CN202442810U - Thermal resistor temperature measuring device - Google Patents
Thermal resistor temperature measuring device Download PDFInfo
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- CN202442810U CN202442810U CN2012200251415U CN201220025141U CN202442810U CN 202442810 U CN202442810 U CN 202442810U CN 2012200251415 U CN2012200251415 U CN 2012200251415U CN 201220025141 U CN201220025141 U CN 201220025141U CN 202442810 U CN202442810 U CN 202442810U
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Abstract
The utility model discloses a thermal resistor temperature measuring device, which is used for measuring the site temperature in an industrial environment. The thermal resistor temperature measuring device comprises a thermal resistor, a power supply circuit, a constant current source circuit, a data processing circuit and a communication interface circuit, wherein the data processing circuit comprises a voltage amplifier circuit, an analog filter circuit, an analog to digital conversion circuit and a one-chip microcomputer control circuit. The output terminal of the power supply circuit is respectively connected to the corresponding power supply terminals of other circuit modules; the output terminal of the constant current source circuit is connected to the current input terminal of the thermal resistor; the voltage signals at two ends of the thermal resistor are connected to the two input terminals of the voltage amplifier circuit; the output terminal of the voltage amplifier circuit is connected to the input terminal of the one-chip microcomputer control circuit through the analog filter circuit and the analog to digital conversion circuit in sequence; and the one-chip microcomputer control circuit is connected to the communication interface circuit in a bidirectional mode. According to the utility model, the same data processing circuit is employed to realize 2-line, 3-line and 4-line on-site temperature measure, and the thermal resistor temperature measuring device is characterized in that the structure is simple, the operation is easy, and the measure precision is high.
Description
Technical field
The utility model relates to a kind of thermal resistance temperature measuring equipment, is used to measure under the various environment, especially the scene temperature under the industrial environment.
Background technology
Thermal resistance is the primary element that converts temperature variation into resistance change; Usually need be delivered to the electric signal that the resistance two ends produce on Computer Control Unit or other primary instrument through lead-in wire; But because industrial heat resistance all is installed in the production scene; Have certain distance between itself and the pulpit, so the lead-in wire of thermal resistance has bigger influence to measurement result.
Temperature measuring equipment uses the Pt100 platinum resistance thermometer sensor, as temperature detecting resistance usually, and it has advantages such as precision height, temperature-measuring range be wide, easy to use, in industrial process control and measuring system, has obtained application widely.
When utilizing the thermal resistance thermometric, the mode of thermal resistance place in circuit has three kinds, and wherein, it is 1 that the current return of 2 line systems and voltage measurement circuit close two, low precision; The reference bit of the current return of 3 line systems and the reference bit of voltage measurement circuit are a line, if the appropriate design metering circuit can reach very high precision; The current return of 4 line systems and voltage measurement circuit independently separate, and precision is high, but takes line.Thermal resistance temperature measuring equipment at present commonly used, every kind of all corresponding different data processing circuit of the mode of connection causes the complex structure of device, uses inconvenience.
Summary of the invention
The technical matters that the utility model will solve provides a kind of simple in structure, processing ease and the high thermal resistance temperature measuring equipment of measuring accuracy, can select above any martingale according to practical situations, realizes that scene temperature measures.
For solving the problems of the technologies described above; The technical scheme that the utility model is taked is: a kind of thermal resistance temperature measuring equipment; Its key is: comprise thermal resistance, power circuit, constant-current source circuit and data processing circuit and the communication interface circuit be made up of voltage amplifier circuit, analogue filter circuit, analog to digital conversion circuit, single chip machine controlling circuit; The output terminal of said power circuit connects the corresponding power end of other circuit modules respectively; The current input terminal of the output termination thermal resistance of said constant-current source circuit; The voltage signal of thermal resistance two ends output is connected on two input ends of voltage amplifier circuit; The output terminal of voltage amplifier circuit connects the input end of single chip machine controlling circuit successively through analogue filter circuit, analog to digital conversion circuit, single chip machine controlling circuit is connected with communication interface circuit is two-way.
Above-mentioned thermal resistance is the Pt100 platinum resistance thermometer sensor.
