US2553603A - Rate-of-rise temperature responsive system - Google Patents

Description

y 2, 1951 M. F PETERS 2,553,603

RATE-OFRISE TEMPERATURE RESPONSIVE SYSTEM Filed Aug. 16, 1949 INVENTOR NELV/LLE E P571525 JcZM/w'zm, 9 Wm A I tornays Patented May 22, 1951 RATE-OF-RISE TEMPERATURE RESPON- SIVE SYSTEM Melville F. Peters, East Orange, N. J., assignor to Petcar Research Corporation, Newark, N. J., a corporation of New Jersey Application August 16, 1949, Serial No. 110,649

4 Claims. 1

This invention has to do broadly with devices and systems for providing an indication, effecting a control operation or performing some other function in response to a change in temperature. More particularly, the invention relates to that class or type of such devices which are operated upon a rapid rise in temperature but which remain inoperative if the rise in temperature is gradual. Such devices and systems are particularly useful for fire detection and while my invention has many other applications and uses, it will be described in this application as a fire detection system.

There has heretofore been invented, and is now available, a temperature-responsive device or system comprising or including an element having two continuous, electrically conductive wires spaced apart and surrounded by material (known as Thermistor material) which has a very high electrical resistance at normal temperatures and a lower resistance at a predetermined temperature higher than normal. This element is disclosed and claimed in the co-pending application of Melville F. Peters, Serial No. 90,881, and a complete temperature-responsive system including such an element and useful for the various purposes set forth above is disclosed and claimed in the co-pending application of Melville F. Peters, Serial No. 105,423, now abandoned. Devices and systems incorporating and dependent upon such elements do not operate on rate-ofrise but, rather, on the occurrence of a pre-determined temperature applied to the element.

It has been my object, which is achieved and accomplished by this invention, to provide a temperature-responsive system useful for the various purposes set forth above incorporating and dependent on a thermistor-type element as described above but operating on the rate-of-rise principle and being therefore operable to produce an indication or effect a control or other useful operation on rapid rate of rise in ambient temperature at the location of the thermistor element. A rate-of-rise system incorporating and dependent upon a thermistor element has never before been provided and has many advantages not found in known rate-of-rise systems among which are the cheapness and ease or manufacture of the thermistor element as compared to the temperature-responsive elements of known rateof-rise system, and the additional but very important feature that a system according to this invention may be set to operate at some predetermined temperature regardless of the rate at which the temperature increases to this pre-de- 2 termined point. It will be apparent that this latter feature of my invention insures that warning will be given, or other operation provided, if a pre-determined dangerous temperature is reached.

Other objects, results and new features of my invention will be made apparent by the description in this application of two systems embodying the invention, which are illustrative of the invention but impose no limitation thereon not imposed by the appended claims.

The three figures of the drawings of this application are circuit diagrams of three temperatureresponsive systems according to the invention.

In Fig. 1 there is disclosed a temperature-responsive system which is operative to cause an operation, for example, to energize a signal, on rapid (as opposed to gradual) rate of rise of temperature, but which is not operative to cause such operation on increase in temperature to a predetermined point. Thus, in a fire detector system according to Fig. 1, a signal will be provided on rapid rise of temperature, such as occurs on combustion, but this signal will be discontinued when the temperature stabilizes, as will be the case after combustion is well under way. The system of Fig. 1 comprises a source of electric energy 2, being a transformer having a resistance 4 connected across its secondary. A fixed resistance 6 and a variable resistance 8 are connected in series as a bridge across the resistance 4 through an adjustable tap at point a by means of which the voltage across the series-connected resistors may be varied. The resistor 8 is a temperature-responsive element comprising two wire conductors l0, I2 spaced apart and surrounded by thermistor material, all as described hereinbefore. The connecting point 17 between resistors 6, 8, i. e. the mid-point of the bridge, is connected through lead [4, resistor H5 connecting point z and lead 3, to the grid of the three-element vacuum tube 20 is also connected through lead I4, resistor 22, connecting point 5 condenser 2 and lead I8 to the same grid and, further is connected through leads M and 2G to the cathode of tube 20. The anode of the tube is connected to one terminal of a signal device 28, the other terminal of which is connected to a part of the secondary of transformer 2 which is out of phase with the part supplying energy to the resistance bridge 6, 8. The connecting point 0 between resistors 4 and 8 is connected through a rectifying device 30 (which in the drawing is shown as a diode rectifier) and condenser 24 to the grid of tube 20.

