Background technology
The statement of this part only provides the background information relevant with the present invention, and does not constitute prior art.
Concerning many application, the existence that detects inflammable gas or chemical constitution is very important, for example comprises, whether the concentration that detects inflammable gas has surpassed inflammable boundary.
There is the different combustible gas sensor system of many kinds can both be used for detecting the existence and the concentration of inflammable gas in the techniques known in the art.For example, sensing system, optical sensor system and the saw sensor system that surveys conductivity can both use.
(conductiometric) sensor of one type survey conductivity is polymkeric substance-absorption process chemical resistance sensor.Polymkeric substance-absorption process chemical resistance sensor comprises sensor probe and the sensing element with pair of electrodes.This probe is the part of sensor circuit.Usually, the form taked of this sensing element is the polymerization sensor film across two electrodes.Sensor film is exposed in the surrounding air.The accurate composition of polymerization sensor changes according to inflammable gas, so that sensor film can absorb inflammable gas when it is exposed in the surrounding air.
In being exposed to inflammable gas and when absorbing inflammable gas, sensor film expands and the experience volume change.The variation of volume causes the changes in resistance of this film, and this changes in resistance can be measured by electrode.
Typically processor or control module are coupled to sensor circuit.The resistance of processor monitoring sensor film with determine inflammable gas whether exist with and concentration.Processor can be coupled to user interface.Typically, this user interface comprises an indicating device that produces signal when combustable gas concentration surpasses predetermined threshold.
Yet the resistance of sensor film not only changes according to the absorption to inflammable gas, also can change according to the variation of environment temperature.If sensor film has positive temperature-coefficient of electrical resistance, the resistance of sensor film can increase along with the rising of environment temperature.If sensor film has negative temperature-coefficient of electrical resistance, the resistance of sensor film can reduce along with the rising of environment temperature.It still is that negative temperature coefficient depends on the composition of sensor film and its operating position that sensor film has positive temperature coefficient (PTC).
Because the detection of inflammable gas is based on variation that the resistance of sensor film when sensor absorbs inflammable gas takes place, so cause that the variation of ambient temperature of sensor film changes in resistance can accurately detect the ability that inflammable gas exists to sensing system and bring negative effect.For example, if sensor film has positive temperature-coefficient of electrical resistance and resistance increase when absorbing inflammable gas, then the rising of environment temperature may cause sensing system to generate a rub-out signal, and there is inflammable gas in indication when not having inflammable gas.
Typical chemical resistance sensor is along with the aging meeting of time causes the skew of its performance, particularly when the chemical resistance sensor is subjected to the influence of temperature cycle variation.Under temperature and aging common influence, the chemical resistance sensor can not accurately detect existence and its concentration of inflammable gas.
Embodiment
Below description in fact be exemplary, do not limit of the present invention open, use or use.
Accompanying drawing 1 has been described the critical piece of an exemplary chemical resistance sensing system 10 generally.Sensing system 10 mainly comprises chemical resistance sensor probe 12, control module 14 and user interface (interface) 16.Sensor probe 12 comprises temperature compensating element 20.
Sensor probe 12 interacts with external environment condition 17 and detects the existence of interested chemical constitution or inflammable gas 18.Sensor probe 12 is based on to the lasting detection of the inflammable gas in the external environment condition 17 18 and generate original output signal 19a.Control module 14 is handled original output signal 19a.Output 19b after control module 14 will calculate sends user interface 16 to, with transfer to analysis from the original output signal 19a of sensor probe 12.Control module 14 can provide operational order and electric energy to probe 12, for example, all represents by 22.
User interface 16 provides information about the state of sensing system 10 to the user, and for example whether system 10 detects the existence of inflammable gas 18.User interface 16 can be the various multi-form of the computer demonstration from a simple alerting signal to complexity well known in the art.
Sensor probe 12 can adopt the form of multiple different sensor probe.For example, the form that adopts of sensor probe 12 can be that exercise question is any one in the sensor probe described in the 7th, 113, No. 304 United States Patent (USP)s of " durable chemical resistance sensor (Robust Chemiresistor Sensor) ".Sensor probe 12 can comprise the sensor element or the film of conduction, and it absorbs inflammable gas 18 and change resistance when absorbing inflammable gas.Sensor film can be any suitable sensor film as known in the art, for example the number of patent application of application on April 11st, 2003 is NO.10/411,805 exercise question those sensors for describing in " gas sensor and its used material (VaporSensor and Materials Therefor) " United States Patent (USP).The full content of incorporating these patents herein into as a reference.
