Multiplexed autonomous sensors and monitoring system and associated methods

Abstract

A sensor monitoring system and associated methods are provide that preferably include a plurality of sensors connected in parallel across a single pair of wires that include resistances of equal value placed in series between each sensor. This allows each sensor to measure the voltage dropped between itself and the monitoring system to determine its relative placement on the bus to autonomously assign itself a number to delineate to the monitoring system its relative location on the equipment or item being monitored. The sensors modulate their internal resistance to change the current on the bus to transmit their status to the monitoring system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. application Ser. No. 10 / 345,842, filed Jan. 16, 2003, which claims the benefit of U.S. Provisional Application No. 60 / 349,876, filed Jan. 16, 2002, the disclosures of which are hereby incorporated by reference herein in their entireties, and all commonly owned.FIELD OF THE INVENTION [0002] The present invention generally relates to the field of sensor monitoring, and more particularly to a system of interconnecting and monitoring a plurality of sensors with each sensor having autonomous access to a data communication medium independent of other devices. BACKGROUND OF THE INVENTION [0003] Most machinery or industrial equipment employ sensors for status monitoring or control. Usually, the machinery is relatively complex and more than one sensor is employed to sense more than one parameter, event, or situation. These sensors are connected to monitoring circuits and together or in combination form ...

AI Technical Summary

Benefits of technology

"The present invention provides a sensor system that overcomes the noise and uncertainty of digital proximity and encoder sensors. This is achieved by using a specially adapted analog sensor that eliminates large DC offset signals and amplifies the dynamic signal as much as possible to overcome noise. The sensor system uses multiplexed sensors connected in parallel across a single pair of wires, with resistances of equal value placed in series between each sensor to determine their relative placement on the bus to autonomously assign them a unique number to delineate their function. The sensors modulate their internal resistance to change the current on the bus to transmit their status to the monitoring system. The monitoring system uses a series of digital numbers denoting which sensor is to be calibrated to customize its operation. The sensor system monitors the applied voltage that changes as a sensor transmits data to determine its relative position on the bus and to adjust its parameters accordingly. The sensor system can also compensate for changes in static offset voltage by subtracting an equal voltage in a differential amplifier. The sensor system can be calibrated at the manufacturing facility and can include a lowest voltage to place the sensors in a run mode to allow them to monitor their respective functions and to transmit information to the monitoring system. The relative current drawn by the system and the relative voltage level of these digital pulses will be changed as the resistance of interconnects changes."

Problems solved by technology

Usually, the machinery is relatively complex and more than one sensor is employed to sense more than one parameter, event, or situation.

Other methods also exist to reduce the application cost while not reducing reliability.

This method, however, requires that the sensors not transmit information simultaneously.

Each method is relatively expensive to employ.

Assigning a unique number during manufacture requires complex procedures such as vaporizing metal traces with a laser or burning open diode junctions with high voltages.

Employing a series of switches or other programming means for the end user to uniquely assign numbers increases the size and complexity of the sensor, increasing cost and reducing reliability.

Knowing that a problem is due to simple sensor failure may mean the difference between being able to run the system in a limited mode or having to shut it down, or in operating dangerously when an alarm condition exists that is not being signaled by a broken sensor.

The large static current causes remote monitoring swamping resistors to drop a large portion of the applied voltage that is used to power the sensor.

A problem with the multiplexing of these switched output sensors is that some method must be employed to allow the monitoring system to determine which sensor is in the alarm state if this information is needed.

This greatly complicates the sensor, and requires that each sensor be given a unique number during manufacture or during initial installation.

This usually precludes real-time monitoring of these sensors in a multiplexed arrangement.

It has been found that semiconductor devices such as the three prior art sensors above are usually very susceptible to output changes due to changes in temperature.

Also, extreme temperatures can destroy or damage them.

Prior art sensor monitoring systems do not usually contain temperature compensation for extreme changes in sensor output as a result of temperature changes nor do they supply any indication that the temperature is above a dangerous level.

Two-wire technology is less expensive and more reliable than technologies using more wires.

Two-wire connection of the three main type of prior art sensors, however, is made difficult by various problems specific to the type of sensor being employed.

The analog output position sensor's large DC offset through the monitoring resistor wastes power and reduces effective power supply voltage to all sensors.

First, in the case of mutually exclusive event monitoring, mechanical or electrical limitations on the system preclude any of the monitored events from occurring at the same time.

Second, the situation may be such that we only want to know that all the sensors are in a particular desired situation.

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