Abstract: An analog to digital converter uses an integrator having an input to which is applied the unknown voltage to be converted. An opposing reference voltage is switched by a switch means between positive and negative levels to cause the integrator output to ramp up and down between two levels to produce a periodic sawtooth waveform. The sawtooth waveform is applied to a hysteresis comparator which changes its output state when the sawtooth wave form magnitude equals the upper and lower hyteresis levels of the comparator. The output of the comparator is arranged to trigger an edge-sensitive "D" flip-flop. A fixed frequency clock signal from a clock signal source is applied to a clock input of the flip-flop to switch the flip-flop in combination with the output from the comparator. An output signal from one side of the flip-flop is applied as an actuating signal to the switch means to switch the reference signal level.

Abstract: A method of measuring the specific gravity of a fluid to be analyzed includes the steps of pressurizing a fixed volume chamber by the fluid to be analyzed, allowing the pressure in the chamber to decay through a fixed restriction between predetermined pressure limits, measuring the time interval of the pressure decay between the pressure limits and converting the time interval value to the specific gravity of the fluid to be analyzed.

Abstract: A calorific content analyzer for determining the calorific content of a combustible gas while compensating the analysis of the calorific content for fuel entrained oxygen. The gas is combusted to achieve substantially stoichiometric combustion by varying the air/fuel ratio supplied to a combustion chamber by a rotary valve which is speed controlled in response to a sensing of oxygen in the combustion products. A first measurement of the calorific content of the fuel gas is made using a normal operation of the analyzer and a second measurement is made using a known amount of air added by the rotary valve to the combustible gas stream. The true air/fuel ratio and the calorific content of the fuel gas is then computed using a predetermined relationship among the system variables.

Abstract: A P-I-D controller in a process control system is self tuned in response to discrete time model identification parameters which are converted to P-I-D form.Additionally, the P-I-D parameters are limited to prevent them from exceeding the controller's specified range.

Abstract: Unwanted bias is eliminated from a process control system by high pass filters which are disposed between the process and the process model.

Abstract: A circuit for preventing data transfers to a RAM by a microprocessor when primary ac power fails also puts the RAM in standby after a period adequate to complete any data transfer started. The sequence is provided by providing a first signal to the microprocessor transfer enable line upon loss of primary power. A second signal is provided for the enable line of the RAM after a predetermined delay but before decay of the dc power to the RAM.