Temperature compensated measuring system

Claim 1

A digital scale with a temperature compensation system, comprising: a scale mechanism, first transducer means for sensing the force on the scale mechanism due to the presence of an object to be weighed and for generating digital force signals indicative thereof, second transducer means adjacent said scale mechanism for sensing the current ambient temperature and for generating digital temperature signals indicative thereof, means for generating a series of data indicative of n predetermined discrete ambient temperatures within an operating range, a set of data indicative of m known weights, where m and n are integers, means for applying said weights to the scale mechanism in a predetermined sequence at each of said ambient temperatures, data storage means for storing the digital force values obtained with each known weight at each discrete temperature, along with the corresponding digital temperature signal value, computer means for obtaining the calibration constants for said scale by using the known weights as the values of W and the corresponding stored digital force values as the values of F to evaluate the expression ##EQU5## at each temperature and solving the resulting n sets of m simultaneous equations for each of the coefficient terms a 1 (T), a 2 (T) . . . a m (T), and then substituting the numerical values of the coefficient terms for each a i (T) in the set of expressions ##EQU6## where k ij are the calibration constants, and substituting the stored corresponding digital temperature signal values for T, and solving each of the resulting m sets of n simultaneous equations for each k ij , said data storage means having means for storing the computer k ij values as a set of m×n calibration constants, means for computing a numerical value indicative of the corrected weight of an unknown object using the formula ##EQU7## by employing the stored calibration constants which are the computer polynomial coefficients within each a i (T) expression, and means for generating an output signal based on the said computer numerical value representing the corrected weight of the object on the scale mechanism whereby the effect of temperature change on the scale mechanism, transducer means and other electrical components of the scale is taken into account.