Analogue computer for solving polynomial equations

A gas density calculator comprising a pressure sensor for providing an analogue signal representative of the pressure of a gas of which the density is to be calculated, a temperature sensor for providing an analogue signal representative of the temperature of the gas, a high gain comparator means operative to provide a common multiplier signal dependent on the respective difference between a composite signal and a zero reference level;

• two chains each of three multiplication modules, each module being responsive to said common multiplier signal to provide a respective analogue output signal which is representative of the product of the magnitude of a respective analogue input signal to the module and the factor represented by said common multiplier signal, the input signals of the second and third modules in each chain being supplied by the output signals of the first and second modules respectively of the respective chain, the input signal of the first module in one chain being a constant reference signal and that of the first module in the other chain being provided by said gas temperature signal, means for combining the output signals of all said modules together with said gas pressure signal to provide said composite signal so as to be representative of the polynominal expression of the equation, the composite signal being a negative feed back signal to the comparator means and the gain of the comparator means being such that the computer is operative to maintain said composite signal substantially equal to said zero reference level.