Abstract: A servo-system includes a high-gain direct-coupled direct current (dc) differential amplifier to which a dc input signal is fed. An adder adds the dc amplifier output to a comparison voltage, and the adder output is applied through a filter circuit to a second input of the differential dc amplifier. A servo-amplifier drives a servo-motor in accordance with the dc amplifier output. Means are provided for zero-balancing the dc amplifier output while varying the comparison voltage by the servo-motor.

Abstract: A servo-system is provided for self-balancing systems using an ac servomotor capable of maintaining loop gain substantially constant irrespective of span adjustment and without capacitor coupling. It includes a direct-coupling dc amplifier for comparing input and comparison signals and amplifying the result, a servo amplifier having a differential direct-coupling amplifier with inverting and non-inverting input terminals, with feedback from its output to the inverting input terminal and a switch to the non-inverting input terminal operating at the same frequency as the ac power source for the servomotor, to maintain the loop gain constant irrespective of span adjustment, and means causing the ac servomotor to move a slide resistor to bring the compared signal into balance with the input signal.Provision is also made for receiving input signals from thermoelectric or resistance thermometers and balancing the system using these signals.

Abstract: A simplified, compact, inexpensive portable self-balancing recorder to be used in the monitoring of data relating to pollution and/or environmental protection. The recorder is about 650 cubic centimeters in volume and weighs about 5 kilograms; it comprises a minimal number of constitutent components and may be operated without certain costly options (e.g. alarms and controls) if desired. The recorder uses printed circuit board circuitry to monitor and process input signals from the measuring points, and these components can conveniently and easily be removed from the recorder for adjustments or replacements. The recorder includes means for adjusting the ink pressure according to recording conditions and provides an inking system with an hermetically sealed pen point to prevent introduction of bubbles into the ink.

Abstract: A multipoint recorder of the type used to monitor a number of measuring instruments and including a mechanism having a group of contacts for sequentially selecting signals from a number of measuring points, a self-balancing circuit having a balancing motor for intermittently measuring each of said signals, and an indicating and recording mechanism operated in synchronism with said selection mechanism for indicating and recording, e.g., on a strip chart, the group of measurements supplied by said self-balancing circuit. The multipoint recorder is characterized by a group of auxiliary contacts in said selection mechanism interspersed with the group of measuring point selection contacts, said auxiliary contacts being switched with a given delay behind switching of the measuring point selection contacts so that the auxiliary contacts are sequentially closed as the selection mechanism switches between measuring point selection contacts.