Digitally compensated hydraulic scale system

A weighing system which comprises:

• a weighing platform or structure;
• a plurality of hydraulic transducers positioned for measuring the load applied to the weighing platform or structure, each hydraulic transducer generating a hydraulic fluid output at a pressure proportional to the load applied to the hydraulic transducer;
• a pre-calibrated pressure transducer module which comprises:
• i) a base plate comprising a plurality of cavities;
• ii) at least one diaphragm plate sealingly covering the cavities, each hydraulic transducer fluid output being connected to an associated cavity of the pressure transducer module, the diaphragm plate over each cavity deforming generally proportionately to variations in the pressure of the hydraulic fluid in that cavity;
• iii) a sensor associated with each cavity for generating an output signal representative of the deformation of the diaphragm plate over that cavity, the sensor comprising strain gauges arranged in a wheatstone bridge, each sensor located adjacent to its associated cavity on the other side of the diaphragm plate from the cavity;
• and
• iv) a temperature sensor for generating a temperature output signal representative of the temperature of the pressure module;
• multiplexor/convertor means for multiplexing the sensor output signals and the temperature output signal into a digital data stream;
• calibration data storage means for storing pre-calibration data for the pressure transducer module;
• and
• a controller for receiving the digital data stream and for applying the calibration data to calculate the pressure of the hydraulic fluid in each cavity.

A modular hydraulic weighing system having a plurality of hydraulic transducers for measuring a load applied to a weighing platform or structure, each hydraulic transducer generating a hydraulic fluid output at a pressure proportional to the load applied to the hydraulic transducer, the modular hydraulic weighing system comprising:

• a pressure transducer module which comprises a plurality of pre-calibrated pressure transducers, each pre-calibrated transducer comprising input connection means to a hydraulic transducer output having a fixed pre-determined output pressure range corresponding to the load range for that hydraulic transducer, each pressure transducer generating an uncompensated output signal corresponding to the pressure of the input to the pressure transducer;
• and
• a controller which comprises stored calibration data for each pre-calibrated pressure transducer, means for receiving the output of each pressure transducer, means for applying the calibration data for each pressure transducer to the output of that pressure transducer to calculate the pressure of the output of that pressure transducer to calculate the transducer of the input to that pressure transducer, means for inputting the load range of each hydraulic transducer, and means for determining the load on each hydraulic transducer by scaling the pressure input to each pressure transducer against the load range of its associated hydraulic transducer;
• whereby the pressure transducer module and controller may be used with hydraulic transducers having different load ranges.

A weighing system which comprises:

• a weighing platform or structure;
• a plurality of hydraulic transducers positioned relative to the platform or structure for measuring a load applied to the platform or structure, each hydraulic transducer generating a hydraulic fluid output at a pressure proportional to the load applied to the hydraulic transducer;
• a pressure transducer module which comprises a plurality of pre-calibrated pressure transducers, the pressure transducer module comprising i) a base plate comprising a plurality of cavities, each cavity in fluid communication with the hydraulic fluid output of an associated hydraulic transducer, ii) at least one diaphragm plate covering the cavities, the diaphragm plate deforming generally proportionately to variations in the pressure of the hydraulic fluid in the cavities, and iii) a sensor associated with each cavity for generating an uncompensated output signal corresponding to the pressure of the output of the hydraulic transducer associated with such cavity;
• and
• a controller which comprises stored calibration data for each sensor, means for receiving the output of each sensor, and means for applying the calibration data for each sensor to the output of that sensor to calculate the load on the hydraulic transducer associated with that sensor.

An improved weighing system having a plurality of hydraulic transducers for receiving an applied load, each generating a pressurized hydraulic fluid output, a pressure transducer module for receiving the pressurized hydraulic fluid outputs and for generating pressure output signals each corresponding to the pressure of the hydraulic fluid output of a hydraulic transducer, and a weighing system controller for reading the pressure output signals and for generating a load signal corresponding to the magnitude of the applied load;

• the improvement comprising:
• the pressure transducer pressure output signals being variable according to a predetermined response characteristic relating the output signals to creep, hysteresis, non-linearity and temperature properties for the pressure transducer module;
• means for storing calibration data for the pressure transducer module, the calibration data corresponding to the predetermined response characteristic;
• the weighing system controller further comprising means for retrieving the calibration data and utilizing the calibration data for providing error and calibration correction to the pressure transducer module output signals for generating an error corrected load signal.

An improved method of performing cornering error correction in a scale having a plurality of hydraulic transducers for receiving a load applied to the scale, each hydraulic transducer generating an output signal corresponding to the magnitude of the load on that hydraulic transducer, and means for reading each output signal, for converting the output signal to a digital signal and for generating a digital load signal corresponding to the magnitude of the total applied load;

• wherein the improvement comprises:
• applying a known weight to each hydraulic transducer on the scale;
• reading the output signal of each hydraulic transducer and converting the output signal to a digital output signal;
• comparing the digital output signal of each hydraulic transducer to an expected digital output value corresponding to the known weight and determining a span correction factor for each hydraulic transducer, whereby each hydraulic transducer output signal may be corrected to correspond to the expected output value;
• storing the span correction factor for each hydraulic transducer;
• and
• retrieving the span correction factor for each hydraulic transducer when a load is applied to the scale and applying the span correction factor for each hydraulic transducer to the digital output signal for that hydraulic transducer for providing cornering error correction to the output signals, and generating an error corrected load signal.

A system for calibrating a pressure transducer which comprises:

• a calibration chamber;
• means for applying a varying pressure to the pressure transducer in the calibration chamber, the pressure transducer generating an output related to the magnitude of the pressure and error factors according to a determinable response characteristic;
• a calibration controller for controllably varying the pressure on the hydraulic transducer and reading the output of the pressure transducer at the varying pressure;
• reference pressure measuring means for generating a pressure reference output corresponding to the magnitude of the pressure applied to the pressure transducer;
• the calibration controller further comprising means for reading the pressure reference output and generating calibration data corresponding to the response characteristic;
• and
• means for storing the response characteristic data.

An improved hydraulic load cell that generates a hydraulic fluid output at a pressure proportional to a load applied to the hydraulic transducer, the hydraulic load cell having a housing, the improvement comprising:

• a pre-calibrated pressure transducer located within the housing that generates an uncompensated output signal representative of the pressure of the hydraulic fluid output;
• calibration data storage means located within the housing for storing pre-calibration data for the pressure transducer;
• and
• a controller located within the housing for receiving the output signal and for applying the calibration data to calculate the load on the hydraulic load cell.