TWARSES The Two Wire Automatic Remote Sensing and Evaluation System

Abstract

The Two Wire Automatic Remote Sensing and Evaluation System (TWARSES) automatically transmits and evaluates information (data) from remote sensors on a common two wire buss. In addition the system presents automatic evaluation and alarms, which provide both location data and sensor readout data of the monitored area. This system is a stand-alone modular system in which a common two wire line installed bow-to-stern and top-to-bottom, connects, integrates, evaluates, and powers a multiplicity of sensors. The United States Navy uses this system to provide safety and survivability by monitoring environmental gases, liquid levels, and power, temperature, and humidity levels on ships and in office buildings. The automatic monitoring system operates in a manner similar to an automatic, multiscriber, party-line telephone system. The system is controlled by the Scanner/Display unit which interrogates each of the 150 possible sensors according to the program stored in a microprocessor. This patented system provides a separate address for each sensor transponder, permitting all of the transponders to be simply connected in parallel across a common, twisted pair transmission line. The interrogating signal is also used to provide power (6V - 2mA) for the sensor transponders and their associated sensors. This further simplifies the system by eliminating the need for a separate source of power at each sensor location. Each sensor is interrogated with a 15-bit sequence which specifies: (1) the address of the sensor which is to reply, (2) the parameter to be reported (e.g. voltage, temperature, humidity, etc.) And (3) the desired precision (which sets the length of the reply). The interrogation is transmitted as frequency shift-keyed signal. Among the various types of interrogation signals which could be used (AM, FM, etc.) frequency shift-keying (FSK) was selected because: