CN219641115U

CN219641115U - Sampling device and temperature measuring device that temperature resistant floats

Info

Publication number: CN219641115U
Application number: CN202321664227.7U
Authority: CN
Inventors: 何子峰; 郝磊; 王建栋; 王振华; 杨建辉; 魏学乐; 唐亮; 耿晓娅
Original assignee: Dongfang Green Energy Hebei Co ltd Shijiazhuang Thermal Branch
Current assignee: Dongfang Green Energy Hebei Co ltd Shijiazhuang Thermal Branch
Priority date: 2023-06-28
Filing date: 2023-06-28
Publication date: 2023-09-05
Anticipated expiration: 2033-06-28

Abstract

The utility model discloses a temperature drift resistant sampling device and a temperature measuring device, and relates to the technical field of temperature measuring devices; the sampling device comprises a constant-current reference voltage circuit, a first operational amplifier unit U1A, a second operational amplifier unit U1B, a third operational amplifier unit U1C, an analog switch U2, a first temperature sensor, a second temperature sensor, a first reference resistor, a second reference resistor, an amplifying circuit and an amplifying reference circuit, wherein the constant-current reference voltage circuit is connected with the analog switch U2 through the first operational amplifier unit U1A, and the constant-current reference voltage circuit is connected with the gating end of the analog switch U2 through the second reference resistor and the first reference resistor in sequence, and the gating end of the analog switch U2 is connected with the junction of the second reference resistor and the first reference resistor; the temperature measuring device comprises the sampling device and the controller U3, and the temperature drift of the sampling device is reduced through the two reference resistors, the operational amplifier unit and the like, so that the obtained sampling data are more accurate, and the temperature measuring data obtained by the controller are more accurate.

Description

Sampling device and temperature measuring device that temperature resistant floats

Technical Field

The utility model relates to the technical field of temperature measuring devices, in particular to a temperature drift resistant sampling device and a temperature measuring device.

Background

The authorized bulletin number is CN211824797U, and the name is a temperature measuring circuit. Hereinafter, reference 1 is abbreviated. Comprising the following steps: the output end of the constant current source circuit and the output end of the control circuit are respectively connected with the input end of the analog switch selection circuit, the input end of the amplifying circuit is connected with the output end of the analog switch selection circuit, the output end of the amplifying circuit is connected with the input end of the control circuit through the AD converter, and the output end of the power circuit is respectively connected with the analog switch selection circuit, the constant current source circuit, the amplifying circuit and the control circuit. The temperature measuring circuit can improve the temperature measuring accuracy.

The authorized bulletin number is CN110987223B, and the name is an improved high-precision platinum resistance temperature measuring circuit. Hereinafter, reference 2 is abbreviated. The temperature measuring circuit comprises an excitation source UEX, a platinum resistor Rt, a reference resistor RREF, a standard resistor RSTD, a first signal operational amplifier part and a second signal operational amplifier part, wherein the excitation source UEX, the platinum resistor Rt, the reference resistor RREF and the standard resistor RSTD are connected in series, the excitation source UEX is a 5V excitation source, the first signal operational amplifier part is connected to two ends of the platinum resistor Rt and the reference resistor RREF and is used for outputting amplification gain Uout of voltage drop difference of the platinum resistor Rt and the reference resistor RREF, the second signal operational amplifier part is connected to two ends of the standard resistor RSTD and is used for outputting voltage drop Us of the standard resistor RSTD, and a temperature measuring circuit uses a 12-bit AD module to acquire and output, so that the accuracy of 0.01 ℃ can be achieved.

The authorized bulletin number is CN210322060U, and the name is a thermocouple measurement module based on a field bus. Hereinafter, reference 3 is abbreviated. The device comprises a processor, an Ethernet switch, a power module and a bus isolation unit, wherein the processor is respectively electrically connected with the Ethernet switch, the power module and the bus isolation unit, one path of the Ethernet switch is electrically connected with an Ethernet connector LINK1 after passing through an isolation transformer, the other path of the Ethernet switch is electrically connected with an Ethernet connector LINK2 after passing through the isolation transformer, the bus isolation unit is electrically connected with a plurality of paths of analog switches through an analog-to-digital converter, and the plurality of paths of analog switches are electrically connected with an IO interface connector after sequentially passing through a low-pass filter circuit and an overvoltage protection circuit. All measuring ports of the module can be used for measuring thermal resistance RTD and thermocouple TC, can be configured randomly, integrates standard Ethernet industrial protocols, is particularly suitable for large-data-volume transmission and real-time control of temperature measuring systems, facilitates rapid networking and system expansion in industrial sites, and meets different requirements of customers.