With reference to the accompanying drawings 2, show the exemplary electrical circuit block diagram sketch of a sensor probe 12, totally represent with 30.In the present embodiment, sensor probe 12 comprises a sensing element and a temperature compensating element that exists with second resistor, 32 forms that exists with first resistor, 31 forms.First and second resistors 31 and 32 are electrically connected in series, to form bleeder circuit.First resistor 31 be exposed to inflammable gas wherein existence and or combustable gas concentration want in the monitored surrounding environment, and the resistance of first resistor 31 is subjected to the influence of the existence of inflammable gas.Second resistor 32 is isolated with the surrounding environment that will monitor, and the resistance of second resistor 32 is not subjected to the influence of inflammable gas when inflammable gas exists.Therefore, second resistor 32 is determined the influence of inflammable gas to first resistor 31 as the reference element.Preferably, second resistor 32 is isolated by coating, coverture or shell and the surrounding environment that will monitor.
In the whole disclosure, term " exposure " or " being exposed in the surrounding environment " refer to a component exposed in the airborne such a case that will monitor the peripheral environment that wherein whether has inflammable gas, and term " isolation " or " isolating with surrounding environment " refer to following this situation, the air insulated of parts and the external environment condition that will monitor wherein, thereby isolate with presumable inflammable gas in this environment, but can't not be subjected to influence of temperature variation in the environment.
The output voltage of sensor probe 12 equals the voltage drop on first resistor 31.Exist under the situation of inflammable gas, be exposed to first resistor 31 of external environment condition, with respect to second resistor 32 change resistances (its with surrounding environment so that with the inflammable gas isolation), cause the voltage drop on first resistor 31 to change.Signal corresponding to this voltage drop is sent to control module 14, with the existence and/or the concentration of indication inflammable gas.
First resistor 31 and second resistor 32 have similar characteristic, particularly similarly and the characteristic of temperature correlation.Preferentially, first resistor 31 has similar or identical temperature-coefficient of electrical resistance α with second resistor 32, and therefore first resistor 31 and second resistor 32 change their resistance in a similar fashion according to temperature variation and cyclical variation.
Particularly, sensor probe 12 is in temperature T
1Output voltage V
Out(it equals the voltage drop on first resistor 31) can be described as:
Here, V is the voltage that is applied on the circuit 30, and R1 and R2 are respectively first resistor 31 and the resistance value of second resistor 32 when temperature T 1.
When ambient temperature rising Δ T (from T
1To T
2) time, the resistance of resistor 31 changes to R1 (1+ α Δ T) from R1, and the resistance of second resistor 32 changes to R2 (1+ α Δ T) from R2, and wherein α is temperature-coefficient of electrical resistance and can just can bears.
The output voltage V of sensor probe when temperature T 2
OutCan be described to:
Because first resistor 31 and second resistor 32 have similar or identical and performance temperature correlation, environmental factor such as for example temperature and/or sensor be aging will cause the variation of the resistance value of first resistor 31 and second resistor 32.The result is that output voltage (that is the voltage drop at first resistor, 31 two ends) is not subjected to temperature variation and/or the aging influence of sensor.V
OutOnly in the resistance value of first resistor 31 owing to the existence of the inflammable gas Shi Caihui that changes changes, because the resistance value of second resistor 32 can not change because of the existence of inflammable gas.
