7. CONCLUSIONS

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This work has presented a new method of compensation of temperature errors in semiconductor pressure transducers.
The method consists in carrying out the nulling of the temperature error of the transducer at a certain number of discrete temperatures. This nulling brings the temperature error of the transducer identically to zero over the whole operating temperature range, independently of the choice of the values of the compensation temperatures, in the case of complete temperature compensation, and makes possible a considerable reduction of the value of the temperature error in the case of incomplete compensation.
The method is characterized by the use of only one element realizing the nulling of the temperature error for each selected compensation temperature and for each compensated parameter (zero, span) of the transfer characteristic of the transducer. What is required of such elements is the realization of the division of the compensating signal. The signals present on such elements are therefore equal to the temperature errors compensated by them, that is, small fractions of the measuring range, as a result of which the requirements on their absolute stability are lowered. This makes it possible, in the compensation process, to place these adjusting elements outside the temperature chamber, by which directness and ease of compensation are achieved.¹

The theoretical analysis carried out has shown the possibility of obtaining complete compensation in the case where the number of compensation temperatures is equal to the degree of the polynomial describing the temperature error of the sensor parameter under consideration. It has also been proved that complete compensation can also be obtained with a reduced number of temperatures if certain properties of the function approximating the temperature error of the sensor are known in advance.
Incomplete compensation has been analysed for the cases most often encountered in practice, namely for the case of a quadratic and of a cubic function describing the temperature error of the compensated sensor parameter.
A general design of a circuit realizing the method has been proposed in

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the form of a multiple bridge. The triple bridge circuit has been considered in more detail. The problem of the interaction between the temperature compensation of the lower and upper range values of the measuring range has been discussed. A detailed design of a circuit realizing the method has been presented on the example of a piezoresistive pressure transducer. A design outline of the more interesting subassemblies of the transducer connected with the compensation circuit has been presented. A statistical analysis of the maximum errors of the sensor has been discussed with a view to the choice of the degree of the polynomial describing the compensating signal. Computer programs optimizing the characteristics of the single bridges compensating the zero drift and span drift of the transducer have been presented. On the basis of the results of these programs the optimum difference between the reference temperature and the compensation temperature has also been determined. The temperature compensation procedure of the transducer has been discussed. The results of tests of the prototypes, fully confirming the effectiveness of the new method, have been included.
A particular advantage of the new method is the unidirectional independence of the settings of the elements nulling the temperature error. This independence consists in the fact that adjustment at a given temperature does not make it necessary to change the settings of the elements adjusted at the preceding temperatures. This eliminates the need for iterative determination or calculation of the final settings of these elements. This property is particularly valuable under the conditions of industrial series production of transducers, since the adjustment can be carried out quickly by staff without high qualifications.

In the proposed circuit design of the method, independence is obtained between the conditions ensuring compensation of the lower range value and the conditions ensuring compensation of the upper range value of the measuring range.
The method presented in this work is at present being introduced into series production at the Mera-Pnefal Industrial Automation Enterprise, and in 1978 the manufacture of 1000 units of transducers using the method is planned. The introduction of the new method eliminates the time-consuming

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and laborious process of selecting the values of, and winding, the copper and manganin compensation resistors that was used in the old product, at the same time shortening by approx. 80 % the time needed to carry out the compensation. The new method is characterized by universality of application. It may be applied to the compensation of the temperature errors of any transducers for non-electrical quantities having a linear transfer characteristic and a temperature error additive to the value of the measured signal. In such cases only the detailed circuit design is subject to modification. The method may also find application in the compensation of the effect of temperature in measuring instruments other than transducers for non-electrical quantities, e.g. in instrumentation amplifiers, analog-to-digital converters, generators, etc. The method moreover makes possible the compensation of the effect of quantities other than temperature, for example giving the possibility of compensating the effect of pressure in a temperature transducer.
On the basis of the theoretical analysis carried out in this work and of the experimental results obtained, it appears that the thesis stated at the outset has been fully proved.