The described connection of circuit elements causes resistor 22 and rectifier 30 to be connected in series with the resistance of the variable resistance 8, and resistance 22 is therefore supplied with pulsating direct current. One of the terminals of condenser 24 is connected to one terminal of resistance 22 and the other is connected equilibrium whereby voltage stored in condenser 24 is not released to resistor [6.

In the operation of the described system, it being assumed that temperature-responsive element 8 is normally subject to stable temperature conditions, with a constant voltage applied across voltage divider a-c and with a constant voltage ratio (4-?) to 22-0 to ac, the voltage on condenser 24 will reach a steady value equal to the voltage drop across resistor 22, and points I) and i will therefore be equi-potential. As the cathode and grid of tube 25 are respectively connected to points I) and i no current will flow in the tube and the signal circuit will be tie-energized.

If, now, a rapid rise in temperature occurs there will be a consequent reduction in the resistance of detector element 6, a resulting rapid change in voltage be and a rapid decrease of potential difference between points I) and As the voltage across points I) and 51' rapidly decreases a condition occurs in which the voltage across condenser 24 becomes momentarily larger than it would be under a condition of circuit equilibrium and therefore the condenser discharges through resistor i8 which has the function of controlling the rate of discharge of the condenser. During this discharge, a voltage is developed across resistor it, i. e., between points I) and i which were equipotential during circuit equilibrium, which results in a more positive voltage being applied to the grid of tube 29, causing current to flow in the tube and in the signal circuit, thus operating the signal. This circuit provides a signal only v hile a rapid rise in temperature is in progress and for a limited time thereafter. It does not operate to energize the signal when a predetermined temperature is reached after a slow rise nor will any ultimate steady temperature continue the signal. A slow rise in temperature will not operate this system as the values assigned to the resistor 15 and condenser 24 are such that a slow change in-the charge on condenser 24 will tak place with an accompanying very small change inpotential between points b, 1' across the condenser-bleeding resistor Hi. The potential across points I), i is so small in this case that it will be ineffective in energizing the tube 20. The sensitivity of tube 22 is controlled by the adjustment of the point a on voltage divider a c and for the above case it is set to be insensitive to the very small potential across points 79, 2' when a slow rate of temperature rise occurs.

In Fig. 2 of the drawings there is disclosed a modified system according to the invention which not only operates on rapid rise in temperature but also on rise (regardless of rate) of ambient temperature to a predetermined value. The sole difference between this circuit and that of Fig. 1 lies in the connection of the cathode of tube 20 to point 0 by lead 38 inthe circuit of Fig. 2 rather than to point b as in Fig. 1. The ultimate am-' bient temperature which will operate the system after a slow rise, or continue its operation after a rapid rise, is determined by the setting of the adjustable tap at point'a and the consequent voltage ratio ac to be. The rates of rise to which the tube 20 will respond are determined by the values of resistance and capacitance assigned to resistors I8 and 22 and condenser 24 and in the case of a rapid rise the circuit will function as described in the case of Fig. 1. In the case of a slow rate of rise the tube will not respond to the very small voltage developed across points b, i and the system will not operate to provide an indication, all as described hereinbefore in connection with Fig. 1.

This system will respond to an ultimate ambient temperature regardless of the rate of rise to such temperature, for the reason that if there is a slow rateof rise the potential between points b and i is very small and is ineffective to control the tube, as previously described in connection with Fig. l, and. therefore the control grid of tube 20 is in effect connected to point b and consideration of potential difference between points b and 2' may reasonably be neglected. In such a case the circuit resembles and operates in the same manner as those described in my co-pending application Serial No. 105,423, to which reference is made for a more complete understanding of such manner of operation. Further, the tube 26 responds to a change in voltage across points 5, c by reason of a change in the resistance of the temperature-sensitive element 8 and therefore will respond atsome predetermined temperature as provided in the above-mentioned application.