Adopt the beneficial effect that technique scheme produced to be: the utility model employing platinum resistance thermometer sensor, Pt100 is used for the measurement of scene temperature, temperature-measuring range 0-400 ℃.The utility model is simple in structure, processing ease and measuring accuracy high, has following characteristics:
(1) the utility model adopts identical data processing circuit, without any need for the extra setting of software and hardware, can realize the platinum resistor temperature measuring of 2,3,4 line systems according to practical situations; Wherein, the mode of connection of 2 lines is used for temperature survey is required lower occasion, and 3 lines and 4 line systems can realize the measurement of degree of precision; (2) the utility model is selected the superpower anti-interference low-power scm of STC11F04E series of high speed for use, carries EEPROM; And the standard of employing MODBUS communication protocol can directly be communicated by letter with the industrial configuration software of host computer; (3) adopt the integrated instrument amplifier of AD621, realize that the precision of signal is amplified and differential-to-single-ended conversion, the problem of instrument amplifier difficult parameters of having avoided many amplifiers to constitute simultaneously to mate; (4) analog to digital converter adopts 12 A/D conversion chip ADS1286; The minimum temperature variation that can tell 0.165 ℃; If the resolution requirement to temperature in the practical application is not high; Can adopt with 10 compatible fully A/D conversion chips of its pin and realize TLC1549 replacement or 8 A/D conversion chip TLC549 replacements, and circuit need not done any change.
Description of drawings
Fig. 1 is the functional-block diagram of the utility model;
Fig. 2 is the circuit theory diagrams of the power circuit of the utility model;
Fig. 3 is the circuit theory diagrams of the constant-current source circuit of the utility model;
Fig. 4 is the data processing of the utility model and the circuit theory diagrams of communication interface circuit;
Fig. 5 is the 2 line system thermometric wiring schematic diagrams of the utility model;
Fig. 6 is the 3 line system thermometric wiring schematic diagrams of the utility model;
Fig. 7 is the 4 line system thermometric wiring schematic diagrams of the utility model;
Among the figure, 1, power circuit, 2, constant-current source circuit, 3, data processing circuit, 3-1, voltage amplifier circuit, 3-2, analogue filter circuit, 3-3, analog to digital conversion circuit, 3-4, single chip machine controlling circuit, 4, communication interface circuit; U1, single-chip microcomputer, U2, reference voltage source, U3, instrument amplifier; U4, operational amplifier, U5, analog to digital converter, U6-U7, the adjustable constant current source of three ends; U8, first voltage stabilizer, U9, second voltage stabilizer, U10, voltage reversal device; U11-U13, first to the 3rd photoelectrical coupler, U14,485 communication interface chips, U15, power isolation module.
Embodiment
Below in conjunction with accompanying drawing and embodiment the utility model is done further detailed explanation.
Be illustrated in figure 1 as the functional-block diagram of the utility model.The utility model comprises thermal resistance Rt, power circuit 1, constant-current source circuit 2 and data processing circuit 3 and the communication interface circuit 4 be made up of voltage amplifier circuit 3-1, analogue filter circuit 3-2, analog to digital conversion circuit 3-3, single chip machine controlling circuit 3-4; The output terminal of said power circuit 1 connects the corresponding power end of other circuit modules respectively; The current input terminal of the output termination thermal resistance Rt of said constant-current source circuit 2; The voltage signal of thermal resistance Rt two ends output is connected on two input ends of voltage amplifier circuit 3-1; The output terminal of voltage amplifier circuit 3-1 connects the input end of single chip machine controlling circuit 3-4 successively through analogue filter circuit 3-2, analog to digital conversion circuit 3-3, single chip machine controlling circuit 3-4 and 4 two-way connections of communication interface circuit.The utility model employing platinum resistance thermometer sensor, Pt100 is used for the measurement of scene temperature, temperature-measuring range 0-400 ℃.
Be illustrated in figure 2 as the circuit theory diagrams of the power circuit of the utility model.Power circuit 1 is made up of the first voltage stabilizer U8, voltage reversal device U10, the second voltage stabilizer U9, protection diode D3, D4, light emitting diode D8, magnetic bead L1, capacitor C 9-C12 and resistance R 18; Positive pole+the Vs of external direct current power supply is voltage+Vcc behind protection diode D3, and voltage+Vcc connects input end 1 pin of the first voltage stabilizer U8 and the second voltage stabilizer U9 respectively, and 2 pin of the second voltage stabilizer U9 connect the negative pole of external direct current power supply through protection diode D4; Output terminal 3 pin of the first voltage stabilizer U8 are+9V voltage that capacitor C 9 is connected between output terminal 3 pin and ground of the first voltage stabilizer U8; Input end 8 pin of voltage reversal device U10 connect output terminal 3 pin of the first voltage stabilizer U8; Output terminal 5 pin of voltage reversal device U10 are-9V voltage; Capacitor C 12 is connected between output terminal 5 pin and ground of voltage reversal device U10, and capacitor C 11 is connected between 2 pin and 4 pin of voltage reversal device U10; Output terminal 3 pin of the second voltage stabilizer U9 are+5V voltage; Capacitor C 10 is connected between output terminal 3 pin and ground of the second voltage stabilizer U9; Output terminal 3 pin of the second voltage stabilizer U9 are output as simulation+5VA voltage behind magnetic bead L1, resistance R 18 be connected between simulation+5VA voltage and the ground after light emitting diode D8 connects.