The platinum resistance temperature sensor is used as a high-precision temperature sensor and is widely applied to the fields of weather, automobiles, aviation, industrial automatic measurement, various experimental instruments and the like. The temperature measurement principle of the platinum resistance temperature sensor is that the resistance value of the platinum PT changes along with the environmental temperature, and a certain functional relation exists between the resistance value and the temperature value.

Because the singlechip can not directly measure the resistance value of the platinum resistor, a temperature measurement conversion circuit is required to be designed to convert the resistance value signal of the platinum resistor into a signal which can be identified by the singlechip.

The inventor believes that the traditional temperature measuring circuit cannot meet the temperature measuring requirement due to the problems of poor temperature measuring precision, high cost, incapability of resisting temperature drift and the like.

Problems and considerations in the prior art:

how to solve the technical problem of larger temperature drift of the sampling device.

Disclosure of Invention

The utility model provides a sampling device and a temperature measuring device for resisting temperature drift, which solve the technical problem that the sampling device is large in temperature drift.

In order to solve the technical problems, the technical scheme adopted by the utility model is as follows:

the temperature drift resistance sampling device comprises a constant current reference voltage circuit, an analog switch U2, a first temperature sensor, a second temperature sensor, a temperature reference circuit, an amplifying circuit and an amplifying reference circuit, wherein the first temperature sensor is connected between the constant current reference voltage circuit and the gating end of the analog switch U2, the second temperature sensor is connected between the constant current reference voltage circuit and the gating end of the analog switch U2, the temperature reference circuit comprises a first reference resistor and a second reference resistor, the operational amplifier U1 comprises a first operational amplifier unit U1A, a second operational amplifier unit U1B and a third operational amplifier unit U1C, the amplifying circuit comprises a second operational amplifier unit U1B, the constant current reference voltage circuit is connected with the analog switch U2 through the first operational amplifier unit U1A, the constant current reference voltage circuit is sequentially connected with the gating end of the analog switch U2 through the second reference resistor and the first reference resistor, the gating end of the analog switch U2 is connected with the second reference resistor, the operational amplifier U1 is connected with the junction of the first reference resistor, and the output end of the analog switch U2 is connected with the second operational amplifier unit U1B through the second operational amplifier unit U1B.

The further technical proposal is that: the constant current reference voltage circuit and the first operational amplifier unit U1A form a constant current source circuit, the first reference resistor is used for providing a voltage parameter at a first temperature, the second reference resistor is used for providing a voltage parameter at a second temperature, the switch selection end of the analog switch U2 is used for being connected with a controller, and the output end of the second operational amplifier unit U1B is used for being connected with the controller.

The further technical proposal is that: the constant-current reference voltage circuit comprises a first resistor R1, a second resistor R2 and a sixth resistor R6, wherein the first input end of the first operational amplifier unit U1A is connected with VCC through the first resistor R1, the first input end of the first operational amplifier unit U1A is grounded through the second resistor R2, the second input end of the first operational amplifier unit U1A is grounded through the sixth resistor R6, the gating end of the analog switch U2 is sequentially grounded through a first temperature sensor and the sixth resistor R6 and forms a first gating branch, the gating end of the analog switch U2 is sequentially grounded through the second temperature sensor and the sixth resistor R6 and forms a second gating branch, the gating end of the analog switch U2 is sequentially grounded through the first reference resistor, the second reference resistor and the sixth resistor R6 and forms a third gating branch, and the gating end of the analog switch U2 is sequentially grounded through the second reference resistor and the sixth resistor R6 and forms a fourth gating branch.

The further technical proposal is that: the amplifying reference circuit comprises a ninth resistor R9 and a tenth resistor R10, the first input end of the third operational amplifier unit U1C is connected with VCC through the ninth resistor R9, the first input end of the third operational amplifier unit U1C is grounded through the tenth resistor R10, and the second input end of the third operational amplifier unit U1C is connected with the output end of the third operational amplifier unit U1C.