A preferred detector system embodying the invention is disclosed in Fig. 3 and comprises the detector system of Fig. 3 of my co-pending application Serial No. 105,423 modified to provide an indication on rapid rise of temperature and on increase of ambient temperature to some pre-, determined degree, regardless of rate of rise. The system and its operation are fully described inthe aforesaid co-pending application andref: erence is made thereto for a complete understanding of the arrangement and operation of the basic circuit. For the purpose of better'understanding of the invention, the reference numerals of Fig. 3 of my co-pending application have been applied to Fig. 3 of this application.

According to the present invention this basic circuit is modified by the introduction of the rateof-rise circuit between the point b, which is the connection between the fixed resistor 52 and the variable resistance detector element A, and the grid of tubeiifi. This rate-of-rise circuitoperates to control flow of current in the circuit of tube 56 to cause operation thereof on rapid rate of rise of temperature. The operation of the rate-of-rise circuit is described hereinbefore in connection with Fig. 1 and will not be repeated here. It will be noted that a resistor 59 is connected in series with the grid of tube 56 for the purpose of limiting grid current and preventing tube damage. This resistor forms no part of the invention but is normally used in the embodi ment disclosed in Fig. 3. The circuit of Fig. 3 will operate to energize the signal 42 on increase in ambient temperature to any predetermined degree in accordance with the normal operation thereof as described in the aforesaid co-pending application.

While I have described and illustrated certain embodiments of my invention, it will be evident to those skilled in the art that other embodiments, as well as modifications thereof, may be made without departing in any way from the spirit or scope of the invention, for the limits of which reference must be made to the appended claims.

What is claimed is:

l. A temperature responsive system comprising a circuit including an operating device, a source of voltage, a grid-control tube for controlling the 1 energization of the circuit, and means for controlling said tube to cause the circuit of the 0 erating device to be energized on rapid rise of temperature, said means comprising a source of voltage and a fixed resistance and a variable resistance connected in series as a bridge across said source, means connecting the midpoint of said bridge to the grid of said tube, said variable resistance having substantially infinite resistance at normal temperatures and a finite resistance at a higher temperature which finite resistance is so related to the fixed resistance that at normal temperatures voltage developed at the midpoint of the bridge is inoperative to cause operation of the tube, means included in the connection between the midpoint of said bridge and said grid to provide a source of voltage for controlling said grid, means for normally storing rectified voltage and connected to supply such voltage to the grid-control means, means connected to the midpoint of the bridge and normally operative by voltage developed at the midpoint of the bridge at normal temperatures to prevent the supply of voltage from the storage means to the grid-control means and operative upon rapid reduction of the resistance of the variable resistor upon rapid increase in temperature to cause voltage stored in the storage means to flow to the gridcontrol means to operate the grid to energize such circuit.

2. A system according to claim 1 in which the grid-control means comprises a resistance connected in series between the midpoint of the bridge and the grid.

3. A system according to claim 1 in which the means for storing voltage and maintaining voltage in said storing means comprises a condenser having its one terminal connected to the connection between the grid-control means and the grid and its other terminal connected through a resistance to the midpoint of the bridge.

4. A system according to claim 1 in which the means for controlling the grid, storing voltage and releasing it to the grid control means, and maintaining voltage in the storage means comprises a resistance connected in series between the midpoint of the bridge and the grid and providing a source of voltage for controlling the grid, rectifying means and a fixed resistance connected in series with the variable resistance whereby a pulsating direct current appears in said fixed resistance, and a condenser having its one terminal connected to one terminal of said fixed resistance and its other terminal connected tl rough said grid-controlling resistance to the other terminal of said fixed resistance.

MELVILLE F. PETERS.

No references cited.

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