MXPA96001056A - Circuit and puls temperature surveillance method - Google Patents

Abstract

The present invention relates to a temperature monitoring circuit comprising a thermistor which is connected to a power supply rail by means of a transistor. The transistor is pulsed to intermittently connect the thermistor in circuit with the power supply. The main power pulled by the thermistor of the power supply is reduced, causing less draining of the power supply

Description

CIRCUIT AND PULSED TEMPERATURE SURVEILLANCE METHOD Inventor: Damián Paul Allinson, of English nationality, residing at 887 Scott Hall Road, Leeds, LS17 6HU, England Owner: S ITCHED RELUCTANCE DRIVES LIMITED, English national, residing at Springfield House, Hyde Terrace, Leeds, LS2 9LN, England.

Background of the Invention This invention relates to a pulsed temperature monitoring circuit and to a method for operating a temperature monitoring circuit. This invention is particularly applicable to an electric motor drive system which comprises a pulsed temperature monitoring circuit.

An application in which a temperature sensitive device can be used is like a temperature sensor in an electric motor drive system. The device is arranged to monitor the working temperature of the motor itself so that the motor controller is able to take this into consideration. Under normal operating conditions the demand on the motor can be limited if the motor temperature rises beyond an acceptable limit.

Various types of temperature transducers are known and which varies a production characteristic of the transducer with a change in temperature. For example, some transducers are known in which a change in the resistivity of a component occurs when the temperature changes. One such type of device is the resistor which is a resistor typically comprising a semiconductor material. The thermistor has a relatively large and generally non-linear temperature resistance coefficient. A generalized illustration of the resistance / temperature characteristic of a thermistor is shown in Figure 1 of the drawings.

Thermistors are often operated on a relatively linear part of the temperature / resistance curve as denoted by the letters a and b in Figure 1. A thermistor will be chosen for a particular application so that the temperature range matches this part relatively more linear d the resistance / temperature curve. Typically, a thermistor in a temperature monitoring circuit will have a regulated fixed supply voltage and will be configured in a potential divider network through the supply voltage.

However, it will be clear from Figure 1 that the overall resistance / temperature characteristic is more of a tub shaped curve even though this is rarely considered by the thermistor user because a characteristic outside the generally accepted working range does not It is of interest to the user.

The known thermistors operating through a wide temperature range (for example between -20 ° C and + 80 ° C) will oscillate in resistance between, say 20 ohms and 2kohms. D according to Figure 1 there is a very large variation in the pulled current of the constant voltage supply through known potential divider circuit. At low temperatures there is a drainage of particularly heavy current. In addition, a temperature sensing circuit including a thermistor operating over a wide temperature range would have to be designed for the heavier current situation, for example, low temperatures.

In an extreme environment, such as a cold store or cold store, a charging vehicle driven by an electric motorcycle may require having its motor temperature monitored over a wide range of temperature. In situations in which the motor is operated while it is in the refrigerated store or the motor is not heavily loaded, the resistance of the thermistor can be low and the drain of the regulated supply is increased accordingly.

As part of the motor control system on a battery operated vehicle typically there is a voltage regulator which derives a lower control circuit voltage from the main battery voltage. If the battery is at or near a full charge and the drainage of current attributable to the thermistor is high, the regulator will be particularly heavily charged and will have to be designed with a capacity such that it will not overheat in the worst case.

To avoid overheating the regulator, it is also known to provide a heat sink to dissipate the heat generated by the regulator. Using either a larger capacity regulator or a heat sink requires a space in an engine compartment in which space may not be available in abundance.

It is an object of the present invention to provide a temperature monitor for use over a wide temperature range which, on average, pulls considerably less current than those known in the prior art.

According to the present invention there is provided a temperature monitoring circuit comprising a temperature sensing device, having an electrical characteristic that varies with the temperature, or power supply, an output terminal that provides an electrical output dependent on the temperature of the temperature sensing device, a switch set for capacitating the monitoring circuit, the interruption arrangement being connected between the power supply and the temperature sensitive device, and a controller for driving the switch means according to capacitive pulsations repeated.