The further technical proposal is that: the amplifying circuit further comprises a seventh resistor R7 and an eighth resistor R8, the output end ZA of the analog switch U2 is connected with the first input end of the second operational amplifier unit U1B, the output end of the third operational amplifier unit U1C is connected with the second input end of the second operational amplifier unit U1B through the eighth resistor R8, and the seventh resistor R7 is connected between the second input end of the second operational amplifier unit U1B and the output end of the second operational amplifier unit U1B.

The temperature measuring device resistant to temperature drift comprises the sampling device, a controller U3, a switch selection end of an analog switch U2, and an output end of a second operational amplifier unit U1B.

The further technical proposal is that: the switch selection end of the analog switch U2 comprises a first switch selection end and a second switch selection end, the first switch selection end of the analog switch U2 is connected with the control end of the controller, and the second switch selection end of the analog switch U2 is connected with the control end of the controller.

The further technical proposal is that: the output end of the second operational amplifier unit U1B is connected with the controller through the fourth resistor R4.

The beneficial effects of adopting above-mentioned technical scheme to produce lie in:

first, a sampling device of temperature drift resistance includes constant current reference voltage circuit, analog switch U2, first temperature sensor, second temperature sensor, temperature reference circuit, amplifier circuit and amplifier reference circuit, and first temperature sensor connects between constant current reference voltage circuit and analog switch U2's gate end, and the second temperature sensor connects between constant current reference voltage circuit and analog switch U2's gate end, still includes operational amplifier U1, temperature reference circuit includes first reference resistor and second reference resistor, operational amplifier U1 includes first operational amplifier unit U1A, second operational amplifier unit U1B and third operational amplifier unit U1C, amplifier circuit includes second operational amplifier unit U1B, and constant current reference voltage circuit connects with analog switch U2 through first operational amplifier unit U1A, and constant current reference voltage circuit connects analog switch U2's gate end through second reference resistor and first reference resistor in proper order, and the junction of analog switch U2's termination second reference resistor and first reference resistor, the output unit of second operational amplifier unit U1B connects with the second operational amplifier unit U1C through second operational amplifier unit U1B. According to the technical scheme, the temperature drift of the sampling device is reduced through the two reference resistors, the operational amplifier and the like, and the obtained sampling data are more accurate.

Second, a temperature measuring device of anti temperature drift includes above-mentioned sampling device, still includes controller U3, and analog switch U2's switch select end is connected with the controller, and the output of second operational amplifier unit U1B is connected with the controller. According to the technical scheme, the temperature drift of the sampling device is reduced through the two reference resistors, the operational amplifier and the like, the obtained sampling data are more accurate, and then the temperature measurement data obtained by the controller are more accurate.

See the description of the detailed description section.

Drawings

FIG. 1 is a schematic block diagram of embodiment 1 of the present utility model;

fig. 2 is a schematic circuit diagram of embodiment 1 of the present utility model.

Detailed Description

The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the utility model, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present utility model, but the present utility model may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present utility model is not limited to the specific embodiments disclosed below.

Example 1:

as shown in fig. 1 and 2, the utility model discloses a temperature measuring device capable of resisting temperature drift, which comprises a constant-current reference voltage circuit, an operational amplifier U1, an analog switch U2, a controller U3, a first temperature sensor, a second temperature sensor, a temperature reference circuit, an amplifying reference circuit and a fourth resistor R4, wherein the temperature reference circuit comprises a first reference resistor and a second reference resistor, and the operational amplifier U1 comprises a first operational amplifier unit U1A, a second operational amplifier unit U1B and a third operational amplifier unit U1C.

As shown in fig. 1, the constant current reference voltage circuit is connected to the analog switch U2 through the first operational amplifier unit U1A, the constant current reference voltage circuit includes a first resistor R1, a second resistor R2 and a sixth resistor R6, the first input end of the first operational amplifier unit U1A is connected to VCC through the first resistor R1, VCC is +3.3v, the first input end of the first operational amplifier unit U1A is grounded through the second resistor R2, the second input end of the first operational amplifier unit U1A is grounded through the sixth resistor R6, and the constant current reference voltage circuit and the first operational amplifier unit U1A form a constant current source circuit.

As shown in fig. 1, a first temperature sensor, namely a first platinum resistor PT1, and a second temperature sensor, namely a second platinum resistor PT2, are connected between a constant current reference voltage circuit and a gating end of an analog switch U2, the second temperature sensor is connected between the constant current reference voltage circuit and the gating end of the analog switch U2, the gating end of the analog switch U2 is grounded through the first temperature sensor and a sixth resistor R6 in sequence and forms a first gating branch, and the gating end of the analog switch U2 is grounded through the second temperature sensor and the sixth resistor R6 in sequence and forms a second gating branch.

