Leeds & Northrup Company

General Signal Corporation

George C Mergner

James J Hitt

Herman W Levin

Peter J Clack

There is provided a differential amplifier having a plurality of inputs connected through input resistors to a summing junction at the inverting input of a differential amplifier which also has a negative feedback path having a feedback resistor. One of the input resistors is connected to the output signal of the primary element or transducer. A second of the input resistors is connected to a zero compensating signal which varies with changes in the temperature of the transducer from a certain value at a reference temperature. A third input resistor is connected to a fixed signal of a value which is adjusted to correspond to the certain value of the compensating signal at the reference temperature but of opposite polarity so as to tend to cancel the compensating signal when the transducer is at the reference temperature. The combination of the three inputs then produces an output from the differential amplifier corrected for changes in the zero of the measurement due to temperature changes.

Temperature compensation for zero and span changes in a measurement

The displacement of the diaphragm in a differential pressure sensor of the differential capacitor type produces an output signal substantially linearly related to the displacement. The capacitors are charged in parallel from a constant current source for a fixed period of time and discharged through separate discharge circuits for another fixed period of time. An integrating differential amplifier connected to the two capacitors as they discharge produces an output signal related to the area between the two discharge curves which is substantially linearly related to the extent of displacement of the diaphragm of the differential pressure sensor. The output from the amplifier is used to control the current output from the device.

Differential capacitance measuring circuit

A flow-through thermal detector for determining the temperature change resulting from a reaction in a fluid stream includes a pair of parallel fluid paths one of which carries the fluid stream in which the reaction occurs while the other carries a similar fluid without the occurrence of a reaction. The detector includes a temperature sensor for each path. The first of the sensors is mounted to sense the temperature of the reacting stream after said reaction has occurred while the second of the sensors is mounted to sense the temperature of the non-reacting stream at a point in its flow path comparable to that at which the first sensor is mounted. A heat shield is provided surrounding the parallel paths and the heat shield is controllable to a predetermined temperature. Preheating of the streams is carried out by a preheating means positioned within the heat shield to receive the fluid stream entering the shield. The preheating means is controlled to bring the fluid streams of the parallel paths to the same predetermined temperature to which the heat shield is controlled. The streams then enter an equalizing means surrounding that part of the paths between the preheating means and the region in which the reaction occurs for equalizing the temperatures of the streams in the parallel paths prior to the streams reaching the reaction region.

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Glenside, PA, United States of America

George C Mergner