric members is above the axis of said shaft and a second position wherein the axis of eccentricity of said eccentric members is below the axis of said shaft whereby when said shaft is in said first position said calibrating weight is supported by said rods and when said shaft is in said second position said calibrating weight is lowered by said rods and the weight thereof is transferred to said weight-sensing mechanism.

In a gravimetric feeder having a belt conveyor for conveying particulate material to a delivery zone, said conveyor embodying a weighing span supported by a plurality of rollers, one of said rollers being a weighing roller, said weighing roller being supported by a weight sensing mechanism embodying load cells adapted to generate a signal representative of the weight supported by said weighing roller, the improvement which comprises a device for selectively applying a test load to said weight sensing mechanism comprising:

• a calibrating weight;
• a control shaft located above said weight sensing mechanism;
• vertical support means operatively connected to said control shaft at its upper end and to said calibrating weight at its lower end;
• and
• means for rotating said shaft about its axis between one position wherein the weight of said calibrating weight is transferred to said weight sensing mechanism when it is desired to calibrate said weight sensing mechanism and another position wherein said calibrating weight is supported by said vertical support means for supporting said calibrating weight independently of said weight sensing mechanism during normal operation of said feeder.