Joule calibration circuit

Abstract

The utility model relates to the technical field of calibration experiments, and discloses a Joule calibration circuit, which comprises a singlechip control circuit, a power supply circuit, an analog to digital converter (ADC) voltage acquisition circuit, a digital to analog converter (DAC) voltage output circuit, a constant current source circuit, a relay control circuit and an isolating circuit. USB and 485 communication functions and JLINK online debugging are supported, a display screen serial port is configured to meet man-machine interaction, and a storage chip is reserved. Each single channel of the Joule calibration circuit meets the calibration functions of Joule resistance value detection, constant current output under set power and the like, circuit calibration current output meets high precision, and any 0-8 channels can be selected to work simultaneously when the circuit is applied.

Description

Technical Field

[0001] The utility model relates to the technical field of calibration experiments, in particular to a joule calibration circuit. Background Technique

[0002] Joule's law is a law that quantitatively explains the conversion of electrical energy into heat energy by a conduction current. The content is: the heat generated by a current passing through a conductor is proportional to the square of the current, proportional to the resistance of the conductor, and proportional to the time of power-on; joule calibration is often used in the instrument standard calibration experiment in the calorimetry field.

[0003] In the prior art, the joule calibration device uses a fixed joule resistor and calibration power to conduct a calibration experiment, and the resistance value of the joule resistor is affected to a certain extent by the change of the experimental temperature and the calibration power. When the calculated resistance value of the joule resistor is a fixed value, the heat capacity calibrated by the calibration device will deviate outside the acceptable range; in view of this, we propose a joule calibration circuit that can detect the calibration resistance value in real time. Content of the Utility Model

[0004] The purpose of the utility model is to provide a joule calibration circuit to solve the problems proposed in the above background technique.

[0005] To achieve the above purpose, the utility model provides the following technical solution: a joule calibration circuit, including a single-chip microcomputer control circuit, a power supply circuit, an ADC voltage acquisition circuit, a DAC voltage output circuit, a constant current source circuit, a relay control circuit and an isolation circuit. The power supply circuit provides electrical energy for the joule calibration circuit. The single-chip microcomputer control circuit includes a control chip U1. The 22nd terminal of the control chip U1 is electrically connected to the VCC3.3 terminal. The VCC3.3 terminal is electrically connected to one end of a resistor R1. The other end of the resistor R1 is electrically connected to one end of a resistor C8. The other end of the resistor C8 is grounded.

[0006] Optionally, the model of the control chip U1 is STM32F103VCT6.

[0007] Optionally, the power supply circuit includes a wiring terminal P3 and a wiring terminal CN3. The model of the wiring terminal P3 is WJ15EDGRC3.81-2P. The 1st terminal of the wiring terminal P3 is electrically connected to the +5V terminal. The 2nd terminal of the wiring terminal P3 is grounded. The 2nd terminal of the wiring terminal CN3 is electrically connected to the VCC terminal. The 1st terminal and the 3rd terminal of the wiring terminal CN3 are both electrically connected to the AGND terminal. The 4th terminal of the wiring terminal CN3 is electrically connected to the 35V terminal.

[0008] Optionally, the ADC voltage acquisition circuit includes a signal isolation chip U24. The model of the signal isolation chip U24 is AD7124-8BCPZ.

[0009] Optionally, the DAC voltage output circuit includes an output chip U29, the model of the output chip U29 is 160U30, and the 8th terminal of the output chip U29 is grounded. The 9th terminal of the output chip U29 is electrically connected to the AGND terminal, the 1st terminal of the output chip U29 is electrically connected to the VCC3.3 terminal, the 1st terminal of the output chip U29 is electrically connected to one end of a capacitor C39, and the other end of the capacitor C39 is grounded. The 16th terminal of the output chip U29 is electrically connected to one end of a capacitor C38, and the other end of the capacitor C38 is electrically connected to the AGND terminal.

[0010] Optionally, the relay control circuit includes a relay K1. The 5th terminal of the relay K1 is electrically connected to one end of a resistor R18, the other end of the resistor R18 is electrically connected to one end of a capacitor C73, and the other end of the capacitor C73 is grounded. The 4th terminal of the relay K1 is electrically connected to one end of a resistor R19, the other end of the resistor R19 is electrically connected to one end of a capacitor C75, and the other end of the capacitor C75 is grounded.