The utility model adopts the external direct current power supply power supply of 12-24V, and the effect of protection diode D3 and D4 is in order to prevent that power supply from connecing defective chip on the contrary; The first voltage stabilizer U8 adopts MC7809 at first to obtain+9V voltage; Utilize voltage reversal device ICL7660 general+9V voltage transformation to be-9V voltage again; Obtain like this ± the symmetrical power supply of 9V, this symmetry power supply is integrated transporting discharging and the instrument amplifier AD621 power supply in the filtering circuit; Obtaining+5V voltage through the second voltage stabilizer MC7805 simultaneously, is the digital circuit power supply of 5V, should+voltage+5VA that 5V voltage obtains through magnetic bead L1 again is the mimic channel power supply, uses magnetic bead L1 to realize the isolation of analog-and digital-power supply.Should be during the design circuit plate with simulating ground and digitally connecting together at single-point.
Be illustrated in figure 3 as the circuit theory diagrams of the constant-current source circuit of the utility model.Constant-current source circuit 2 constant current source with temperature compensation for being made up of two the three adjustable constant current source U6 of end, U7, resistance R 1, R2, R5, R6 and diode D1, D2, the steady current of its output be respectively+I ,-I.Three ends are adjustable integrated constant current source U6, U7 produce LM334 by National Semiconductor, produce the steady current of 200 μ A.The operating position of the different modes of connection and two constant current sources such as Fig. 5-shown in Figure 7.
Like Fig. 5-2 line systems, 3 line systems and 4 line system thermometric wiring schematic diagrams that are respectively the utility model shown in Figure 7.Among the figure, Rt representes the Pt100 platinum resistance thermometer sensor,, and camber line is the short circuit lead between device terminals, and r1-r4 is conductor resistance, because each segment length's lead is isometric, so r1=r2=r3=r4=r is arranged.
In the 2 line system thermometrics of Fig. 5; Platinum resistance thermometer sensor, is connected on the temperature measuring equipment far-end; The 200 μ A electric currents that flowed out by constant current source+I are that the long lead of r1 flows into platinum resistance thermometer sensor, through resistance behind+V end, are the long lead outflow of r2 from resistance; Flow back to simulation ground AGND at last ,+V and-V import the positive and negative input end of instrument amplifier U3 respectively.Circuit by Fig. 5 can know that the voltage U=I (r1+Rt+r2) at actual input instrument amplifier U3 two ends is because the resistance of platinum resistance thermometer sensor, is less; Therefore conductor resistance can't be ignored; The method make r1 and r2 very little only if lead enough is lacked, but this also can only reduce error as far as possible because the existence of wire voltage has than mistake; Can not fundamentally eliminate conductor resistance influence, and to shorten conductor lengths in a lot of occasions be unpractical.
In the 3 line system thermometrics of Fig. 6, used two constant current source+I and-I, the direction of current of these two current sources is outflow.Platinum resistance thermometer sensor, is connected on the temperature measuring equipment far-end, behind the 200 μ A electric current mistakes+V end by constant current source+I outflow, is the long lead inflow platinum resistance thermometer sensor, of r1 through resistance, and the electric current among r1 and the Rt is I (200 μ A); Behind the 200 μ A electric current mistakes-V end that flows out by constant current source-I, be that the long lead of r2 converges with+electric current that I flows out in the lower end of platinum resistance thermometer sensor, through resistance, be prone to know according to Kirchhoff's current law (KCL), the electric current that flows through conductor resistance r3 for+I with-I sum, i.e. 400 μ A.
According to r1=r2=r3=r4=r, get following equality:
+V?=?I*（r1+Rt）+2I*r3?=?I*?Rt+3I*r；
-V?=?I*?r2+2I*?r3?=?3I*r；
More than two formulas subtract each other, the voltage difference that can get the positive and negative input end of instrument amplifier U3 is U=I* Rt, this is the voltage at platinum resistance thermometer sensor, two ends; Measure this voltage by single-chip microcomputer; Because I is known, can obtain the resistance Rt of current platinum resistance thermometer sensor,, bring the value of Rt into formula: Rt=R0* (1+A*t+B*t
2), get final product temperature t.In the following formula, the resistance value of platinum resistance thermometer sensor, when R0 is 0 ℃; The resistance value of platinum resistance thermometer sensor, when Rt is t ℃.Constant A, B in the formula are respectively: A=3.908 02 * 10
– 3, B=-5.801 95 * 10
– 7, for the thermal resistance of different model or material, the numerical value of these two parameters is different.
