CN101629928B - Circuit structure for collecting sensor signal of catalytic combustion type fuel gas - Google Patents

Abstract

The invention relates to a circuit structure for collecting the sensor signal of catalytic combustion type fuel gas, which comprises two independent single-end signal collecting circuits. The independent single-end signal collecting circuits are two A/D converters or two electronic switches and an A/D converter; digital interfaces of the A/D converters are connected with a first single chip microcomputer, and an analog interface is respectively connected with two output ends of fuel gas sensors; the two electronic switches and the A/D converter are accommodated in a second single chip microcomputer or an independent single/ multiple A/D integrated circuit chip, the second single chip microcomputer controls the selection of the two electronic switches through an address line; one end of each electronic switch is respectively connected with two output ends of the fuel gas sensors, and the other end of the electronic switch is connected with the A/D converter. The invention has the advantages of judging the true null shift amplitude and the property of the sensors in time for corresponding treatment and realizing complete number automatic zero set.

Description

A kind of circuit structure for collecting sensor signal of catalytic combustion type fuel gas

Technical field

The present invention relates to a kind of signal acquisition circuit, especially a kind of circuit structure for collecting sensor signal of catalytic combustion type fuel gas.

Background technology

The industry that catalytic combustion type fuel gas sensor (being called for short afterwards sensor) is applied to refine oil, chemical industry, medicine, metallurgy etc. need the continuous monitoring inflammable gas, maturation, the stability of possessing skills better, the advantages such as lower, the broad spectrum activity (responsive to multiple inflammable gas) of price, in ensureing the relevant industries safety in production, obtain widespread use.

Its principle is: take circuit shown in Figure 1A as example, sensor is by the resistance 1ARC among the figure, 1ARD, 1AR1, the resistance bridge that 1AR2 forms consists of, resistance 1AR1 wherein, 1AR2 is the resistance that stability is better and nominal value equates, resistance 1ARC, 1ARD is same material, wire diameter, the platinum resistance that is sphere-like of technique coiling and selected pairing, it is detecting element (outward appearance is black and also is black element) that resistance 1ARD surface scribbles palladium catalyst, resistance 1ARC is compensating element, (therefore be not coated with catalyzer be white in color also claim white element), and both resistances and temperature coefficient equate under the normality.During normal operation, the voltage source among Figure 1A or current source POWER are heated to resistance 1ARC, 1ARD the red heat state of hundreds of ℃, and during resistance 1ARD contact inflammable gas, violent oxidation reaction (flameless burning) occurs on its surface, make resistance become large; And resistance 1ARC state remains unchanged (because of catalyst-free), and electric bridge just has signal voltage output, has realized the detection to inflammable gas.

Owing to reasons such as material, fabrication errors, the impossible full symmetric of resistance 1ARC and 1ARD and 1AR1 and 1AR2, the impact of environmental temperature fluctuation can not full remuneration, the change in resistance that adds the gravity long term to make the resistance 1ARD, the 1ARC that are in the red heat state produce deformation and cause, and the fluctuation of heating power supply POWER1A performance, the zero point drift of sensor is inevitable.

Formation, advantage and the limitation of existing sampling/automatic zero set (AZS) circuit:

Existing method is shown in Figure 1A or Figure 1B, and circuit shown in Figure 1A is made of operational amplifier 1AN1, the AD converter 1AN2 and the single-chip microcomputer 1AN3 that connect successively, Figure 1B roughly the same, to be hardware aspects be as good as with traditional sample circuit characteristics, need not increase the hardware input.When Flammable Gas Detector or transmitter put into operation, through manually potentiometer tentatively being returned to zero (described potentiometer also may be digital potentiometers), just differentiated according to the different qualities of drift and combustible gas signal (the general per minute of combustible gas signal change tens of units and drift common per a few hours changed one to two unit to tens of hours) by Single Chip Microcomputer (SCM) program later on and carried out corresponding processing (contain drift such as judgement and just deduct first wherein drift value).The problem that exists is: because AD converter and single-chip microcomputer are connected to the back of differential amplifier 1AN1 in turn, eliminated the original level value in the signal that obtains, so true level that can not two output terminals of detecting sensor, it is the true zero point that single-chip microcomputer be can not determine sensor, (its " automatic zero set (AZS) " just carries out the plus-minus of numeral in single-chip microcomputer 1AN3, really do not eliminate the drift of sensor) thereby can't determine progressivity drift and total drift amplitude, single-chip microcomputer " has been hoodwinked ".After total drift reaches certain amplitude, the response of sensor can present larger non-linear, so that measurement result substantial deviation actual value, have certain potential safety hazard (its security is not even such as the traditional circuit without automatic zero set (AZS)), this just automatic zero set (AZS) technology obtains enough theoretical main causes of supporting so far in the application in this field.