[0011] Compared with the prior art, the present invention provides a joule calibration circuit, which has the following beneficial effects:

[0012] This joule calibration circuit can satisfy the joule calibration work of 8 channels simultaneously, support USB, 485 communication functions and JLINK online debugging, configure a display screen serial port to meet human-computer interaction, and has a spare storage chip. Each single channel of the joule calibration circuit can satisfy calibration functions such as joule resistance value detection and constant current output under a set power. The calibrated current output of the circuit meets a high precision, and any number of 0 to 8 channels can be selected to work simultaneously when the circuit is applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a partial structural schematic diagram of the single-chip microcomputer control circuit of the present invention;

[0014] Figure 2 It is a partial structural schematic diagram of the single-chip microcomputer control circuit of the present invention;

[0015] Figure 3 It is a partial structural schematic diagram of the power supply circuit of the present invention;

[0016] Figure 4 It is a partial structural schematic diagram of the power supply circuit of the present invention.

[0017] Figure 5 It is a partial structural schematic diagram of the power supply circuit of the present invention

[0018] Figure 6 It is a structural schematic diagram of the ADC voltage acquisition circuit of the present invention.

[0019] Figure 7 Schematic diagram of the DAC voltage output circuit structure of the present utility model

[0020] Figure 8 Schematic diagram of the structure of the constant current source circuit of the present utility model;

[0021] Figure 9 Schematic diagram of the relay control circuit structure of the present utility model; Specific embodiments

[0022] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0023] As Figures 1-9 shown, the present utility model provides a technical solution: a joule calibration circuit, including a single-chip microcomputer control circuit, a power supply circuit, an ADC voltage acquisition circuit, a DAC voltage output circuit, a constant current source circuit, a relay control circuit and an isolation circuit. The power supply circuit provides electrical energy for the joule calibration circuit. The single-chip microcomputer control circuit includes a control chip U1. The 22nd terminal of the control chip U1 is electrically connected to the VCC3.3 terminal. The VCC3.3 terminal is electrically connected to one end of the resistor R1. The other end of the resistor R1 is electrically connected to one end of the resistor C8. The other end of the resistor C8 is grounded. The model of the control chip U1 is STM32F103VCT6.

[0024] The power supply circuit includes a wiring terminal P3 and a wiring terminal CN3. The model of the wiring terminal P3 is WJ15EDGRC3.81-2P. The 1st terminal of the wiring terminal P3 is electrically connected to the +5V terminal. The 2nd terminal of the wiring terminal P3 is grounded. The 2nd terminal of the wiring terminal CN3 is electrically connected to the VCC terminal. The 1st terminal and the 3rd terminal of the wiring terminal CN3 are both electrically connected to the AGND terminal. The 4th terminal of the wiring terminal CN3 is electrically connected to the 35V terminal.

[0025] The ADC voltage acquisition circuit includes a signal isolation chip A1. The model of the signal isolation chip A1 is AD7124-8BCPZ.

[0026] The DAC voltage output circuit includes output chip U29, the model of output chip U29 is 160U30, and the 8th terminal of output chip U29 is grounded. The 9th terminal of output chip U29 is electrically connected to the AGND terminal, the 1st terminal of output chip U29 is electrically connected to the VCC3.3 terminal, the 1st terminal of output chip U29 is electrically connected to one end of capacitor C39, and the other end of capacitor C39 is grounded. The 16th terminal of output chip U29 is electrically connected to one end of capacitor C38, and the other end of capacitor C38 is electrically connected to the AGND terminal.

[0027] The relay control circuit includes relay K1. The 5th terminal of relay K1 is electrically connected to one end of resistor R18, the other end of resistor R18 is electrically connected to one end of capacitor C73, and the other end of capacitor C73 is electrically connected to the AGND terminal. The 4th terminal of relay K1 is electrically connected to one end of resistor R19, the other end of resistor R19 is electrically connected to one end of capacitor C75, and the other end of capacitor C75 is electrically connected to the AGND terminal.