In the 4 line system thermometrics of Fig. 7, only used a constant current source+I, lead r3 and r4 directly receive two input ends of instrument amplifier U3; Because the input impedance of instrument amplifier U3 is very big; Therefore to go up electric current with r4 be 0 to lead r3, can know that by Fig. 7 the electric current I that constant current source+I flows out flows into Rt through r1, flows back to simulation ground through r2 again; The voltage at instrument amplifier U3 two ends is: U=I*Rt, this is the platinum resistance thermometer sensor, voltage.Though it is different to this shows that 3 line systems and 4 line systems connect method, the voltage relationship formula of actual input amplifier is the same, and therefore the data processing method of 4 line systems is with above-mentioned 3 line system disposal routes.
Be illustrated in figure 4 as the data processing of the utility model and the circuit theory diagrams of communication interface circuit; Wherein, data processing circuit 3 is made up of voltage amplifier circuit 3-1, analogue filter circuit 3-2, analog to digital conversion circuit 3-3 and single chip machine controlling circuit 3-4.
Among Fig. 4, the band that voltage amplifier circuit 3-1 is made up of instrument amplifier U3, resistance R 10, R11 and capacitor C 5-C7 suppresses the voltage amplifier circuit of Radio frequency interference (RFI); Voltage+V that thermal resistance Rt two ends produce ,-V connects 3 pin of input end in the same way, reverse input end 2 pin of instrument amplifier U3 respectively through resistance R 10, R11; Capacitor C 6 is connected between 3 pin of input end in the same way and ground of instrument amplifier U3; Capacitor C 7 is connected between reverse input end 2 pin and ground of instrument amplifier U3, and capacitor C 5 is connected between 3 pin of input end in the same way and reverse input end 2 pin of instrument amplifier U3; Gain resistor end 1 pin of instrument amplifier U3 and 8 pin also connect, and power end 7 pin of instrument amplifier U3,4 pin connect respectively+9V voltage ,-9V voltage.
The utility model is used for measuring 0-400 ℃ temperature; Divide kilsyth basalt can know about 250 Ω of its corresponding resistance 400 degrees centigrade the time by Pt100; Adopt the steady current of 200 μ A to flow through Pt100; The upper voltage limit that can know thermal resistance Pt100 two ends is 250 Ω *, 200 μ A=50mV approximately, amplifies 100 times and can obtain 5V output.Instrument amplifier U3 adopts the AD621 instrument to amplify chip, is a use, low cost, low-power consumption, the high-precision meter amplifier of being easy to, and is fit to numerous applications.It melts high-performance, small size and low-power consumption in one, is superior to the design of discrete amplifier.Utilize internal gain that resistance is set, can realize high-effect, low gain sum of errors low gain drift error.Then fixed gain 10 and 100 can be set through the external pin overlap joint; The utility model adopts the integrated instrument amplifier of AD621 to realize the precision amplification and the differential-to-single-ended conversion of signal, the problem of instrument amplifier difficult parameters to mate of having avoided many amplifiers to constitute simultaneously; With 1 and 8 pin short circuits, can realize amplifying 100 times; The AD621 power supply voltage range is wide in addition, can be practical in ± 2.3V-± 18V scope, and the utility model adopts illustrated positive and negative 9V dual power supply.
Among Fig. 4, analogue filter circuit 3-2 is the fertile low-pass filter of being made up of operational amplifier U4, resistance R 12, R13, capacitor C 1, C2 now of the active Bart in 2 rank; Output terminal 6 pin of instrument amplifier U3 connect 3 pin of input end in the same way of operational amplifier U4 successively through resistance R 12, R13; Reverse input end 2 pin of operational amplifier U4 connect its output terminal 6 pin; The output terminal 6 foot meridian capacitor C1 connecting resistance R12 of operational amplifier U4 and the node of resistance R 13; Power end 7 pin of operational amplifier U4,4 pin connect respectively+9V voltage ,-9V voltage, capacitor C 2 is connected between 3 pin of input end in the same way and ground of operational amplifier U4.
Signal demand after front end instrument amplifier AD621 amplifies is sent into wave filter and is carried out anti-aliasing filter.The active low-pass filter that the utility model adopts OP07 to constitute carries out anti-aliasing filter, suppresses high frequency noise simultaneously.The OP07 chip is a kind of low noise, and the bipolarity operational amplifier integrated circuit of non-chopper-zero-stabilized is because it has low-down input offset voltage, so OP07 does not need extra zeroing measure in the plurality of applications occasion.OP07 have simultaneously input bias current low (OP07A for ± 2nA) with the characteristics of open-loop gain high (is 300V/mV for OP07A), the characteristic of this low imbalance, high open-loop gain makes OP07 be specially adapted to the aspects such as feeble signal of the measuring equipment and the amplification sensor of high-gain.