As shown in fig. 1, the first reference resistor is used for providing a voltage parameter at the first temperature, the second reference resistor is used for providing a voltage parameter at the second temperature, the first reference resistor is a third resistor R3, the second reference resistor is a fifth resistor R5, the constant current reference voltage circuit is sequentially connected with the gating end of the analog switch U2 through the second reference resistor and the first reference resistor, the gating end of the analog switch U2 is connected with the junction of the second reference resistor and the first reference resistor, the gating end of the analog switch U2 is sequentially grounded through the first reference resistor, the second reference resistor and the sixth resistor R6 and forms a third gating branch, and the gating end of the analog switch U2 is sequentially grounded through the second reference resistor and the sixth resistor R6 and forms a fourth gating branch.

As shown in fig. 1, the amplifying reference circuit includes a ninth resistor R9 and a tenth resistor R10, the first input end of the third operational amplifier unit U1C is connected to VCC through the ninth resistor R9, the first input end of the third operational amplifier unit U1C is grounded through the tenth resistor R10, and the second input end of the third operational amplifier unit U1C is connected to the output end of the third operational amplifier unit U1C.

As shown in fig. 1, the amplifying circuit includes a second operational amplifier unit U1B, a seventh resistor R7, and an eighth resistor R8, where an output end of the analog switch U2 is connected to an input end of the second operational amplifier unit U1B, an amplifying reference circuit is connected to a second input end of the second operational amplifier unit U1B through a third operational amplifier unit U1C, an output end ZA of the analog switch U2 is connected to a first input end of the second operational amplifier unit U1B, an output end of the third operational amplifier unit U1C is connected to a second input end of the second operational amplifier unit U1B through the eighth resistor R8, and the seventh resistor R7 is connected between the second input end of the second operational amplifier unit U1B and an output end of the second operational amplifier unit U1B.

As shown in fig. 1, a switch selection end of the analog switch U2 is connected to the controller U3, and an output end of the second op-amp unit U1B is connected to the controller U3. The switch selection end of the analog switch U2 comprises a first switch selection end and a second switch selection end, the first switch selection end of the analog switch U2 is connected with the control end of the controller U3, and the second switch selection end of the analog switch U2 is connected with the control end of the controller U3. The output end of the second operational amplifier unit U1B is connected with the controller U3 through a fourth resistor R4.

As shown in FIG. 1, the controller U3 is a single-chip microcomputer, and the model of the controller U3 is stc8H8K64U.

As shown in fig. 2, the model of the operational amplifier U1 is LMV324, the model of the analog switch U2 is 74HC4052, the operational amplifier, the analog switch, the controller and the corresponding connection technology are not described in detail herein, and the auxiliary devices such as the capacitor and the corresponding connection technology are not described in detail herein. The technical scheme of the utility model does not relate to the improvement of the algorithm.

Example 2:

the utility model discloses a temperature drift resistant sampling device which comprises a constant current reference voltage circuit, an operational amplifier U1, an analog switch U2, a first temperature sensor, a second temperature sensor, a temperature reference circuit, an amplifying circuit and an amplifying reference circuit, wherein the temperature reference circuit comprises a first reference resistor and a second reference resistor, and the operational amplifier U1 comprises a first operational amplifier unit U1A, a second operational amplifier unit U1B and a third operational amplifier unit U1C.

Description of example 2 use:

the switch selection end of the analog switch U2 is used for being connected with the controller, and the output end of the second operational amplifier unit U1B is used for being connected with the controller.

The first platinum resistor PT1 is used for obtaining the water supply temperature, and the second platinum resistor PT2 is used for obtaining the backwater temperature.

The first temperature sensor and the second temperature sensor in the sampling device form a two-way temperature measuring circuit.

The temperature reference circuit in the sampling device comprises a first reference resistor and a second reference resistor, only two reference resistors are arranged on a temperature-sensitive device, other devices cannot influence the measurement result, and the temperature drift has little influence on the precision. The reference component used for calibration and the component having influence on temperature measurement precision only have the two reference resistances, so that the circuit cost is reduced.

The third operational amplifier unit U1C, namely an operational amplifier follower unit, is added to the reference voltage circuit of the amplifying reference circuit, namely the signal amplifying circuit, in the sampling device, so that the driving capability is increased, and finally, the linearity of the temperature measuring circuit is better, so that the circuit precision is increased.

