FR2761756A1 - SAFETY DEVICE FOR A STOVE COMPRISING A SENSOR MEASURING THE THERMAL CONDUCTIVITY OF GASES - Google Patents

Abstract

The invention relates to a safety device for a heating device with solid, liquid or gaseous fuel, the combustion of which it is desired to stop as soon as a predetermined rate of dangerous or unwanted gas is reached in the environment of the device, characterized in what it comprises a detection assembly (C) mainly composed of a sensor (A) measuring the thermal conductivity of the gases.

Description

The present invention relates to a safety or regulation device

  for heating apparatus with liquid, solid, gaseous fuel, in particular but

  not limited to mobile petroleum heater.

  In mobile petroleum devices, heat is produced by catalysis of the fuel brought into the catalysis zone by capillarity by means of

of a wick.

  An actuator or operating mechanism makes it possible to control the output

  or erasing the wick in a wick holder and thereby extinguishing the stove.

  This type of device must be equipped with a safety system requiring its total shutdown by extinction before the CO2 content of the room reaches predetermined thresholds and prohibiting the possibility of re-ignition as long as the cause having

  reasoned for this judgment has not disappeared.

  Currently, the standard requires total shutdown for a CO2 level of between 0.6 and 1%. This CO2 level is currently very difficult to measure in

this range of values.

  There is only one known infrared detector capable of fulfilling this function reliably, but its price is very high and its use on an oil stove resulted in doubling the cost price of the device. A consumer application from

  this type of detector is therefore not possible.

  To solve this problem, the current solution is to indirectly assess the CO2 level by measuring the temperature in the vicinity of the device only in a sealed laboratory room and under certain environmental conditions. Under these boundary conditions, this temperature is correlated with the rate of CO2. Such devices are for example described in documents US-A-4,493,634, EP-A-0

  075 602 and FR 95 03236 of the applicant.

  This solution uses multiple components (probe, thermostat, thermocouples or others), and its reliability and accuracy depend in particular on the type of living room, the temperature taken, the number of components, etc. Applicant proposes a new solution to this problem which makes it possible to directly measure a level of CO2, for example less than 1%, without

  significantly increase the price of the device.

  The Applicant had the idea of using a gas detector operating on

  the principle of the thermal conductivity of gases.

  Detectors operating on this principle are currently used only 10 in very small numbers in research or measurement laboratories, and for gas production rates much higher than those concerning

  petroleum stoves. They have no known industrial application.

  The plaintiff had to solve several problems to adapt this detector to this new industrial application and in particular: to design a specific measurement circuit, - to define a discrimination procedure between CO2 and another element

  gaseous which would have a thermal conductivity very close to that of CO2.

  This industrial application is not limited to petroleum stoves, it can be generalized to all fuel combustion heaters

solid, liquid, gaseous.

  The invention will be better understood using the following description given in

  reference to the single appended figure which is a functional diagram of the device

according to the invention.

  The device shown by way of nonlimiting example mainly comprises an actuator (10) controlled by an electronic control assembly (B) (with its microprocessor), a detection assembly (C) (with its gas sensor A) , a discrimination unit (D), a power source and a manual stop (11). In the specific application of the oil stove, the actuator

(10) is a wick actuator.

  A gas sensor (A), measuring the thermal conductivity of gases, generally consists of a resistive heating element (3) deposited by known techniques of microelectronics on a thin membrane electrically insulated and

  thermally, a temperature sensor (4) deposited on a silicone support.

  The measurement results from the thermal dissipation of the membrane, itself resulting from the thermal conductivity of the gas surrounding said membrane. For application to petroleum stoves and other types of stoves, the sensor (A) is associated with a specific circuit to form the detection assembly (C) operating as follows: The heating element (3) is activated by electronics (1), the temperature sensor (4) reads the thermal conductivity value of the gas using a bridge

  Wheatstone (5) associated with an amplifier (2).

  When the gas content detected by (A) reaches a predetermined threshold considered dangerous, the electronic assembly (B) controls the actuator (10) and

  this fact causes the stove to stop.

  Thus the stove stops each time the threshold is reached, whether the gas is CO2, or a mixture of gases or a gaseous element such as ammonia whose

  conductivities would be very close to those of CO2.

  If we want to eliminate stops that are not due to dangerous C02 releases, we will add to the device a discrimination set (D) managed by the microprocessor (8) of the control set (B), and which can operate according to various criteria such as recognition of other gases, such as: - ammonia, - nitrogen, - solvents, 2 5 - alcohol,

- etc ...

  The control assembly (B) includes other elements, for example

  example a temperature detection (9) which can be used to thermostate the device.

  In addition, an action on a push button (11) must be mandatory to start the stove, and an electronic module (7) monitors the state of the source.

supply (6).

  The advantages of the invention are as follows: - direct measurement of the rate of C02 in the room (excellent correlation with combustion), perfect compliance with decree n * 92-1280 of 10/12/92 and with standard NF D - 300, - device cannot be used in the event of energy failure

  auxiliary even with an external ignition (matches ...).

Claims (5)

  1. Safety device for a heating appliance with solid, liquid or gaseous fuel, the combustion of which it is desired to stop as soon as a predetermined rate of dangerous or unwanted gas is reached in the environment of the appliance, characterized in that it comprises a detection assembly (C) mainly composed of a sensor (A) measuring the thermal conductivity of the gases. 2. Safety device according to the preceding claim, characterized in that the sensor (A) comprises a heating element activated by electronics (1) and a temperature sensor (4) mounted in a Wheatstone bridge (5) associated with a amplifier (2).   l0 3. Safety device according to any one of claims 1 to 2,   characterized in that it further comprises a set of discrimination (D) making it possible to distinguish a production of CO2 from a gas production having   a thermal conductivity close to that of CO2.   4. Safety device according to any one of claims 1 to 3,   characterized in that it further comprises a push button (1 1) whose action is   mandatory to start the stove.   5. Safety device according to any one of claims 1 to 4,   characterized in that it further comprises a temperature detector (9) serving to thermostate the appliance.