In one embodiment of the invention the temperature sensitive device is a thermistor which has a normal temperature operating range based on a relatively linear part of its temperature / resistance curve. According to the invention, the full temperature range of the temperature / resistance curve can be used, including it is part in which the resistance is at the lowest. The pulsing of the monitoring circuit intermittently capacit the thermistor and the pulling of the main energy of the power supply is therefore reduced accordingly.

Preferably, the switch arrangement includes a transistor, for example a bipolar NPN transistor.

Also according to the invention there is provided a method for monitoring the temperature of a body using a temperature-sensitive device having an electrical characteristic that varies with temperature, the method comprising: (a) connecting the temperature sensing device to a power supply; (b) capacitate the sensitive device of the temperature by means of a switch assembly according to repetitive capacitive pulsation.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be practiced in various ways some of which will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an idea resistance / temperature curve for a thermistor; Figure 2 is a schematic block diagram of a switched reluctance driving system in which the invention is used; Figure 3 is a schematic block diagram of a temperature monitoring circuit according to the invention and Figures 4 a) and 4 b) are circuit diagrams of an alternate form of the invention using an oscillator and comparator.

Detailed description of the invention Referring to Figure 2 of the drawings, a switched reluctance motor drive system comprises a switched reluctance motor 10 which is controlled by a controlled 12, comprising a microprocessor 14 and a function card number 16, one of the which is shown. In this modality the microprocessor 14 is a 68HC11 processor which is manufactured by Motorola, Inc. The motor 10 has a shaft 18 which is connected to a load 20. The load 20 may be any which is to be rotated by the motor 10. how to be obvious to an expert person. In a particular application, the load 20 is constituted by the traction wheels of a loading vehicle used in a cold store. Other perhaps static applications in an extreme environment or in a temperature range (such as motors for conveyor belts in a cold store) are also applicable to the invention.

The motor 10 and the drive system are generally known in the art and will not be described in greater detail here. An example of switched reluctance motors and drive systems is the document "The Characteristics, Design, Applications of Switched Reluctance Engines and Stephenson & - Blake drives, PCIM Conference, June 21, 1993 Nurnberg, Germany.

The motor 10 and the controller 12 are supplied from a battery 22 in this mode. Of course, other sources of electric power may be used, such as the main rectified supply. The output of the battery 22 is regulated at 5V for the control circuit by a DC voltage regulator 24. A thermistor 26 is mounted on the cover 28 of the motor 1 to monitor the temperature of the motor or in the winding of the motorcycle to monitor the temperature of the winding. The thermistor output 26 is assigned to the function card 16.

Figure 3 shows the thermistor 26 in circuit. This is in effect a detail of the card 16 in figure 2 except of course, because the thermistor is mounted on the engine cover 28 and the battery 22 is also mounted separately from the card 16. The regulator 24 provides a stable 5-volt output regardless of the battery's charge status.

A resistor 30 is connected to the regulated 5 volt supply rail. An NPN bipolar transistor 32 is connected in series between the resistor 30 and the thermistor 26 which is, in turn, connected to the potential to ground. It will be apparent from FIG. 3 that the collector of the transistor 32 is connected to the resistor 30 and the transistor emitter 32 is connected to a thermistor 26. A resistor 34 is connected to the transistor base 32.

It will be appreciated by a person skilled in the art that other types of semiconductor switch, such as a field effect transistor or an electromechanical switch, such as a relay can be used in place of transistor 32 in certain applications with an equal effect. It will also be appreciated that the thermistor may be mounted on a piece of equipment distinct from the motor, for example, a thermal sink for power switch devices.