[0028] As an application of this embodiment:

[0029] The current output power supply circuit is composed of 3-way 3.3V outputs and 1-way 5V output. The 3-way 3.3V power supplies respectively supply power to the single-chip microcomputer control circuit and the communication circuit (VCC3.3), the ADC voltage acquisition circuit and the isolation chip (IO3.3V), and the DAC voltage output circuit and the reference voltage circuit (3.3V). The purpose of outputting the same 3.3V voltage in three ways is to completely isolate the single-chip microcomputer control circuit and the analog circuit parts, avoid the analog signals of acquisition and output from interfering with the single-chip microcomputer, and at the same time ensure the accuracy of analog signal acquisition and output. As Figure 4 shown, U24 is a 24-bit, low-noise, low-power integrated PGA, using 8-way differential small-signal inputs to meet the input voltage acquisition accuracy; C66 and C70 are decoupling capacitors for the REGCAPD and REGCAPA pins, decoupled to the analog ground AGND; REFIN+ and REFIN- are externally connected to the reference voltage VREF 2.5V, and the device can work with a reference voltage within the range of 1V to 3.3V externally connected to AVDD; the SYNC# pin is externally connected to a 10kΩ pull-up resistor, and when it is at a high level, it enables the digital filters and analog modulators of multiple AD7124-8 devices to be synchronized for input, and vice versa for reset; the CS, SCLK, DIN, and DOUT / RDY# pins are used for ADC acquisition data transmission with the single-chip microcomputer, and are respectively configured as chip select input, clock input, serial data input, and serial data output in the program; AIN0 to AIN15 are externally connected to the ADC acquisition control circuit to complete 8-channel voltage data acquisition in a differential form.

[0030] Before the Joule calibration circuit starts to work properly, the accurate resistance value of the Joule resistor needs to be obtained. Since its resistance value changes with the experimental constant temperature, the circuit is designed with an ADC voltage acquisition circuit to measure the resistance value of the Joule resistor before each calibration experiment.

[0031] The ADC acquisition circuit is mainly controlled by the AD7124-8BCPZ chip to meet the function of 8-channel voltage acquisition. The ADUM1441ARQZ isolation chip is used to ensure the transmission of the acquisition signal between the single-chip microcomputer and this chip, avoiding interference.

[0032] When the host computer issues the calibration power P JC and the calibration time T JC , the single-chip microcomputer calculates the ADC acquisition voltage value to obtain the resistance value R val of the current Joule resistor. Then, using the electric power calculation formula, the current value I SET that the Joule calibration module needs to output is obtained, and the analog voltage quantity that the DAC circuit needs to output is calculated inversely.

[0033]

[0034] The DAC output circuit is composed of the DAC8830ID analog signal output chip and its follower AD8629ARZ, and the voltage reference chip ADR4525ARZ and its follower provide a 2.5V reference voltage.

[0035] As Figure 7 shown, U27 is a 16-bit, low-power voltage output digital-to-analog converter, and the output analog voltage value range is from 0 to the VREF reference voltage of 2.5V. Therefore, the analog voltage calculation formula is as follows:

[0036]

[0037] where V REF = 2.5V, R SAMPLE = 25Ω, and I SET is the current value that needs to be output for this calibration; VDD is externally connected to a 3.3V power supply as the working voltage of the analog circuit; the SDI, CS#, and SCLK pins are used for data transmission of the DAC voltage between the single-chip microcomputer, and are respectively configured as serial data input, chip select input, and clock input in the program; the VOUT pin is externally connected to U26 as a voltage follower, that is, a buffer amplifier. The input and output voltage values of the follower are the same, and it has a lower output impedance, which can drive the subsequent load more effectively and also isolate the interference of the subsequent stage to the previous-stage chip U27.

[0038] As Figure 8As shown, the main function of the constant current source circuit is to convert the analog voltage output by the DAC circuit into a current signal, and obtain the theoretical Joule heat by controlling the current value input to the Joule resistor and the output current time.

