Alarm circuit

Details Alarm circuit Alarm circuit

1980-09-22

1982-08-24

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

With particular system function

340635, 340679, 361 23, 417 63, G08B 2900

Patent

active

043463711

ABSTRACT:
An alarm switch circuit includes an opto-isolator that is used as a high speed switch to control the pulse generation rate of an oscillator circuit which in turn maintains a set of normally open contacts of an interlock relay in the closed condition. The fail-safe design features are not negated should the following conditions occur: (1) a loss of power, (2) one or more independent failures of circuit elements, (3) open or short circuit failures of the set point (SP) or process variable (PV) voltages or their polarity reversals and (4) the background noise masks the PV signal.

REFERENCES:
patent: 3509359 (1970-04-01), Embling
patent: 3588857 (1971-06-01), Gessner
patent: 3831161 (1974-08-01), Enabnit
patent: 3854089 (1974-12-01), Emler
patent: 4059845 (1977-11-01), Kolkman
"Design of Fail-Safe Control Systems", J. A. Bryant Power (pp. 52-56) Jan. 1976.

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