Explanation about drift character:

1, the symmetry drift refers to determine up and down drift of fluctuation of point around certain, such as the round the clock variation of temperature and cause the corresponding drift of sensor; The drift that seasonal variety take year as unit temperature causes is as the same, it is characterized in that range of drift is no more than definite maximal value.

2, the progressivity drift refers to drift unidirectional and that add up in time, such as the drift that makes the silk material of black-and-white component deform and cause owing to action of gravitation for hard-wired sensor, its range of drift is unrestricted and can't pre-determine, thereby more dangerous.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of circuit structure for collecting sensor signal of catalytic combustion type fuel gas is provided, it can be judged drift of different nature and give corresponding processing, thereby in time find potential safety hazard, significant for the equipment of guaranteeing relevant industries and personal security; The cost aspect only needs a small amount of increase even may reduce.

According to technical scheme provided by the invention, described circuit structure for collecting sensor signal of catalytic combustion type fuel gas comprises two independently single-ended signal Acquisition Circuit;

Described two independently the single-ended signal Acquisition Circuit be two road A/D converters, or be two electronic switches and one road A/D converter;

The digital interface of described two road A/D converters is connected with the first single-chip microcomputer, and analog interface connects respectively two output terminals of combustible gas sensor;

Described two electronic switches and one road A/D converter are that second singlechip inside comprises, or are multi-channel A/D integrated circuit (IC) chip independently, and described second singlechip is through the selection of two electronic switches of address wire control; Described two electronic switch one ends connect respectively two output terminals of combustible gas sensor, and the other end connects described one road A/D converter.

Described two independently the single-ended signal Acquisition Circuit connect respectively two output terminals of combustible gas sensor by filtering circuit.

Advantage of the present invention is:

1, in time the real drift amplitude of determine sensor and character thereof eliminate safe hidden trouble in order to process accordingly.

2, can realize completely digital automatic zero set (AZS), reduce production/debugging work load.

3, the cost increase does not seldom perhaps increase even reduces.

Description of drawings

Figure 1A is a kind of circuit structure diagram of prior art.

Figure 1B is the second circuit structure diagram of prior art.

Fig. 2 A is the structural representation of the present invention that consists of with two road AD chips and single-chip microcomputer.

Fig. 2 B is for adding the structural representation of the present invention that single channel AD chip and single-chip microcomputer consist of with the two-way electronic switch.

Fig. 3 A is the circuit diagram of the present invention that consists of with two-way AD chip AD7782 and single chip computer AT 89S51.

The of the present invention circuit diagram of Fig. 3 B for consisting of with the single-chip microcomputer SN8P1909 that includes multi-channel A/D.

Embodiment

The invention will be further described below in conjunction with drawings and Examples.

Shown in Fig. 2 A, two output terminal O2A and the S2A of sensor are connected to high-resolution AD converter 2AN1 and 2AN2 by filtering circuit respectively, and single-chip microcomputer 2AN3 is sent in the output of AD converter 2AN1 and 2AN2.

If: the current potential that O2A is ordered is Vo

The current potential that S2A is ordered is Vs

Ideally, 2AR1=2AR2, Vs-Vo=0, sensor complete equipilibrium.Actual conditions are that the sensor (be generally 5～7 day) aging through the front continuous energising of dispatching from the factory tends towards stability in the scene of putting into operation switched on 5 minutes.Because the apolegamy precision of 2AR1,2AR2 is higher, symmetry and hot tracing property are better, can think that the Vo of this moment namely is the true zero-bit of sensor, and the Vs-Vo of this moment are initial imbalance, for the good sensor black-and-white component of apolegamy, even its numerical value is very little of zero.In the operating temperature range of sensor, zero point drift amplitude (maximum temperature is floated) is determined, it is dangerous that remarkable drift greater than this amplitude is considered to, when progressivity drift or total drift reach certain amplitude (substantial deviation is initially lacked of proper care), single-chip microcomputer just sends alerting signal, and prompting the related personnel in time process.In a word, single-chip microcomputer is monitored the variation of Vo, Vs and Vs-Vo, at any time unusual circumstance always.