[0039] When the voltage value VREF_OUT of the analog voltage signal output by the DAC circuit is U and is input to the constant current source circuit, it is divided by R39 to U / 2, and then converted back to the voltage value U through the inverting amplifier U45.2 in the AD8629ARZ op amp. The amplification factor is calculated as follows:

[0040]

[0041] Where R 36 = R 37 = 10 kΩ, so the amplification factor A u = 2. R36 and R37 are high-precision, low-temperature-drift R0805 package resistors; Q3 is an NPN transistor, which cooperates with U45.2 to achieve stable output current of the constant current source. When the voltage of the current sampling resistor changes, this change will be fed back to the inverting input terminal of U45.2. At this time, the voltage difference from the non-inverting input terminal is amplified and output by the op amp, and the output controls the base current of Q3, and the voltage drop between the collector and the emitter changes accordingly. Finally, the function of keeping the voltage of the sampling resistor constant is realized; the output current sampling resistor is composed of two 50 Ω high-precision, low-temperature-drift RJ711 package resistors in parallel, so the current sampling resistor value is 25 Ω. Therefore, when the DAC voltage output circuit outputs the maximum voltage value of 2.5 V, the constant current source circuit has a maximum output current of 0.1 A.

[0042] The relay control circuit consists of two parts. The first part has 8 relays that respectively control the voltage acquisition of 8 channels. When the module acquires the voltage value of the Joule resistor, it controls the acquisition signal and the small current transmission of the constant current source; the second part has 4 single-pole double-throw relays that control the current output of the constant current source. After the first part finishes the acquisition, the relays will no longer be turned on, and the output and output time are controlled by the relays in the second part.

[0043] The above has generally described the present invention in detail, but based on the present invention, some modifications or improvements can be made, which are obvious to those of ordinary skill in the art. Therefore, the modifications or improvements that do not depart from the spirit of the present invention are all within the protection scope of the present invention.

Claims

1. A joule calibration circuit, characterized in that: It includes a single-chip microcomputer control circuit, a power supply circuit, an ADC voltage acquisition circuit, a DAC voltage output circuit, a constant current source circuit, a relay control circuit and an isolation circuit. The power supply circuit provides electrical energy for the joule calibration circuit. The single-chip microcomputer control circuit includes a control chip U1. The 22nd terminal of the control chip U1 is electrically connected to the VCC3.3 terminal. The VCC3.3 terminal is electrically connected to one end of a resistor R1. The other end of the resistor R1 is electrically connected to one end of a resistor C8. The other end of the resistor C8 is grounded.

2. The joule calibration circuit according to claim 1, characterized in that: The model of the control chip U1 is STM32F103VCT6.

3. The joule calibration circuit according to claim 1, characterized in that: The power supply circuit includes a terminal block P3 and a terminal block CN3. The model of the terminal block P3 is WJ15EDGRC3.81-2P. The 1st terminal of the terminal block P3 is electrically connected to the +5V terminal. The 2nd terminal of the terminal block P3 is grounded. The 2nd terminal of the terminal block CN3 is electrically connected to the VCC terminal. The 1st terminal and the 3rd terminal of the terminal block CN3 are both electrically connected to the AGND terminal. The 4th terminal of the terminal block CN3 is electrically connected to the 35V terminal.

4. The joule calibration circuit according to claim 1, characterized in that: The ADC voltage acquisition circuit includes a signal isolation chip U24. The model of the signal isolation chip U24 is AD7124-8BCPZ.

5. A joule calibration circuit according to claim 1, wherein: The DAC voltage output circuit includes an output chip U29. The model of the output chip U29 is 160U30. The 8th terminal of the output chip U29 is grounded. The 9th terminal of the output chip U29 is electrically connected to the AGND terminal. The 1st terminal of the output chip U29 is electrically connected to the VCC3.3 terminal. The 1st terminal of the output chip U29 is electrically connected to one end of a capacitor C39. The other end of the capacitor C39 is grounded. The 16th terminal of the output chip U29 is electrically connected to one end of a capacitor C38. The other end of the capacitor C38 is electrically connected to the AGND terminal.

6. A joule calibration circuit according to claim 1, wherein: The relay control circuit includes a relay K1. The 5th terminal of the relay K1 is electrically connected to one end of a resistor R18. The other end of the resistor R18 is electrically connected to one end of a capacitor C73. The other end of the capacitor C73 is grounded. The 4th terminal of the relay K1 is electrically connected to one end of a resistor R19. The other end of the resistor R19 is electrically connected to one end of a capacitor C75. The other end of the capacitor C75 is grounded.

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