The transistor 32 is provided with a capacitive pulsation at its base from the programmed microprocessor 14 which changed the thermistor 26 inside and outside the circuit providing for both capacitive signals. The output 36 of the thermistor circuit is a voltage level taken between the collector of transistor 3 and the potential to ground. As the temperature of thermistor 26 rises, its resistance follows the tub curve of Figure 1. Over most of the range of operation of the thermistor this is equal to more or less a stable rise in resistance with temperature. The thermistor 36 is chosen so that the more linear operating characteristic matches the temperature range critical to the acceptable operation of the motor. This would be the practice accepted by an expert person. The present invention is directed to a situation in which the environment in which the motor is operating extends far out (in this case below) of the critical range and even the thermistor is required to monitor the temperature of the motor. In a refrigerated cold store, for example, there will be occasions when the 10-second engine becomes inoperative in conditions below the freezing point so that the thermistor output reflects the climatic temperature until the engine warms up. When the lower perceived temperature is released, the resistance of the thermistor will be towards the lower part of the operating curve, for example around 20 ohms. This leads to a considerable draining of current from the regulated supply and comparison with drainage and current when the resistance of the thermistor is between 500 and 2000 O.

Until now, the regulator had dealt with the highest level of direct current drainage. As a result of this, the voltage regulator has to be of sufficient capacity to cope with the draining of current through the thermistor at the lowest point on its temperature / resistance curve.

The situation is further exacerbated by the possibility that the battery may have been recently charged and, therefore, be particularly healthy, if only for a short but appreciable time, at the same time that the drained d current through the thermistor is in the heaviest. A 24-volt battery can have a current voltage output range of about 15 to 32 volts. It will be evident that a higher battery voltage will cause an increased load on the 5 volt regulator. The pull of thermistor current and the higher battery voltage require that the regulator be designed to deal with this. A larger capacity regulator takes sufficiently more space in an engine compartment in the situation where space is not in abundance.

According to the invention, the pulling of current on the regulator is limited by the pulsation of the transistor in order to capacitate the temperature monitoring by interrupting the thermistor outside and inside the circuit. Therefore, the energy drawn by the thermistor over a period of time is limited by the duty cycle of the pulse waveform used. An additional benefit is that of allowing the monitoring circuit components (particularly the resistor 30) to also have smaller energy management capabilities.

In this particular mode, the microprocessor is programmed to provide the monitoring circuit with a variable duty cycle. When the perceived temperature of the motorcycle rises to the critical operating range, the duty cycle increases. In the critical range where temperature monitoring is most important the duty cycle could be 100% d, for example completely "on". In the critical range continuous monitoring can be carried out even when it may not be used.

Within a predetermined temperature range of particular importance, the duty cycle of the capacitor pulsations may be increased, even though this will increase the energy consumption. Alternatively, if a particularly long duration is used between the pulsations outside of an important temperature range, the frequency of the pulsations may be increased in that range or when approaching it. Although the advantage of the invention lies in pressing the thermistor to save energy, it is also possible to capacitate it continuously in a temperature range where the temperature and critical monitoring is carried out.

In an alternate mode, a fixed pulsation of the monitoring circuit transistor may be employed. For example, a free run oscillator output can be used to provide regular pulses to capacitate the monitoring circuit.

Figure 4 a) shows a pulse generator 40 which provides a capacitive pulse output 44 connected to the input to the base of transistor 32 in FIG. 3. In FIG. 4 b) the capacitive pulse connects to the thermistor 26 as shown in FIG. output of the regulator 24 by making the transistor s conduct as before. An output 46 of the thermistor potential divider network is connected to an input au comparator 48 that provides an output when the thermistor capacitor circuit output exceeds a preset input to comparator 48. The preset input is set by a voltage divider. further comprising the resistors 50 and 52 connected to the regulator 24. Thus, a pulse output from the comparator 48 was used as the signal pair by the microprocessor 14 to perform interruption functions on temperature. Again, the thermistor is only capacitated for the period of capacitive pulsation, conserving for all energy. The frequency of the capacitive pulsations can be changed by altering the values of the resistor r and / or capacitor C in the pulsation generator of Figure 4 (a) Similarly, the duration of each pulsation can be changed by changing the value of the resistor R .

It will be apparent to one skilled in the art that thermistors with positive temperature coefficients or negative temperature coefficients can be employed in various embodiments of this invention. Although such various modalities may involve minor revisions to the circuit shown in Fig. 3, the basic method is not changed.