The ZB switch impedance change of the analog switch U2 does not influence the current change by utilizing the constant current characteristic of the constant current circuit; by utilizing the characteristic of infinite input impedance of the operational amplifier, the ZA switch current of the analog switch U2 is zero, so that the influence of the analog switch U2 on temperature measurement is counteracted, and the precision is improved.

Example 3:

the utility model discloses a temperature drift resistant sampling device, which is different from embodiment 2 in that a first temperature sensor and a second temperature sensor are both nickel resistance temperature sensors, and the same points are not repeated.

Other embodiments may be used, such as increasing the number of temperature sensors as needed, to form a multi-path temperature measurement circuit.

The conception of the utility model:

the utility model aims to solve the defects or problems in the prior art, reduce the cost and improve the temperature measurement precision.

To achieve the above object:

the circuit adopts an improved constant current source circuit and a voltage reference circuit so as to increase the circuit precision.

And an analog switch circuit is adopted to realize multi-path temperature measurement.

By utilizing the characteristic of infinite input impedance of the integrated operational amplifier, the current of the voltage signal loop of the analog switch is zero, the influence of the internal resistance of the analog switch on temperature measurement is counteracted, and the precision is improved.

The two reference resistors are matched with the analog switch, the voltages of the two reference resistor loops are measured again when the temperature is measured each time, the resistance values of the two reference resistors are respectively the resistance value when the temperature is 0 ℃ and the resistance value when the temperature is 101.3 ℃, and real-time circuit parameters are calculated, so that the real-time calibration function is realized, and the problem of low temperature measurement precision caused by temperature drift of components is solved.

The reference component for calibration and the component which has influence on the temperature measurement precision have only two resistors, so that the circuit cost is reduced.

The inventors consider the technical contribution of the present utility model:

1. the constant current source is improved, so that the current output by the constant current source is less influenced by the load, and the circuit is simpler.

2. The voltage reference circuit is improved, the voltage follower is added, the reference voltage driving capability is enhanced, and finally the linearity of the temperature measuring circuit is better.

3. The analog switch and the reference resistor are utilized to calibrate circuit parameters during each temperature measurement, so that the requirement of the circuit on a constant current source is reduced, the circuit precision is improved, and the problem of low temperature measurement precision caused by temperature drift of components is solved.

4. Because the circuit has lower requirements on devices such as constant current sources, operational amplifiers and the like, the common devices can meet the requirements, so the circuit cost is reduced.

Compared with the comparison document 1, the technical scheme of the utility model has lower cost and higher precision. The temperature reference circuit of the reference 1 adopts three resistors, and the temperature reference circuit of the utility model adopts two resistors, which are high-precision resistors. The temperature drift is only related to two reference resistances, and the uncertainty is higher as the number of resistances is larger. The constant current circuit structure is different, and the comparison document 1 uses two triodes, but the precision is poorer. Compared with the existing constant current source circuit, the constant current source circuit has no triode.

Compared with the comparison file 2 and the comparison file 3, the utility model has different principles and poorer precision of the comparison file. The reasons for influencing the temperature measurement accuracy are 1 and the device accuracy. 2. And (5) temperature drift. And the temperature drift has a larger influence on the precision.

The temperature drift has little effect on the accuracy compared to the comparison document 2 or the comparison document 3 by the comparison document 1 or the circuit of the utility model. According to the technical scheme, the temperature-sensitive device has only two reference resistors, and other devices cannot influence the measurement result in temperature drift.

The technical scheme is as follows:

and each module of the circuit realizes principle analysis:

1. the device parameters in the circuit are as follows:

R1＝150KΩ，R2＝100KΩ，R3＝390Ω，R4＝0Ω，R5＝1KΩ，R6＝3KΩ，R7＝75KΩ，R8＝6.34KΩ，R9＝23.7KΩ，R10＝30KΩ。

C1＝0.1uF，C2＝0.1uF，C3＝0.1uF，C4＝0.1uF，C7＝0.1uF，C8＝0.1uF，C10＝0.1uF，C5＝1000pF，C6＝1000pF，C9＝0.22uF。

u2 is model 74HC4052, U1 is model LMV324, D1 is model ESD9L5.0ST5G, D2 is model ESD9L5.0ST5G, and D3 is model ESD9L5.0ST5G.

