The Foxboro Company

Robert J Robinson

David A Richardson

Apparatus for converting an analog-format electrical signal or quantity (such as the magnitude of an electrical circuit element) into a corresponding pulse-format signal, preferably in the form of a train of periodic pulses the lengths of which are controllable as a percentage of the cyclic period. A pulsed duty-cycle signal is developed in a negative feedback loop around an integrator having an analog-format input signal. The integrator output controls the d-c level of an up-and-down ramp signal which is fed to a comparator to produce pulses during the times the ramp voltage is above (or below) the firing threshold of the comparator. These pulses control a switch between the integrator input and a reference voltage so as to produce a negative feedback signal for the integrator. The negative feedback action controls the d-c level at the integrator ouptut and thereby sets the pulse duty-cycle to a value such that the average signal level through the pulsed switch to the integrator input relates in prescribed fashion to the applied input signal. The duty-cycle signal developed through such feedback action corresponds directly to the magnitude of the applied input signal.

Apparatus for converting analog-format signals to pulse-format signals

A positioning device for controlling a member such as a pen of a chart recorder, wherein the positioning motion is produced by a wire formed of temperature-responsive material (Nitinol) exhibiting a martensitic transformation which contracts the wire when its temperature is increased within a predetermined temperature range, and relaxes the wire when cooled within that range. The wire is maintained under tension by a spring having a negative spring-rate. This spring cooperates with internally generated forces and the elasticity of the wire material to produce contraction/expansion length changes of the wire in response to changes in its temperature. Electrical circuitry for controlling the wire temperature is disclosed, and includes means for inductively developing a frequency-modulated pulse-current through the wire.

Positioning device using negative spring-rate tensioning means

Flow-metering apparatus of the vortex-shedding type wherein an obstruction in a flowing fluid develops a series of vortices which are sensed by a pressure-responsive piezo-electric element to produce an alternating voltage having a frequency corresponding to the fluid flow rate. The piezo-electric voltage signal is processed by electronic circuitry to provide for precise detection of the zero-crossings of the voltage alternations. The resulting frequency signal controls the charge/discharge characteristics of a set of capacitors, with the average charging current corresponding in magnitude to the frequency of vortex shedding. This average current controls an output amplifier in a feedback arrangement to produce a relatively high-powered d-c flow signal over a two-wire transmission line leading to a remote station. In another arrangement, a high-powered pulsating flow signal is developed for transmission over a three-wire transmission line leading to a remote station.

Vortex flow meter transmitter including piezo-electric sensor

A positioning device for controlling a member such as a pen of a chart recorder, wherein the positioning motion is produced by a wire formed of temperature-responsive material (Nitinol) exhibiting a martensitic transformation which contracts the wire when its temperature is increased within a predetermined temperature range, and relaxes the wire when cooled within that range. The wire is maintained under tension by a spring having a negative spring-rate. This spring cooperates with internally-generated forces and the elasticity of the wire material to produce contraction/expansion length changes of the wire in response to changes in its temperature. Electrical circuitry for controlling the wire temperature is disclosed, and includes means for inductively developing a frequency-modulated pulse-current through the wire.

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Lexington, MA, United States of America

Robert J Robinson