CN1118694C - Thermometric sensor chain - Google Patents

Abstract

The present invention relates to a temperature measurement device belonging to the temperature measurement field; a sensor chain is composed of n (n>=1) resistance type temperature sensors and n+2 core cables by a specific method and is connected with a signal detection circuit composed of a multi-path simulation switch, a self-balancing bridge and a differential amplifier; a temperature signal corresponding to any temperature sensor can be gated and detected from the self-balancing bridge. As a case, the simulation signal passes through an A/D converter; codes of the multi-path simulation switch are provided by a single-chip computer and the corresponding temperature valve is calculated; temperature data can be delivered to an LED data tube for display or can be delivered to a host personal computer for storage and display by an RS232 interface.

Description

Thermometric sensor chain

The invention belongs to a kind of temperature measuring equipment in the thermometric field.

All need to carry out thermometric in fields such as industry, agricultural, scientific researches with resistor-type temperature sensor chain.Utility model patent CN.93215775.0 introduction according to State Patent Office's announcement, each thermosensitive resistance type temperature sensor respectively carries the long shielded cable of a 50m in the seawater temperature sensor chain, 32 temperature sensors have 32 cables, and it is considerable to merge together quantity.And each sensor has a constant current source power supply separately, and the temperature signal that the thermistor reflection is obtained changes voltage signal into and transmits.From the introduction of this patented technology, have two problems not solve well: each temperature sensor is with a shielded cable separately in (1) sensor chain, and the signal wire of every cable is more than 3 cores.Using under the more condition of number of sensors like this, cable seems that too much cost increases, and uses also inconvenient; (2) each thermosensitive resistance type temperature sensor is joined the power supply of one road constant-current source circuit separately, and this method is complex structure both, again the influence of transmission line resistance is incorporated in the temperature signal.Such design philosophy is to eliminate the temperature measurement error that transmission line resistance is introduced automatically by electronic circuit.If the temperature measurement accuracy by hardware or each sensor of software calibration just can not elongate or shorten the length of cable arbitrarily later again, otherwise temperature measurement error is increased.

The objective of the invention is to propose a kind of thermometric sensor chain of forming by polycore cable, multiway analog switch, self-balancing bridge, the differential amplifier of a plurality of resistor-type temperature sensors, a total shielding of band.This sensor chain need be at the inner additional any electronics translation circuit of temp probe, and temperature signal transmits the influence that is not subjected to transmission line resistance.If the individual temperature sensor of n (n 〉=1) is arranged in the sensor chain, then only need the cable of the total shielding of band of a n+2 core.Thereby solved existing problem in the prior art.

The technical solution adopted in the present invention is that it comprises by multiway analog switch, self-balancing bridge, differential amplifier, the n+2 core cable of a n resistor-type temperature sensor and a total shielding of band is formed, wherein the cable of a n sensor and a n+2 core constitutes the fore-end of sensor chain, its output terminal and multiway analog switch, self-balancing bridge is connected in the following manner with differential amplifier, the output terminal that the n bar is connected to the heart yearn of temperature sensor at an arbitrary position links to each other with the input end of multiway analog switch, and the public output of analog switch links to each other with an arm of self-balancing bridge; The other end of this n bar heart yearn is with connecing a bit as common point, also drawing a core balanced line from this common point links to each other with another arm of self-balancing bridge with a core ground wire balanced line, ground wire links to each other with the circuit ground of differential amplifier, and differential amplifier can detect from electric bridge and the corresponding temperature signal output of gating sensor.

The invention has the advantages that in its sensor chain and except that temperature sensor, cable, not to be with other any electronic devices and components.Electronic circuit belongs in the sensor chain each sensor in instrument container public.This thermometric sensor chain instrument that debugging is good, under the condition that does not change software and hardware in the instrument, the cable length of sensor chain can change in several kilometer range and can not influence the good temperature measurement accuracy of original calibration.Such sensor chain is simple in structure, and is reliable and stable, easy to use and maintenance.

Fig. 1 is a system block diagram of the present invention;

Fig. 2 is the electrical schematic diagram of sensor chain among the present invention and signal deteching circuit;

Fig. 3 is the equivalent electrical circuit that a certain sensor inserts self-balancing bridge in the sensor chain.

Further specify the example of the actual experiment of a principle of work of the present invention and a success now in conjunction with above-mentioned each accompanying drawing.

The present invention is made up of following two major parts:

1. sensor chain 1, and its total n (n 〉=1) resistance type sensor and a n+2 core cable are formed by connecting.

2. temperature signal testing circuit, it is made up of multiway analog switch 2, self-balancing bridge 3, differential amplifier 4.

Fig. 2 is temperature sensor chain and signal deteching circuit schematic diagram.Dotted line below is the structure principle chart of sensor chain, and it is identical that n resistor-type temperature sensor is serially connected in specification respectively, but in the different n core signal wire in position, n root signal wire end meets 1 D altogether, also draws two lines from the D point and is respectively L _gAnd L _g, L _gBe the equalizing contactor that connects another arm of electric bridge, L _gBe the ground wire that is connected to simulation ground AG, D point current potential is along with l _gConductor resistance change.Analog switch K ₁K _nWhich closure the sensor number sign indicating number of being sent by single-chip microcomputer decides.Because analog switch has the conducting resistance about 50 Ω, in order to make electric bridge two arm balances, so on another arm of electric bridge, be connected in series the analog switch K of a same model equally _p, and be in normally on.