2. Constant current source circuit: the resistor r1=150kΩ, r2=100deg.kΩ, r6=3kΩ, and the operational amplifier u1a=lmv324. The resistors R1 and R2 divide the voltage to obtain a reference voltage, and the resistor R6 is a sampling resistor, and due to the virtual short characteristic of the operational amplifier, the constant current value of the constant current circuit=the current on the sampling resistor R6=the divided voltage values of the resistors R1 and R2/the resistance value of the sampling resistor R6.

3. Analog switching circuit: consisting of device u2=74 HC 4052. The analog switch is controlled by the MCU, and can switch the constant current output by the constant current circuit to a reference resistor R3=390 omega, R5=1K, a first path of measured platinum resistor and a second path of measured platinum resistor respectively according to the requirement; and the voltage signal outputted at each path due to the action of the constant current source is switched to the input end of the signal amplifying circuit.

4. A signal amplifying circuit: the amplifying circuit is composed of resistors r7=75kΩ, r8=6.33kΩ, an operational amplifier u1b=lmv324 and a reference voltage circuit. The function is to amplify each path of voltage output by the analog switch and transmit the amplified voltage to the MCU, namely the controller U3, and the model is STC8H8K64U.

5. Amplification reference circuit: consists of devices r9=23.7kΩ, r10=30kΩ, and an operational amplifier U1C. The reference voltage is obtained by dividing voltages of the resistors R9 and R10, and the reference voltage is realized by increasing driving capability of a voltage follower consisting of the operational amplifier U1C.

6. Resistance reference circuit: i.e. a temperature reference circuit, consisting of resistors r3=390 Ω, r5=1kΩ. The circuit is provided with voltage parameters at a temperature of 0 c and a temperature of 101.3 c.

The whole working principle of the circuit is as follows:

1. the analog switch circuit switches the constant current source to a reference resistor R5 loop, namely, the state when the platinum resistance temperature is 0 ℃, and the MCU acquires the voltage value output by the amplifying circuit. The voltage value output by the circuit when the temperature of the platinum resistor is 0 ℃.

2. The analog switch circuit switches the constant current source to a series circuit of reference resistors R3 and R5, namely, the state when the temperature of the platinum resistor is 101.3 ℃, and the MCU acquires the voltage value output by the amplifying circuit. The voltage value of the circuit output is the platinum resistor at the temperature of 101.3 ℃.

3. The analog switch circuit switches the constant current source to each tested platinum resistor loop, the example circuit is two paths of tested platinum resistors, if the number of analog switch paths is increased, the number of the tested platinum resistors can be increased, and the MCU acquires the voltage value output by the amplifying circuit. The voltage value output by the circuit when the measured platinum resistor is at the current temperature is obtained.

4. The current measured temperature value= (current measured platinum resistance voltage value-platinum resistance voltage value at temperature 0 ℃)/(platinum resistance voltage value at temperature 101.3 ℃ -platinum resistance voltage value at temperature 0 ℃)/101.3 was calculated.

5. And correcting the measured temperature by using a program platinum resistance linear correction algorithm.

The working process of the circuit comprises the following steps:

1. constant current circuit: the resistor comprises resistors R1, R2 and R6 and an operational amplifier U1A. The resistors R1 and R2 divide the voltage to obtain a reference voltage, and the resistor R6 is a sampling resistor, and due to the virtual short characteristic of the operational amplifier, the constant current value of the constant current circuit=the current on the sampling resistor R6=the divided voltage values of the resistors R1 and R2/the resistance value of the sampling resistor R6.

Because the current on the current sampling resistor R6 of the constant current circuit is completely equal to the current on the load output by the constant current circuit, no current branch loop exists in the middle, and therefore, the current on the load cannot be changed when the load is changed in the working voltage range. The precision of the constant current circuit is improved.

2. The MCU controls the analog switch U2 circuit to switch the constant current source to the reference resistor R5 loop, the platinum resistor is in a state when the temperature is 0 ℃, the voltage formed by the constant current source acting on the reference resistor R5 loop is amplified by the signal amplifying circuit and then sent to the ADC pin of the MCU, and the voltage acquired by the MCU is the voltage value output by the circuit when the platinum resistor is at the temperature of 0 ℃.

