Browse Prior Art Database

Combined Air Flow and Temperature Detector

IP.com Disclosure Number: IPCOM000086360D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Alford, JA: AUTHOR [+3]

Abstract

A detector is described which uses a double-thermistor bridge circuit responsive to the presence of a minimum air flow or a temperature level of the air flow. An air flow is divided between two ducts in parallel, each duct containing a thermistor, one of which also contains a heater resistor.

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Combined Air Flow and Temperature Detector

A detector is described which uses a double-thermistor bridge circuit responsive to the presence of a minimum air flow or a temperature level of the air flow. An air flow is divided between two ducts in parallel, each duct containing a thermistor, one of which also contains a heater resistor.

Fig. 1 shows the arrangement of duct 1 containing thermistor TH1 located adjacent to 1/4 watt heater resistor Rl separated by a partition from duct 2 containing thermistor TH2. The ducts are in an air flow which may be upwards or downwards.

Fig. 2 shows the circuit diagram of the double bridge. An air flow bridge is formed by resistors R2, R3 and thermistors TH1, TH2 with balance detected by air flow comparator C1. In the presence of the air flow thermistors TH1 and TH2 are at the same temperature. When the air flow ceases, thermistor TH1 is heated by resistor R1 to unbalance the bridge and operate the reed relay. The circuit detects reduction of air flow below 30 ft/min over the range 0 degrees C to 70 degrees C from sea level to 7,000 feet.

A temperature bridge is formed by resistors R3, R4, R5 and thermistor TH2 with balance detected by temperature comparator C2. In this bridge R3 = R4 and the value of resistor R5 is selected so that the bridge output voltage reverses at the desired temperature.

Comparators C1 and C2 are arranged to provide a current through coil K under normal conditions to hold the reed relay on. Under fault co...