Butterworth filter is the very smooth wave filter of a kind of amplitude response, and equal ripple-free can keep the accurate signal level in passband and the stopband, is suitable for doing very much the frequency overlapped-resistable filter in the data-switching.The utility model uses the fertile low-pass filter now of the active Bart in 2 rank, and it adopts the Sallen-Key topological structure, and Butterworth response can be provided; The Sallen-Key topological structure is also referred to as VCVS (VCVS) structure; Its simplicity of design, circuit component is few, in the industry cycle widely uses.
Among Fig. 4, analog to digital conversion circuit 3-3 is made up of analog to digital converter U5, reference voltage source U2, resistance R 3 and potentiometer R4; Output terminal 6 pin of operational amplifier U4 connect input end 2 pin of analog to digital converter U5, and power end 8 pin of analog to digital converter U5 connect simulation+5VA voltage; 3 pin of analog to digital converter U5 and 4 pin also connect back ground connection; 3 pin of reference voltage source U2,4 pin connect respectively voltage+Vcc; Resistance R 3 is connected between 1 pin of voltage+Vcc and reference voltage source U2; Potentiometer R4 is connected between 1 pin and ground of reference voltage source U2; The 2 pin ground connection of reference voltage source U2, the swing arm of potentiometer R4 connect reference voltage end 1 pin of analog to digital converter U5.
The Pt100 platinum resistance thermometer sensor, in 0-400 ℃ of scope, 1 ℃ of the every variation of temperature, on average about 0.37 Ω of its change in resistance, therefore, the steady current that flows through 200 μ A can produce voltage 0.074mV, the voltage after amplifying 100 times is 7.4mV.The utility model adopts 12 A/D conversion chip ADS1286, and when adopting the 5V voltage reference, resolution is 5V/4096=1.22mV, and minimum can be told 1.22/7.4=0.165 ℃ temperature variation.If the resolution requirement to temperature in the practical application is not high, can adopt with 10 compatible fully A/D conversion chips of its pin and realize TLC1549 replacement or 8 A/D conversion chip TLC549 replacements, and circuit need not be done any change.
Realize accurate measurement; The reference voltage end of analog to digital converter U5 must be selected high-precision reference voltage source for use; The utility model adopts accurate reference voltage chip LM399 to obtain the A/D changing voltage benchmark of 5V; Because the novel voltage stabilizing pipe that LM399 inside has adopted the buried technology of subsurface to make has extremely low voltage temperature coefficient, is low to moderate 0.3 * 10
-6/ ℃, only be equivalent to 1/10th of general reference voltage source, also be that other reference voltage source is unapproachable.
Among Fig. 4, single chip machine controlling circuit 3-4 is made up of single-chip microcomputer U1, power isolation module U15, crystal oscillator Y1, capacitor C 3, C4, C8 and resistance R 17; Input end 2 pin of power isolation module U15 connect+5V voltage, and 1 pin of power isolation module U15,3 pin, 4 pin are respectively DGND, V485, GND485; Crystal oscillator Y1 is connected between 4,5 pin of single-chip microcomputer U1; Capacitor C 3 is connected between 4 pin and DGND of single-chip microcomputer U1; Capacitor C 4 is connected between 5 pin and DGND of single-chip microcomputer U1, and resistance R 17 is connected between 1 pin and DGND of single-chip microcomputer U1, and the 1 foot meridian capacitor C8 of single-chip microcomputer U1 connects+5V voltage; The 5-7 pin of said analog to digital converter U5 connects the 12-14 pin of single-chip microcomputer U1 respectively.
The utility model adopts the control core of the superpower anti-interference series monolithic STC11F04E of high speed as device, realizes data acquisition and data transmission.It has the EEPROM of 1KB, can realize the memory storage function of module parameter, can read the parameter that be provided with last time after promptly module powers on, and by this parameter work; And the standard of employing MODBUS communication protocol can directly be communicated by letter with the industrial configuration software of host computer.SCM program has comprised that thermal resistance voltage acquisition program, digital filter program, data processor, MODBUS signal procedure, EEPROM read and write control program; Can communicate through the RS485 interface according to MODBUS agreement and host computer watchdog routine; And the temperature data uploading after will handling, can also realize modification through the host computer testing software simultaneously to the module communication parameter.The utility model can write that watchdog routine is communicated by letter with LabVIEW, VB, VC or configuration software and direct displays temperature.