Following some explanation is arranged:

1, for to avoid possible false alarm, 1.3～1.5 times that desirable maximum temperature is floated on (according to the quality of sensor quality) engineering as alarm threshold value.

2, to the requirement of AD chip, consider from cost and aspect of performance, than better suited be low-cost and high-precision AD chip, for example sigma-delta type or multiple integral type require resolution more than 16bit.

3, for reducing cost, preferentially select monolithic hyperchannel AD chip, as select the single-chip microcomputer cost performance that includes multi-channel A/D higher.

4, many monolithic multi-channel A/D chips and the singlechip chip that includes multi-channel A/D in fact inner related circuit structure be multi-channel electronic switch and add single channel AD, only be reflected on the external characteristic quite similar with the multi-channel A/D chip.

5, the signal of sensor output terminal all gathers by same AD chip among Fig. 2 B, is just controlled the selection of electronic switch SW0, SW1 through address wire A0, A1 by single-chip microcomputer 2BN2.Two kinds of circuit structures of Fig. 2 A and Fig. 2 B are equivalent in addition.

6, consist of an inflammable gas detection system or transmitter, usually also have demonstration, warning and output, because of and the technology of the present invention aspect without direct correlation, so accompanying drawing with discuss in all do not relate to.

The below enumerates two specific embodiments, and Fig. 3 A is the circuit diagram of the present invention that consists of with two-way AD chip AD7782 and single chip computer AT 89S51.The of the present invention circuit diagram of Fig. 3 B for consisting of with the single-chip microcomputer SN8P1909 that includes multi-channel A/D.All do not draw the conventional additional device of said chip among Fig. 3 A, Fig. 3 B.

As shown in Figure 3A, take serial output sigma-delta type two-channel 2-4 4bit AD chip 3AN1 model as AD7782 as main formation sample circuit.The positive input terminal of two passages of chip 3AN1 meets respectively two output terminal O3A and the S3A of sensor; be connected to respectively low-pass filtering-clamping circuit therebetween; with the antijamming capability that strengthens system and the input end of protecting 3AN1, the negative input end ground connection of two input channels of 3AN1 (do not omit among the figure and draw).Described low-pass filtering-clamping circuit has two, one comprises: the first electric capacity 3,AC1 one end ground connection one end connects the 3rd resistance 3AR3, and the 3rd resistance 3AR3 other end connects respectively the first diode 3AD1 positive pole, the 5th resistance 3AR5 and passes through the 3rd electric capacity 3AC3 ground connection; It two comprises: the second electric capacity 3,AC2 one end ground connection one end connects the 4th resistance 3AR4, and the 4th resistance 3AR4 other end connects respectively that the second diode 3AD2 is anodal, the 6th resistance 3AR6 and by the 4th electric capacity 3AC4 ground connection.

The negative pole of described the first diode 3AD1 and the second diode 3AD2 is all by stabilivolt 3AN2 ground connection, connect power supply by the 5th electric capacity 3AC5 ground connection with by the 7th resistance 3AR7.The model of stabilivolt 3AN2 is LT1634B2.5.

The RANGE of chip 3AN1 and MODE end all connects power supply, and the gain of namely selecting inner PGA is 1 and changes with passive mode.The data output end Dout of chip 3AN1, clock end SCLK, sheet choosing end CS and channel selecting end CH1/CH2 connect respectively P1.0, P1.1, P1.2 and the P1.3 end that chip 3AN3 model is AT89S51.The parallel fiducial chip LT1634B2.5 of high precision 2.5V (being stabilivolt 3AN2) provides the leakage path of the required reference voltage of chip 3AN1 and clamp diode (the first diode 3AD1, the second diode 3AD2).The 3rd resistance 3AR3, the 4th resistance 3AR4 metalfilmresistor, the first electric capacity 3AC1, the second electric capacity 3AC2 be with CC41 high-frequency ceramic electric capacity, and the 3rd electric capacity 3AC3, the 4th electric capacity 3AC4, the 5th electric capacity 3AC5 are with MKP (being domestic CBB) material electric capacity.Chip 3AN3 model is that AT89S51 belongs to typical 51 series monolithics, and its Resources on Chip no longer describes in detail.

