Centralized monitoring system for gas leakage

A centralized monitoring system for gas leakage comprising:

• a plurality of gas leakage detectors disposed in an area to be monitored for continuously measuring the concentration of the gas at each sensing point in the area and for generating an analog signal representative thereof, said plurality of gas leakage detectors being grouped into a plurality of groups;
• a plurality of remote terminal units each connected to a corresponding one of said plurality of groups of gas leakage detectors, each of said plurality of remote terminal units including,
• a scanning analog-to-digital converter for continuously scanning the analog signals from said group of gas leakage detectors and for converting the analog signals into digitally coded block data,
• a data register circuit connected to said scanning analog-to-digital converter for storing said block data which is continuously updated by said scanning analog-to-digital converter,
• a receiving circuit for receiving an address code, and
• a transmission circuit for checking the coincidence of the received address code with an assigned address code retained in an address register and for transmitting back the contents of said data register circuit together with the address code when the coincidence of the address is obtained;
• a loop line for interconnecting said plurality of remote terminal units in a loop, said loop line having two cables one being connected to said receiving circuit and the other being connected to said transmission circuit in each of said plurality of remote terminal units;
• and
• a central monitoring station connected to said loop line, said central monitoring station including,
• an address code generating circuit having a pulse generator and a counter for generating an address code for each of said plurality of remote terminal units,
• a reception error checking circuit for checking the coincidence between the address code transmitted back from the remote terminal unit and the address code generated and retained in said address code generating circuit and for checking the coincidence between two successively received block data, said reception error checking circuit generating a coincidence signal separately for each of the coincidence of the address code and the coincidence of the block data,
• a gate circuit connected to said reception error checking circuit for permitting the address code and the block data to pass therethrough only when the two coincidence signals are received from said reception error checking circuit,
• a monitor unit connected to said gate circuit for comparing the block data transferred through said gate circuit with a predetermined monitor level for each sensing point as well as each group of sensing points and for displaying and recording the status of the gas-concentration conditions, and
• a switching circuit for switching between two terminals of each of the transmission and reception cables of said loop line, said switching circuit being connected to said gate circuit and said address code generating circuit and wherein when the coincidence of both the address and the block data is not obtained or when no address and block code are transmitted back to said central monitoring station said switching circuit is actuated by a control signal from said gate circuit to thereby switch between the terminals of the transmission and reception cables.