Among Fig. 4, communication interface circuit 4 is made up of 485 communication interface chip U14, first to the 3rd photoelectrical coupler U11-U13, TVS pipe D5-D7, resistance R 7-R9, R14-R16, R19-R23 and interface J1; 7 pin of single-chip microcomputer U1,3 pin connect input end 2 pin of the first photoelectrical coupler U11, the 3rd photoelectrical coupler U13 respectively; Input end 1 pin of the first photoelectrical coupler U11, the 3rd photoelectrical coupler U13 connects+5V voltage through resistance R 7, resistance R 9 respectively; 3 pin of first to the 3rd photoelectrical coupler U11-U13 are ground connection respectively; Output terminal 4 pin of the first photoelectrical coupler U11, the 3rd photoelectrical coupler U13 connect 2 pin, 4 pin of 485 communication interface chip U14 respectively; Resistance R 20 is connected between output terminal 4 pin and V485 of the first photoelectrical coupler U11, and resistance R 21 is connected between output terminal 4 pin and V485 of the 3rd photoelectrical coupler U13; 1 pin of said 485 communication interface chip U14 connects input end 2 pin of the second photoelectrical coupler U12; Input end 1 pin of the second photoelectrical coupler U12 meets V485 through resistance R 8; Output terminal 4 pin of the second photoelectrical coupler U12 connect 2 pin of single-chip microcomputer U1, resistance R 19 be connected on the second photoelectrical coupler U12 output terminal 4 pin and+5V voltage between; 3 pin of 485 communication interface chip U14 and 2 pin also connect; 8 pin, 5 pin of 485 communication interface chip U14 connect respectively+5V voltage; 6,7 pin of 485 communication interface chip U14 are output as signal end DATA+, DATA-respectively after resistance R 23, resistance R 22; Signal end DATA+, DATA-meet GND485 through TVS pipe D7, TVS pipe D5 respectively, and TVS pipe D6 is connected between signal end DATA+ and the DATA-; 1,2 pin of interface J1 meet signal end DATA+, DATA-respectively; Resistance R 14 is connected between 7 pin and GND485 of 485 communication interface chip U14, and resistance R 16 is connected between 6 pin and V485 of 485 communication interface chip U9, and resistance R 15 is connected between 6 pin and 7 pin of 485 communication interface chip U14.
The DC-DC insulating power supply module B0505S of the utility model employing 1W realizes the isolation of optocoupler two ends power supply in the 485 chip light isolated communication circuit, its input voltage 5V, output voltage 5V; The standard serial mouth RXD of single-chip microcomputer and TXD are connected to the RO pin and the DI pin of MAX485 chip respectively through photoelectrical coupler TLP521-1.
Transmission/receptions by the D/R signal controlling MAX485 chip of single-chip microcomputer output enables: the D/R signal is " 1 ", and then the transmitter of MAX485 chip is effective, and receiver forbids that this moment, single-chip microcomputer can be to RS-485 bus transmission data; The D/R signal is " 0 ", and then the transmitter of MAX485 chip is forbidden, receiver is effective, and this moment, single-chip microcomputer can receive the data from the RS-485 bus.In this circuit, " receiver " and " transmitter " in arbitrary moment MAX485 chip be merely able to have 1 in running order.
Be connected to the pull-up resistor R16 of A pin, the pull down resistor R14 that is connected to the B pin is used to guarantee that connectionless MAX485 chip is in idle condition; The network failure protection is provided; Can make the A terminal potential be higher than the B end like this; The RXD end presents constant high level, and it is chaotic to prevent that single-chip microcomputer from receiving, to improve the reliability of RS-485 node and network.R15 is the terminal build-out resistor, chooses according to actual needs.
In order to protect the RS-485 network more reliably, guarantee security of system, increase some holding circuits.Clamper all is used for protecting the RS-485 bus in the TVS of 6.8V pipe D5-D7 among Fig. 4, avoids the RS-485 bus high pressure that (like thunderbolt, surge etc.) produce when receiving external interference to damage the RS-485 transceiver; Resistance R 22 among Fig. 4 can make the hardware fault of this machine that communicating by letter of whole bus is affected with R23.
The utility model employing platinum resistance thermometer sensor, Pt100 is used for the measurement of scene temperature, temperature-measuring range 0-400 ℃.Adopt identical data processing circuit,, can realize the platinum resistor temperature measuring of 2,3,4 line systems according to practical situations without any need for the extra setting of software and hardware.Wherein, the mode of connection of 2 lines is used for temperature survey is required lower occasion, and external thermal resistance and temperature measurement circuit distance is unsuitable long, otherwise error can be excessive, and 3 lines and 4 line systems can realize the measurement of degree of precision; The default communication parameter was when the utility model used first: baud rate 9600bps, address number 1; Can use the software modification above-mentioned parameter that carries.