Transformation result is Code=2 ²³* ((Ain/2.56)+1);

Ain is the current potential amount of sensor output terminal.

The sample circuit of Fig. 3 B for consisting of as the master as SN8P1909 take the OTP type single-chip microcomputer 3BN1 model that includes multi-channel high-resolution AD.Single-chip microcomputer SN8P1909 includes programmable amplifier (PGA), digital filter (DFM), 16bit AD converter etc., except common parallel port Parallel port, also have serial port Serial port and LCD driving circuit SEG0-SEG31, have very high cost performance when needing at the same time to sample multichannel analog signals and driving LCD liquid crystal display.Only used two analog channel A1 and the A2 of single-chip microcomputer SN8P1909 among Fig. 3 B, (resistance 3BR3, electric capacity 3BC1 and resistance 3BR4, electric capacity 3BC2) is simple than Fig. 3 A for the low-pass filter circuit of input end, and time constant is also less.This is the DFM better performances that includes owing to SN8P1909, adds the effect of the 8th resistance 3BR8, the 9th resistance 3BR9, the 6th electric capacity 3BC6, and antijamming capability own is quite good.The 8th resistance 3BR8, the 9th resistance 3BR9 are connected to respectively AO+ and the AO-end of single-chip microcomputer SN8P1909, and connect respectively the two ends of the 6th electric capacity 3BC6; The 6th electric capacity 3BC6 connects the X+ end that the 8th resistance 3BR8 end connects single-chip microcomputer SN8P1909; The 6th electric capacity 3BC6 connects the X-end that the 9th resistance 3BR9 end connects single-chip microcomputer SN8P1909.Single-chip microcomputer SN8P1909 contains reference source in inside, but performance is good not, thus provide a stable 1.25V outside reference with stabilivolt 3BN2 model for LT1634B1.2, thus guarantee the precision of AD conversion.The gain of inner PGA is 1 by software set, and channel selecting is also undertaken by software, and CHS 000,001 has namely chosen the difference input mode of two passage A1, A2 (actual is the inner V of negative input termination _ACM, inside is difference, be reflected to be equivalent on the external characteristics single-ended).Identical in the effect of diode 3BD1,3BD2 and Fig. 3 A corresponding device, resistance 3BR3,3BR4,3BR8,3BR9 use metalfilmresistor equally, and electric capacity 3BC1,3BC2,3BC3,3BC4,3BC5,3BC8 are with the electric capacity of MKP material.The shortcoming of this scheme is that order set and common 51 series of SN8P1909 are incompatible.

Transformation result is Code=± 31250* (Ain/1.25);

Ain=Vo-V _ACMOr Vs-V _ACM, Ain＞V _ACMTime is+, otherwise be-.

In Fig. 3 B, because A1-, A2-, VR-is equal links to each other with ACM, and the 1.2V of ACM and chip internal joins, so the current potential of A1-, A2-, VR-and ACM is 1.2V, its respective value is 30000, and the real potential respective value is:

30000±31250*(Ain/1.25)。

Claims (1)

1. a circuit structure that is used for collecting sensor signal of catalytic combustion type fuel gas is characterized in that: comprise two independently single-ended signal Acquisition Circuit;

Described two independently the single-ended signal Acquisition Circuit be two road A/D converters (2AN1,2AN2), or be two electronic switches (SW0, SW1) and one road A/D converter (2BN1);

The digital interface of described two road A/D converters (2AN1,2AN2) is connected with the first single-chip microcomputer (2AN3), and analog interface connects respectively two output terminals of combustible gas sensor;

Described two electronic switches (SW0, SW1) and one road A/D converter (2BN1) comprise for second singlechip (2BN2) inside, or being multi-channel A/D integrated circuit (IC) chip independently, described second singlechip (2BN2) is through the selection of address wire two electronic switches of control (SW0, SW1); Described two electronic switches (SW0, SW1) end connects respectively two output terminals of combustible gas sensor, and the other end connects described one road A/D converter (2BN1);

Described two independently the single-ended signal Acquisition Circuit connect respectively two output terminals of combustible gas sensor by filtering circuit.

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