With reference to accompanying drawing 3, represent with Reference numeral 40 according to the exemplary electrical circuit block diagram sketch of the sensor probe of second embodiment of the invention.Circuit 40 comprises sensing element and temperature compensating element, and they are configured to the form of bridge diagram.Sensing element comprises first resistor 41 and second resistor 42.Temperature compensating element comprises the 3rd resistor 43 and the 4th resistor 44.First resistor 41 and second resistor 42 are exposed to the existence of inflammable gas wherein and/or concentration and want in the monitored surrounding environment, and the 3rd resistor 43 and the 4th resistor 44 are isolated with surrounding environment and as reference element.This bridge diagram is preferably Wheatstone bridge, and it comprises four arms, and two arms are included in first side 50, and two arms are included in second side 52.First resistor 41 and the 3rd resistor 43 are connected in series in first side, 50, the second resistors 42 and the 4th resistor 44 is connected in series in second side 52.Each side 50 or 52 has a resistor to be exposed in the surrounding environment and another resistor and surrounding environment are isolated.The resistor of the same side has similar characteristic, particularly similar temperature correlated characteristic.The output voltage of sensor probe is the voltage drop between the mid point of both sides 50 and 52.
Particularly, the output voltage of sensor probe when temperature T 1 can be described as so following:
Wherein V is the voltage that is applied on the sensor probe 12, and R1, R2, R3 and R4 represent first resistor 41, second resistor 42, the 3rd resistor 43 and the 4th resistor 44 in temperature T respectively
1The time resistance value.
First resistor 41 is connected in the same side 50 with the 3rd resistor 43 and similar or identical temperature-coefficient of electrical resistance β is arranged.First resistor 41 and the resistance value of the 3rd resistor 43 when temperature T 2 change to R1 (1+ β Δ T) and R3 (1+ β Δ T), Δ T=T here by R1 and R3 respectively
2-T
1
Second resistor 42 is connected on same side 52 and similar or identical temperature-coefficient of electrical resistance γ is arranged with the 4th resistor 44.Second resistor 42 and the resistance value of the 4th resistor 44 when temperature T 2 change to R2 (1+ γ Δ T) and R4 (1+ γ Δ T) by R2 and R4 respectively.
Therefore, sensor probe is in temperature T
2The time output voltage can be described as so following:
Because (exposure) first resistor 41 has similar characteristic with (isolation) the 3rd resistor 43, temperature variation/cyclical variation does not influence the voltage drop at first resistor, 41 two ends of first side 50.Similarly, because (exposure) second resistor 42 has similar characteristic with (isolation) the 4th resistor 44, temperature variation/cyclical variation does not influence the voltage drop at second resistor, 42 two ends.Therefore, the voltage of the sensor probe 12 between both sides 50 and 52 mid points output V
OutKeep not being subjected to the factor affecting of temperature correlation, for example the sensing system that causes of temperature variation and temperature cycle variation is aging.Voltage output V
OutThe resistance value of two resistors in this moment bridge diagram the same side only when existing, inflammable gas just can change, because can not change in a similar manner.
Be to be understood that and recognize, in bridge diagram, only have an exposure resistor also can obtain similar compensating effect by using though in bridge diagram shown in Figure 3, there are two resistors 41 and 42 to be exposed in the surrounding environment.
By utilizing the structure of chemical resistance sensing system, temperature compensating element can compensate owing to environment temperature changes the variation that takes place the resistance value of sensing element.Therefore, the chemical resistance sensing system can be distinguished by inflammable gas and have change in resistance that causes and the change in resistance that is caused by the ambient temperature variation.Therefore, chemical resistance sensor of the present invention can detect the existence of inflammable gas 18 more exactly.
Also can realize pass through the compensation of the resistance skew that takes place along with the working time by notion of the present invention.The aging characteristics of typical chemical resistance sensing system comprise that resistance value is offset in time, particularly when the chemical resistance sensing system is subjected to the influence of temperature cycle variation.Resistor by using an isolation is as the reference element, and the influence of temperature correlation factor can be stablized and be not subjected to because of the relative person's character of sensing probe output voltage to sensor probe more.
Because the output voltage of sensing system has been made compensation by isolation resistor, so the chemical resistance sensing system does not need extra analysis software to come analysis temperature and aging effect, thereby structure is simpler.
Though the isolation resistor as temperature or compensation of ageing element is to describe in the environment of voltage divider and Wheatstone bridge circuit, but be to be understood that and recognize, under the situation that does not break away from spirit of the present invention disclosed herein, also can be used in other circuit as the isolation resistor of temperature or compensation of ageing element.
In fact this description is exemplary, thereby the variation that does not depart from order of the present invention all within the scope of the invention.This variation should not be taken as and depart from the spirit and scope of the present invention.