Claims (9)
1. thermal resistance temperature measuring equipment; It is characterized in that: comprise thermal resistance (Rt), power circuit (1), constant-current source circuit (2) and data processing circuit (3) and the communication interface circuit (4) formed by voltage amplifier circuit (3-1), analogue filter circuit (3-2), analog to digital conversion circuit (3-3), single chip machine controlling circuit (3-4); The output terminal of said power circuit (1) connects the corresponding power end of other circuit modules respectively; The current input terminal of the output termination thermal resistance (Rt) of said constant-current source circuit (2); The voltage signal of thermal resistance (Rt) two ends output is connected on two input ends of voltage amplifier circuit (3-1); The output terminal of voltage amplifier circuit (3-1) connects the input end of single chip machine controlling circuit (3-4), single chip machine controlling circuit (3-4) and two-way connection of communication interface circuit (4) successively through analogue filter circuit (3-2), analog to digital conversion circuit (3-3).
2. a kind of thermal resistance temperature measuring equipment according to claim 1 is characterized in that: said thermal resistance (Rt) is the Pt100 platinum resistance thermometer sensor.
3. a kind of thermal resistance temperature measuring equipment according to claim 1 is characterized in that: said power circuit (1) is made up of first voltage stabilizer (U8), voltage reversal device (U10), second voltage stabilizer (U9), protection diode D3, D4, light emitting diode D8, magnetic bead (L1), capacitor C 9-C12 and resistance R 18; Positive pole+the Vs of external direct current power supply is voltage+Vcc behind protection diode D3; Voltage+Vcc connects input end 1 pin of first voltage stabilizer (U8) and second voltage stabilizer (U9) respectively, and 2 pin of second voltage stabilizer (U9) connect the negative pole of external direct current power supply through protection diode D4; Output terminal 3 pin of first voltage stabilizer (U8) are+9V voltage that capacitor C 9 is connected between output terminal 3 pin and ground of first voltage stabilizer (U8); Input end 8 pin of voltage reversal device (U10) connect output terminal 3 pin of first voltage stabilizer (U8); Output terminal 5 pin of voltage reversal device (U10) are-9V voltage; Capacitor C 12 is connected between output terminal 5 pin and ground of voltage reversal device (U10), and capacitor C 11 is connected between 2 pin and 4 pin of voltage reversal device (U10); Output terminal 3 pin of second voltage stabilizer (U9) are+5V voltage; Capacitor C 10 is connected between output terminal 3 pin and ground of second voltage stabilizer (U9); Output terminal 3 pin of second voltage stabilizer (U9) are output as simulation+5VA voltage behind magnetic bead (L1), resistance R 18 be connected between simulation+5VA voltage and the ground after light emitting diode D8 connects.
4. a kind of thermal resistance temperature measuring equipment according to claim 3; It is characterized in that: the constant current source with temperature compensation of said constant-current source circuit (2) for being made up of two the three adjustable constant current sources of end (U6, U7), resistance R 1, R2, R5, R6 and diode D1, D2, the steady current of its output be respectively+I ,-I.
5. a kind of thermal resistance temperature measuring equipment according to claim 3 is characterized in that: the band that said voltage amplifier circuit (3-1) is made up of instrument amplifier (U3), resistance R 10, R11 and capacitor C 5-C7 suppresses the voltage amplifier circuit of Radio frequency interference (RFI); Voltage+V that thermal resistance (Rt) two ends produce ,-V connects 3 pin of input end in the same way, reverse input end 2 pin of instrument amplifier (U3) respectively through resistance R 10, R11; Capacitor C 6 is connected between 3 pin of input end in the same way and ground of instrument amplifier (U3); Capacitor C 7 is connected between reverse input end 2 pin and ground of instrument amplifier (U3), and capacitor C 5 is connected between 3 pin of input end in the same way and reverse input end 2 pin of instrument amplifier (U3); Gain resistor end 1 pin of instrument amplifier (U3) and 8 pin also connect, and power end 7 pin of instrument amplifier (U3), 4 pin connect respectively+9V voltage ,-9V voltage.
6. a kind of thermal resistance temperature measuring equipment according to claim 5 is characterized in that: said analogue filter circuit (3-2) is the fertile low-pass filter now of the active Bart in 2 rank who is made up of operational amplifier (U4), resistance R 12, R13, capacitor C 1, C2; Output terminal 6 pin of said instrument amplifier (U3) connect 3 pin of input end in the same way of operational amplifier (U4) successively through resistance R 12, R13; Reverse input end 2 pin of operational amplifier (U4) connect its output terminal 6 pin; The output terminal 6 foot meridian capacitor C1 connecting resistance R12 of operational amplifier (U4) and the node of resistance R 13; Power end 7 pin of operational amplifier (U4), 4 pin connect respectively+9V voltage ,-9V voltage, capacitor C 2 is connected between 3 pin of input end in the same way and ground of operational amplifier (U4).