The invention is particularly described in relation to a switched reluctance motor. It will be readily appreciated by a person of ordinary skill in the art that electric motors, generators or other pieces of electrical mechanical equipment may employ the same thermistor temperature monitoring circuit to an equal effect.

Even when the described controller is based on a microprocessor it will be evident to an expert that other forms of controller can be used. For example, a hard wiring control board can be used by executing a fixed routine or a comparator-based controller.

Although the invention has been described in connection with the illustrative embodiments discussed above, those skilled in the art will recognize that many variations may be made if depart from the present invention. Therefore, the above mentioned description of several modalities is done by way of example and not for purposes of limitation. The present invention is intended to be limited only by the spirit scope of the following clauses.

Claims (16)

CLAIMS Having described the invention, it is considered as a novelty, and therefore the content of the following clauses is claimed as property:

1. A temperature monitoring circuit comprising a temperature sensitive device having an electrical characteristic that varies with temperature, or power supply, an output terminal which provides an electrical output that depends on the temperature of the device temperature. Sensitive, a switch set to capacitate the monitoring circuit, the switch arrangement being connected between the power supply and the temperature-sensitive device, and a controller to drive the switch arrangement according to the repeated capacitor pulses.

2. A circuit as claimed in clause 1, characterized in that the control means is arranged to vary the duty cycle of the pulsations to vary the production of the device.

3. A circuit as claimed in clause 1, characterized in that the control means is arranged to vary the frequency of the pulsations as the production of the device varies.

4. A circuit as claimed in clause 1, characterized in that the control means is arranged to drive the switch arrangement according to a first pulse frequency for a temperature afuer of a predetermined range and a second frequency d pulsations for a temperature within a predetermined temperature range.

5. A circuit as claimed in clause 1, characterized in that the control means is arranged to drive the switch arrangement according to a pulse cycle for a temperature outside a predetermined temperature range and continuously to capacitate the circuit for temperatures within the predetermined temperature range.

6. A circuit as claimed in any of clauses 1 to 5, characterized in that the temperature sensitive device is a thermistor.

7. A circuit as claimed in any of the preceding clauses, characterized in that it includes a network in which the sensib device is connected to the temperature.

8. A circuit as claimed in any of clauses 1 to 7, characterized in that production of said device is fed back to the controlled controller being arranged to increase the pulse frequency or the working cycle of the pulses by varying the output of the device sensitive to temperature in response to the temperature of said device.

9. A circuit as claimed in any of clauses 1 to 8, characterized in that the switch arrangement includes a transistor.

10. A circuit as claimed in any of clauses 1 to 9, characterized in that the controller includes a microprocessor.

11. A circuit as claimed in any of clauses 1 to 10, characterized in that it is part of a driving system for an electric motor.

12. A circuit as claimed in any of clauses 1 to 11, characterized in that the power supply includes a voltage regulator. w »19 13.

A method for monitoring the temperature of a body using a temperature sensitive device having an electrical characteristic that varies with temperature, the method comprising: (a) connecting the temperature sensitive device to a supply of energy by means of a switch arrangement; Y 10 (b) capacitate the temperature sensitive device by means of the switch arrangement according to repeated capacitive pulsations. 1 .

A method as claimed in Clause 13, characterized in that the working cycle of the pulsations is varied by varying the production of the device.

15. A method as claimed in clause 13, characterized in that the frequency of the 20 pulsations is varied by varying the device's output.

16. A method as claimed in any of clauses 13 to 15, characterized in that the temperature sensitive device is a thermistor. 25 In testimony of which I sign the present Mexico, D.F., on March 20, 1996 LIMIT Attorney SUMMARY A temperature monitoring circuit comprising a thermistor which is connected to a rail d power supply by means of a transistor. The transistor is pulsed to intermittently connect the thermistor to the circuit with the power supply. The main energy pulled by the thermistor of the power supply is reduced, causing less drainage of the power supply.