Temperature compensated alarm system

• US 4,546,344 A
• Filed: 03/05/1984
• Issued: 10/08/1985
• Est. Priority Date: 03/05/1984
• Status: Expired due to Fees

• Current Assignee: ADT Diversified Services Inc (Johnson Controls International plc)
• Original Assignee: American District Telegraph Company (Johnson Controls International plc)
• Inventors: Guscott, John K., Casamassima, Mario
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US06/586,104
• Time in Patent Office: 582 Days
• Field of Search: 340/501, 340/510, 340/511, 340/517, 340/518, 340/521, 340/522, 340/555, 340/565, 340/588, 340/589, 374/132, 374/133, 374/172
• US Class Current: 340/501
• CPC Class Codes: G08B 21/182 Level alarms, e.g. alarms responsive to variables exceeding a threshold

Abstract

A temperature compensated alarm system includes a temperature transducer operative to produce an electrical output signal indicative of the ambient temperature, an alarm sensor, an electronic processing module, and a plurality of addressable registers for storing alarm threshold limits applicable at the operative ambient temperature. At selected times the electronic processing module reads a value indicative of the ambient temperature and thereupon determines the applicable alarm threshold limits by addressing the respective registers containing threshold limit data for the particular ambient temperature. In one embodiment, two sets of registers are provided; one set of registers containing higher sensitivity threshold limit data and the second set containing lower sensitivity threshold limit data. The applicable threshold data is determined by the state of a user settable switch.

Claims

1. A temperature compensated alarm system comprising:

an alarm sensor having a known temperature characteristic and operative to produce an electrical output signal representative of a desired parameter to be monitored;

a temperature transducer operative to provide an electrical output signal representative of the ambient temperature in vicinity of the transducer;

a plurality of selectively addressable storage registers containing data representative of alarm threshold limits applicable at specified ambient temperatures;

an electronic processing module including;

means for sampling said alarm sensor and temperature transducer output signals;

means for addressing and accessing threshold data from at least one selected register of said plurality in response to said transducer output signal; and

means for generating an alarm signal if said sensor output signal exceeds said threshold data from said at least one selected register.

2. The alarm system of claim 1 including:

a converter operative to produce a digital output signal representative of said alarm sensor electrical output signal;

a converter operative to produce a digital output signal representative of said temperature transducer electrical output signal.

3. The alarm system of claim 2 wherein said alarm sensor is operative to produce an analog output signal having an amplitude which varies responsive to a specified parameter to be monitored, said temperature transducer is operative to produce an analog output signal representative of the ambient temperature, said converter for producing a digital signal representative of said alarm sensor electrical output signal includes an analog to digital converter operative to produce a digital signal representative of said alarm sensor analog output signal;

and said converter for producing a digital signal representative of said temperature transducer output signal includes an analog to digital converter operative to produce a digital signal representative of said temperature transducer analog output signal.

4. The alarm system of claim 3 wherein said means for sampling said alarm sensor and temperature transducer output signals includes means for sampling said digital signal representative of said alarm sensor output signal and said digital signal representative of said temperature transducer output signal respectively.

5. The alarm system of claim 1 wherein selected ones of said plurality of registers contains data representative of upper threshold limits and other selected ones of said plurality of registers contain data representative of lower threshold limits.

6. The alarm system of claim 1 wherein said electronic processing module includes a microcomputer.

7. The alarm system of claim 6 wherein said plurality of storage registers comprises selected registers internal to said microcomputer.

8. The alarm system of claim 7 wherein said selected registers internal to said microcomputer comprise selected read only memory registers.

9. A method for providing temperature compensation in an alarm system comprising the steps of:

producing a first electrical signal having a characteristic representative of ambient temperature;

producing a second electrical signal representative of a specified parameter to be monitored;

selectively addressing at least one digital storage register containing data representative of alarm threshold limits based upon said first electrical signal characteristic representative of ambient temperature;

accessing said threshold limit data contained in said at least one digital storage register; and

generating an alarm signal if said second electrical signal has a value exceeding said threshold limit data.

10. The method recited in accordance with claim 9 wherein said first electrical signal producing step includes the steps of:

providing a temperature transducer operative to produce an output signal representative of ambient temperature;

applying the temperature transducer output signal to a converter operative to produce a digital signal representative of said transducer output signal; and

said addressing step includes the step of selectively addressing at least one digital storage register containing threshold limit data based upon the value of said digital signal representative of said temperature transducer output signal.

11. The method recited in accordance with claim 9 wherein said second electrical signal producing step includes the steps of:

providing an alarm sensor operative to produce an electrical output signal representative of a condition to be monitored;

applying the alarm sensor output signal to a converter operative to produce a digital signal representative of said alarm sensor output signal; and

said generating step includes the step of generating an alarm signal if the digital signal representative of said alarm sensor output signal has a value exceeding said threshold limit data.