7. a kind of thermal resistance temperature measuring equipment according to claim 6 is characterized in that: analog-digital conversion circuit as described (3-3) is made up of analog to digital converter (U5), reference voltage source (U2), resistance R 3 and potentiometer (R4); Output terminal 6 pin of said operational amplifier (U4) connect input end 2 pin of analog to digital converter (U5), and power end 8 pin of analog to digital converter (U5) connect simulation+5VA voltage; 3 pin of analog to digital converter (U5) and 4 pin also connect back ground connection; 3 pin of reference voltage source (U2), 4 pin connect respectively voltage+Vcc; Resistance R 3 is connected between 1 pin of voltage+Vcc and reference voltage source (U2); Potentiometer (R4) is connected between 1 pin and ground of reference voltage source (U2); 2 pin ground connection of reference voltage source (U2), the swing arm of potentiometer (R4) connect reference voltage end 1 pin of analog to digital converter (U5).
8. a kind of thermal resistance temperature measuring equipment according to claim 7 is characterized in that: said single chip machine controlling circuit (3-4) is made up of single-chip microcomputer (U1), power isolation module (U15), crystal oscillator (Y1), capacitor C 3, C4, C8 and resistance R 17; Input end 2 pin of said power isolation module (U15) connect+5V voltage, and 1 pin of power isolation module (U15), 3 pin, 4 pin are respectively DGND, V485, GND485; Crystal oscillator (Y1) is connected between 4,5 pin of single-chip microcomputer (U1); Capacitor C 3 is connected between 4 pin and DGND of single-chip microcomputer (U1); Capacitor C 4 is connected between 5 pin and DGND of single-chip microcomputer (U1); Resistance R 17 is connected between 1 pin and DGND of single-chip microcomputer (U1), and 1 foot meridian capacitor C8 of single-chip microcomputer (U1) connects+5V voltage; The 5-7 pin of said analog to digital converter (U5) connects the 12-14 pin of single-chip microcomputer (U1) respectively.
9. a kind of thermal resistance temperature measuring equipment according to claim 8 is characterized in that: said communication interface circuit (4) is made up of 485 communication interface chips (U14), first to the 3rd photoelectrical coupler (U11-U13), TVS pipe D5-D7, resistance R 7-R9, R14-R16, R19-R23 and interface (J1); 7 pin of said single-chip microcomputer (U1), 3 pin connect input end 2 pin of first photoelectrical coupler (U11), the 3rd photoelectrical coupler (U13) respectively; Input end 1 pin of first photoelectrical coupler (U11), the 3rd photoelectrical coupler (U13) connects+5V voltage through resistance R 7, resistance R 9 respectively; 3 pin of first to the 3rd photoelectrical coupler (U11-U13) are ground connection respectively; Output terminal 4 pin of first photoelectrical coupler (U11), the 3rd photoelectrical coupler (U13) connect 2 pin, 4 pin of 485 communication interface chips (U14) respectively; Resistance R 20 is connected between output terminal 4 pin and V485 of first photoelectrical coupler (U11), and resistance R 21 is connected between output terminal 4 pin and V485 of the 3rd photoelectrical coupler (U13); 1 pin of said 485 communication interface chips (U14) connects input end 2 pin of second photoelectrical coupler (U12); Input end 1 pin of second photoelectrical coupler (U12) meets V485 through resistance R 8; Output terminal 4 pin of second photoelectrical coupler (U12) connect 2 pin of single-chip microcomputer (U1), resistance R 19 be connected on second photoelectrical coupler (U12) output terminal 4 pin and+5V voltage between; 3 pin of 485 communication interface chips (U14) and 2 pin also connect; 8 pin, 5 pin of 485 communication interface chips (U14) connect respectively+5V voltage; 6,7 pin of 485 communication interface chips (U14) are output as signal end DATA+, DATA-respectively after resistance R 23, resistance R 22; Signal end DATA+, DATA-meet GND485 through TVS pipe D7, TVS pipe D5 respectively, and TVS pipe D6 is connected between signal end DATA+ and the DATA-; 1,2 pin of interface (J1) meet signal end DATA+, DATA-respectively; Resistance R 14 is connected between 7 pin and GND485 of 485 communication interface chips (U14), and resistance R 16 is connected between 6 pin and V485 of 485 communication interface chips (U9), and resistance R 15 is connected between 6 pin and 7 pin of 485 communication interface chips (U14).
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| CN2012200251415U CN202442810U (en) | 2012-01-19 | 2012-01-19 | Thermal resistor temperature measuring device |
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