3. The MCU controls the analog switch U2 circuit to switch the constant current source to a state when the temperature of the platinum resistor is 101.3 ℃ in series connection with the reference resistors R3 and R5, the constant current source acts on the voltage formed by the series connection of the reference resistors R3 and R5, the voltage is amplified by the signal amplifying circuit and then sent to the ADC pin of the MCU, and the voltage acquired by the MCU is the voltage value output by the circuit when the temperature of the platinum resistor is 101.3 ℃.

4. The MCU controls the analog switch U2 circuit to switch the constant current source to each tested platinum resistor loop, the example circuit is 2-path tested platinum resistors, if the number of analog switch loops is increased, the number of the tested platinum resistors can be increased, multi-path temperature measurement is realized, the voltage formed by the constant current source acting on each tested platinum resistor loop is amplified by the signal amplifying circuit and then sent to the ADC pin of the MCU, and the voltage acquired by the MCU is the voltage value output by the circuit when the platinum resistor is at the current temperature.

5. The current measured temperature value= (current measured platinum resistance voltage value-platinum resistance voltage value at temperature 0 ℃)/(platinum resistance voltage value at temperature 101.3 ℃ -platinum resistance voltage value at temperature 0 ℃)/101.3 was calculated.

6. And correcting the measured temperature by using a program platinum resistance linear correction algorithm.

7. The circuit firstly tests the voltage output by the reference resistors R3 and R5 under the action of the constant current source when measuring the temperature, and calculates the measured problem by taking the two voltages as the reference, so that the temperature drift errors of all devices except the reference resistors R3 and R5 in the circuit are calibrated. The precision is improved and the cost is reduced due to the low requirements on the device.

The application scene is to measure the temperature from 0 ℃ to 100 ℃, and the resistance value of the third resistor R3 and the resistance value of the fifth resistor R5 are selected according to the requirement. The fifth resistor R5 corresponds to a reference resistor at 0 ℃, and the third resistor R3 and the fifth resistor R5 are connected in series to correspond to a reference resistor at 101.3 ℃.

Compared with the application scene, the temperature can be measured at 0 ℃ to 300 ℃, the resistance value of the third resistor R3 and the resistance value of the fifth resistor R5 are selected according to the requirement, and the resistance values are selected as the prior art and are not repeated.

Compared with the application scene, the temperature can be measured at 0 ℃ to 500 ℃, the resistance value of the third resistor R3 and the resistance value of the fifth resistor R5 are selected according to the requirement, and the resistance values are selected as the prior art and are not repeated.

1. The temperature reference circuit in the sampling circuit comprises a first reference resistor and a second reference resistor, only two reference resistors are arranged on a temperature sensitive device, other devices cannot influence a measurement result, and the temperature drift has little influence on accuracy. The reference component used for calibration and the component having influence on temperature measurement precision only have the two reference resistances, so that the circuit cost is reduced.

2. The constant current source circuit in the sampling device does not have any nonlinear devices such as branches, triodes and the like, the current on the sampling resistor is the current output by the constant current source, and the constant current is more accurate; the reference voltage circuit is added with the operational amplifier follower, so that the driving capability is stronger and the linearity is better. The constant current source circuit does not have any nonlinear devices such as branches, triodes and the like, the current on the sampling resistor is the current output by the constant current source, and the constant current is more accurate. The voltage reference circuit of the amplifying reference circuit, namely the signal amplifying circuit, is improved and added with a third operational amplifier unit U1C, namely an operational amplifier follower unit, so that the driving capability is improved, and finally, the linearity of the temperature measuring circuit is better, so that the circuit precision is improved. The ZB switch impedance change of the analog switch U2 does not influence the current change by utilizing the constant current characteristic of the constant current circuit; by utilizing the characteristic of infinite input impedance of the operational amplifier, the ZA switch current of the analog switch U2 is zero, so that the influence of the analog switch U2 on temperature measurement is counteracted, and the precision is improved.

3. And an analog switch U2 is adopted to realize two-way temperature measurement. PT1 is used for measuring the water supply temperature, and PT2 is used for measuring the backwater temperature. By adopting the cooperation of the two reference resistors and the analog switch, the voltage of the two reference resistor loops is re-measured when the temperature is measured each time, and the circuit parameters are calibrated when the temperature is measured each time, so that the requirement of the circuit on the constant current source is reduced, the circuit precision is improved, and the problem of low temperature measurement precision caused by temperature drift of components is solved.

