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Fail Safe Self Checking Level Control System

IP.com Disclosure Number: IPCOM000074204D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Johnson, LA: AUTHOR [+2]

Abstract

In a fail safe control system for checking the level of heated liquid in a container, an alarm occurs when either the sensors or the controls fail.

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Fail Safe Self Checking Level Control System

In a fail safe control system for checking the level of heated liquid in a container, an alarm occurs when either the sensors or the controls fail.

Primary level sensing probes PHI and PLO sense the high and low levels of liquid in the container. Safety probes SHI and SLO are provided to detect high and low levels exceeding those detected by the primary probes. Entry of liquid into the container is controlled by a solenoid and relay CR2, and the application of heat is controlled by a relay CR3. Control logic responds to signals supplied by any commercially available level controller*, as a function of liquid levels in the container and operates the liquid valve, heater, or an alarm CR1.

Signal P closes a relay CR4 when liquid is as high as probe PHI, which is held as long as the liquid is higher than probe PLO. Signal S opens relay CR5 when the liquid level is higher than probe S/LO and CR4 is closed.

AS the level in the container rises from its normal level to reach the probe PHI, the liquid valve is turned off and the heater is turned on. When the liquid falls below probe PLO, the liquid turns on and the heater turns off. If the liquid relay CR2 or the heater CR3 remains on, when it should be off, an alarm will be signaled. Any condition not provided for in normal fill and drain operations also results in an alarm. Substantially all contacts are arranged to be tested during normal fill and drain operations.

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