Abstract: A magnetic flowmeter includes circuitry for applying a first relatively high voltage across the electromagnet coils of the meter for a controlled length of time to build the coil current to a desired level and circuitry for applying a second, relatively low voltage across the electromagnet coils after the application of the high voltage to maintain the coil current at the desired level. The coil current is sampled at predetermined times during the application of the relatively low voltage and the length of time the relatively high voltage is applied is varied to eliminate differences in consecutive coil current samples. The actual level of the coil current is controlled by a magnetic amplifier which includes a saturable reactor. The voltage waveform applied to the electromagnetic coil reverses in polarity each half cycle due to a bridge circuit which is connected to a power supply of a single polarity.

Abstract: An isolation amplifier especially suited for magnetic flowmeters includes circuitry for converting an analog input signal to a duty cycle imposed upon a digital waveform, including generating clock pulses for synchronizing the digital waveform. Low-cost opto-couplers are provided for optically transmitting the digital waveform and information representative of the clock pulses across a barrier which would degrade the analog input signal and for receiving the optically transmitted digital waveform and clock pulse information and recreating the digital waveform with imposed duty cycle therefrom. Circuitry for digitally ranging the duty-cycle signal before the analog signal is reconstructed is also disclosed.

Abstract: An override process control system for regulating a process with a single final control element, such as a valve, from two or more process variables that are interdependent and must not exceed acceptable minimum and maximum limits. The system includes a like number of electronic controllers each acting to compare a respective process variable with a set point to produce an output signal reflecting the deviation of the process variable from the set point. The primary controller responsive to the process variable directly influenced by the setting of the final control element has its output signal applied thereto to regulate this element, whereas the other controllers which are responsive to secondary process variables operate on a standby basis.