4. The operational amplifier U1, the analog switch U2 and the controller U3 are adopted, the model of the operational amplifier U1 is LMV324, the model of the analog switch U2 is 74HC4052, the model of the controller U3 is STC8H8K64U, and the controller U3 is a common device, so that accurate temperature measurement can be realized, and the cost is low.

Claims

1. The utility model provides a sampling device that temperature drift is resisted, includes constant current reference voltage circuit, analog switch U2, first temperature sensor, second temperature sensor, temperature reference circuit, amplifying circuit and amplifying reference circuit, and first temperature sensor connects between the gating end of constant current reference voltage circuit and analog switch U2, and second temperature sensor connects between the gating end of constant current reference voltage circuit and analog switch U2, its characterized in that: the temperature reference circuit comprises a first reference resistor and a second reference resistor, the operational amplifier U1 comprises first to third operational amplifier units U1A to U1C, the amplifying circuit comprises a second operational amplifier unit U1B, the constant current reference voltage circuit is connected with the analog switch U2 through the first operational amplifier unit U1A, the constant current reference voltage circuit is connected with the gating end of the analog switch U2 through the second reference resistor and the first reference resistor in sequence, the gating end of the analog switch U2 is connected with the junction of the second reference resistor and the first reference resistor, the output end of the analog switch U2 is connected with the input end of the second operational amplifier unit U1B, and the amplifying reference circuit is connected with the second input end of the second operational amplifier unit U1B through the third operational amplifier unit U1C.

2. The temperature drift resistant sampling device of claim 1, wherein: the constant current reference voltage circuit and the first operational amplifier unit U1A form a constant current source circuit, the first reference resistor is used for providing a voltage parameter at a first temperature, the second reference resistor is used for providing a voltage parameter at a second temperature, the switch selection end of the analog switch U2 is used for being connected with a controller, and the output end of the second operational amplifier unit U1B is used for being connected with the controller.

3. The temperature drift resistant sampling device of claim 1, wherein: the constant-current reference voltage circuit comprises a first resistor R1, a second resistor R2 and a sixth resistor R6, wherein the first input end of the first operational amplifier unit U1A is connected with VCC through the first resistor R1, the first input end of the first operational amplifier unit U1A is grounded through the second resistor R2, the second input end of the first operational amplifier unit U1A is grounded through the sixth resistor R6, the gating end of the analog switch U2 is sequentially grounded through a first temperature sensor and the sixth resistor R6 and forms a first gating branch, the gating end of the analog switch U2 is sequentially grounded through the second temperature sensor and the sixth resistor R6 and forms a second gating branch, the gating end of the analog switch U2 is sequentially grounded through the first reference resistor, the second reference resistor and the sixth resistor R6 and forms a third gating branch, and the gating end of the analog switch U2 is sequentially grounded through the second reference resistor and the sixth resistor R6 and forms a fourth gating branch.

4. The temperature drift resistant sampling device of claim 1, wherein: the amplifying reference circuit comprises a ninth resistor R9 and a tenth resistor R10, the first input end of the third operational amplifier unit U1C is connected with VCC through the ninth resistor R9, the first input end of the third operational amplifier unit U1C is grounded through the tenth resistor R10, and the second input end of the third operational amplifier unit U1C is connected with the output end of the third operational amplifier unit U1C.

5. The temperature drift resistant sampling device of claim 1, wherein: the amplifying circuit further comprises a seventh resistor R7 and an eighth resistor R8, the output end ZA of the analog switch U2 is connected with the first input end of the second operational amplifier unit U1B, the output end of the third operational amplifier unit U1C is connected with the second input end of the second operational amplifier unit U1B through the eighth resistor R8, and the seventh resistor R7 is connected between the second input end of the second operational amplifier unit U1B and the output end of the second operational amplifier unit U1B.

6. A temperature measuring device resistant to temperature drift is characterized in that: the sampling device according to any one of claims 1 to 5, further comprising a controller U3, wherein the switch selection end of the analog switch U2 is connected to the controller, and the output end of the second op-amp unit U1B is connected to the controller.

7. The temperature measuring device of claim 6, wherein: the switch selection end of the analog switch U2 comprises a first switch selection end and a second switch selection end, the first switch selection end of the analog switch U2 is connected with the control end of the controller, and the second switch selection end of the analog switch U2 is connected with the control end of the controller.

8. The temperature measuring device of claim 6, wherein: the output end of the second operational amplifier unit U1B is connected with the controller through the fourth resistor R4.