Equivalent electrical circuit when certain number sensor inserts self-balancing bridge in the sensor chain is as shown in Fig. 3 frame of broken lines, R ₁Be the conductor resistance of every signal wire in the cable, because L _pBe the lead with signal wire equal length, same size, so conductor resistance is similarly L _L, R _gBe ground wire L _gResistance, R _tBe the resistor-type temperature sensor.

Transistor VT ₁With subsidiary component R ₁, R ₂, Z ₁Constitute constant-current source circuit, steady current I is provided for following electric bridge _s, the electric current that flows through the every arm of electric bridge is $I_0=\frac{1}{2}{I}_s.$ R in the electric bridge ₃=R ₄, operational amplifier A ₁And subsidiary component capacitor C ₁, C ₂, diode D ₁Constitute the differential type integrator, the output controlling filed effect transistor VT of integrator ₂The conducting degree, till the A of electric bridge point and B point voltage approximately equal.Owing on electric bridge AD and BD two arms identical resistance R is arranged all _OnAnd R ₁So, VT ₂Conduction voltage drop just in time equal R _tThe voltage at two ends.So just the temperature signal that the resistor-type temperature sensor away from electric bridge is reflected to is from VT ₂Embody in the pressure drop at two ends.As shown in Figure 2, use operational amplifier A ₂, A ₃Constitute emitter follower, operational amplifier A ₄And resistance R ₅-R ₈Constitute differential amplifier, like this from operational amplifier A ₄The voltage V of output _tBe R _tBoth end voltage is amplified the voltage after K times, and its satisfies following equation

V _t=KI ₀R _t(1) R in the formula (1) _tCan be thermistor, a quasi-resistance type sensor such as platinum resistance, hypothesis selects for use thermistor to make temperature sensor now, then thermistor R _tCan be similar in order to the following formula subrepresentation

R _t=R ₀e ^B/T(2) R in the formula ₀, B is constant, T is an absolute temperature, then has with (2) substitution (1)

V _t=KI ₀R ₀e ^B/TBoth sides are put in order after taking from right logarithm, and are converted into Celsius thermometric scale from absolute temperature scale (ATS), then have $T=\frac{B}{A+\mathrm{LN}\left(V_t\right)}-273........\left(3\right)$

A=-LN (KI ₀R ₀) (4) by current common digital measuring method, can be with V _tGive A/D transducer, the A/D transformation result is read in the back by one-chip computer and is calculated to be temperature value T according to formula (3), send LED to show then on the one hand, gives PC by the RS232 interface on the other hand and is recorded on the hard disk, is presented on the monitor.The sample signal of that number sensor, it sends the corresponding analog switch of sensor number sign indicating number gating by single-chip microcomputer and realizes.

Clearly, above-mentioned principle is not limited only to the resistor-type temperature sensor, and is suitable too for the resistance type sensor of any other physical quantity.

As the example of an enforcement of the present invention, be described in detail manufacturing process and the test result of utilizing the present invention to develop ocean temperature survey sensor chain below.

According to the design concept of foregoing invention, as temperature sensor, the cable that transmits signal is that a length overall is 60 meters with 20 thermistors, 22 core cables of the total shielding of band.Constant current I in the self-balancing bridge _sThe enlargement factor K=9 of=0.1mA differential amplifier.Resistance R when thermistor factory generally provides T=25 ℃ _tWith the B value.The R of 20 thermistors using in this example _t=5.1K Ω+10%, B=3600K+10%.Utilize this two known parameters that provide, can obtain R according to formula (2) ₀, thus can be in the hope of constant A=LN (9 * 0.1 * 10 in the formula (3) ^-4* R ₀).Differential amplifier detects temperature signal V from self-balancing bridge _t, be quantified as digital signal through behind the A/D, read in the back by single-chip microcomputer and calculate corresponding temperature value according to formula (3).

From formula (3) as can be seen, corresponding to each thermosensitive resistance type temperature sensor one group of constant A and B are arranged all, 20 thermistors have 20 groups of such constants.These 20 groups of constants leave among the EPROM of single-chip microcomputer, and single-chip microcomputer is searched corresponding constant calculations and gone out temperature value according to the sensor number sign indicating number of gating analog switch.

After ocean temperature survey sensor chain is succeeded in developing, carried out measurement correctness calibrating at national marine test satellite location Shanghai substation, measurement range 0-40 ℃ (because ocean temperature is only in this scope), temperature measurement error≤0.05 ℃.

Claims (1)

1. thermometric sensor chain, it is characterized in that it is by multiway analog switch, self-balancing bridge, differential amplifier, the n+2 core cable of a n resistor-type temperature sensor and a total shielding of band is formed, wherein the cable of a n sensor and a n+2 core constitutes the fore-end of sensor chain, its output terminal and multiway analog switch, self-balancing bridge, differential amplifier connects in the following manner, the output terminal that the n bar is connected to the heart yearn of temperature sensor links to each other with the input end of multiway analog switch, and the public output of analog switch links to each other with an arm of self-balancing bridge; The other end of this n bar heart yearn is with connecing a bit as common point, also draw a core balanced line and a core ground wire from this common point, balanced line links to each other with another arm of self-balancing bridge, ground wire links to each other with the circuit ground of differential amplifier, and differential amplifier can detect from electric bridge and the corresponding temperature signal output of gating sensor.

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