Browse Prior Art Database

Supervision Device for Contact Sense Points

IP.com Disclosure Number: IPCOM000044688D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR [+2]

Abstract

This article describes a supervision device which provides detection of line faults, such as short circuits, on sense or alarm lines that utilize normally closed circuits. The device disclosed herein allows the user to supervise contact sense lines when these lines support sensor devices utilizing normally closed (N.C.) sense switches or similar switch schemes. While this was possible in the past, it often required resistor networks at the sensor and its use was frequently negated by high loop resistance in the lines connecting the sensor to the central station, computer center, or like facility. In the present scheme the loop resistance is not critical, and with the values shown in Fig. 1, loops between 0 ohms and 300 ohms are easily tolerated. Referring to Fig.

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Supervision Device for Contact Sense Points

This article describes a supervision device which provides detection of line faults, such as short circuits, on sense or alarm lines that utilize normally closed circuits. The device disclosed herein allows the user to supervise contact sense lines when these lines support sensor devices utilizing normally closed (N.C.) sense switches or similar switch schemes. While this was possible in the past, it often required resistor networks at the sensor and its use was frequently negated by high loop resistance in the lines connecting the sensor to the central station, computer center, or like facility. In the present scheme the loop resistance is not critical, and with the values shown in Fig. 1, loops between 0 ohms and 300 ohms are easily tolerated. Referring to Fig. 1, in normal operation, when clock phase 1 is high, transistors Q1 and Q2 will be in conduction. This condition will allow current flow through the telephone line, the N.C. contact at the sensor, the silicon diode, the optical (opto) coupler, and the 600-ohm limiter resistor. Typical operation will center on 400 Hz. At this time, the output transistor of the opto- coupler will be conducting and the output will be low. This output will be compared with clock phase 2 which will be low at this time, indicating normal operation. The comparison of these two signals will be accomplished via computer digital input circuits in our application but can readily be accomplished via logic gates by someone skilled in the art. In due time clock phase 1 will go low, and clock phase 2 will go high. Clock phases will also be computer- controlled via digital output circuits, but again could be accomplished with hardware, as shown in Fig. 2. Clock phase 2 being high will allow transistors Q3 and Q4 to be forward biased, while clock phase 1 being low will reverse bias Q1 and Q2. Under normal conditions no current will flow through the loop as the silicon diode located in the sensor enclosure will be reverse biased. The opto- coupler will be in an off state and the output transistor Q5 will not be conducting, with the resultant output being high. This high will be compared with clock phase 2, and both signals being high will indicate normal operation. Activation of the sensor, resulting in the N.C. contacts opening, will result in an absence of loop current during clock phase 1. This condition will result in a high output from the opto-coupler output transistor Q5 which will not compare equally with the clock phase 2 signal. This unequal condition will signal activation of the sensor device. In practice, we will refer to this condition as an "alarm" condition. Additionally, this condition will be encountered if a line is severed. In the event that the lines are shorted to one another, whether by accident or tampering, or if both lines become shorted to house ground, a second condition or state will occur. We will refer t...