CN113820355A - 3 omega test bed and test method thereof - Google Patents
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Abstract
The invention discloses a 3 omega test bed and a test method thereof, comprising a data acquisition card, a power amplification circuit, a voltage source-to-current source circuit and a heater circuit; the data acquisition card transmits the waveform of the output voltage generated by the programming software to the input end of the power amplification circuit through the analog output end; the power amplification circuit accesses the voltage signal after power amplification to the voltage source-current source conversion circuit, the current of the feedback resistor is constant, the converted current source is connected to the two ends of the heater circuit, and the voltage of the voltage end of the heater circuit is output to the analog input end of the data acquisition card. Compared with the traditional 3 omega test bed, the invention removes a high-resolution current source and a high-precision phase-locked amplifier, uses programming software to generate a voltage waveform to be output, and outputs the generated voltage waveform by using a control part configured and controlled in a data acquisition card driving program, thereby realizing automatic measurement and having high measurement precision.
Description
Technical Field
The invention relates to the field of thermophysical property testing, in particular to a 3 omega test bed and a testing method thereof.
Background
The existing methods for measuring the thermophysical properties of materials mainly include the traditional cut-bar method, the optical TDTR (time domain thermal reflection) method, the electrical signal measurement method and the like.
The cut-bar method is low in cost, but cannot measure microscale film materials, can only measure body state materials, and cannot be used in the microscale design field;
the optical TDTR method can measure the form and two-dimensional material, the test process is simple, but the construction cost is extremely expensive, a crystal laser transmitter required by a traditional TDTR test bed consumes more than million RMB, and the optical path adjusting part has extremely high professional requirements on operators;
the 3 omega measuring method is a measuring method for measuring the thermal physical properties of materials by using electric signals, the sample preparation difficulty is low, the thermal physical properties of the physical state, the film and the biological tissue sample can be measured, the traditional 3 omega test bed mainly comprises a current source, a heater, a sample placing table and a phase-locked amplifier, and the construction cost of the whole test bed is still very high.
The testing method is mostly existed in research and development departments of laboratories of colleges and universities and advanced technology enterprises, expensive import instruments are required to be built, and in sensitive industries in China, such as chip testing, military aviation and other fields, due to the requirement of American process, the existing current source and the phase-locked amplifier face the risk of being unusable, and the test bed directly faces the risk of being unusable in the future. In addition, in engineering practice, the above instruments are not only too expensive but also have excessive performance, and require professional operation, which is not favorable for engineering cost control.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the invention aims to solve the defects in the prior art and provides a 3 omega test bed for replacing the current source and a phase-locked amplifier and a test method thereof.
The technical scheme of the invention is as follows: the invention relates to a 3 omega test bed, which comprises a data acquisition card, a power amplification circuit, a voltage source-to-current source circuit and a heater circuit, wherein the data acquisition card is connected with the power amplification circuit;
the data acquisition card transmits the waveform of the output voltage generated by the programming software to the input end of the power amplification circuit through the analog output end; the power amplification circuit accesses the voltage signal with amplified power to a voltage source-current source conversion circuit, the current of the feedback resistor is constant, the converted current source is connected to two ends of the heater circuit, and the voltage of the voltage end of the heater circuit is output to the analog input end of the data acquisition card.
Further, the power amplifier circuit comprises a power amplifier and a resistor RGAnd a feedback resistor RF(ii) a V of the power amplifierinThe + end is grounded, and the input signal is connected in series with RGV connected to said power amplifierinEnd at V of the power amplifierin-and VoutEnd access feedback resistor RF。
Furthermore, the voltage source-to-current source circuit comprises a first amplifier, a second amplifier and a resistor R1A feedback resistor R2Resistance R3And a heater; the first amplifier and the second amplifier are connected in series;
v of the first amplifierinThe + end is grounded, and the input signal is connected in series with R1V connected to the first amplifierin-end, V of said first amplifierinV with the first amplifieroutEnd access feedback resistor R2；
V of the second amplifierinTerminal + is grounded, V of the first amplifieroutSignal series connection R3V connected to the second amplifierin-end, V of said second amplifierinV with a second amplifieroutThe end is connected to a heater.
Further, the data acquisition card is a USB-6218 data acquisition card;
the power amplifier is an OPA452 power amplifier;
the first amplifier and the second amplifier are muA 741 amplifiers.
The invention also discloses a testing method of the 3 omega test bed, and the 3 omega test bed comprises the following steps:
firstly, voltage output is realized; generating a voltage waveform to be output by programming software, and outputting the generated voltage waveform signal to a power amplification circuit through an analog output port of a data acquisition card;
step two, the voltage waveform signal after passing through the power amplifying circuit has the voltage gain of-RF/RG；
Thirdly, connecting the voltage waveform signal after power amplification to a voltage source-to-current source circuit, connecting the converted current source at two ends of the heater, and driving the heater in the heater circuit to work as the current source; wherein, the current magnitude of the current source is determined by the ratio of the input voltage to the resistances of each stage,
step four, outputting the voltage terminal of the heater to the analog input end of the data acquisition card;
step five, setting the analog input of the data acquisition card by using programming software, setting the start trigger to ensure that the analog output is the same as the start moment of the analog input, and ensuring that the phase relation between the input signal and the output signal is fixed, thereby determining the effective values and phases of the frequency multiplication signals 1 and 3;
reading the waveform of the analog input end, generating corresponding frequency 1 multiplication and frequency 3 multiplication reference signals and the frequency 1 multiplication and frequency 3 multiplication reference signals after 90-degree phase shift according to the waveform of the input signal, and multiplying the frequency 1 multiplication and frequency 3 multiplication reference signals by the input signal respectively to realize the function of the phase-sensitive detector; step seven, inputting the processed signals into a digital low-pass filter, filtering high-frequency noise signals to obtain direct-current signals with input signal effective values and phase information, performing mathematical processing on the direct-current signals obtained before and after phase shifting, and calculating effective values and phases of 1-frequency-doubled and 3-frequency-doubled signals;
and step eight, changing the frequency of the output signal, measuring the frequency multiplication signals 1 and 3 for multiple times, drawing a voltage-frequency relation graph, fitting a logarithm of the frequency multiplication signals 3 to a frequency relation curve of a proper frequency section to obtain a slope, calculating a formula of the thermal conductivity according to a 3 omega method, and calculating the thermal conductivity of the measured sample.
Further, the voltage gain-RF/RGSet to-1.
Compared with the prior art, the invention has the beneficial effects that:
compared with the traditional 3 omega test bed, the high-resolution current source and the high-precision phase-locked amplifier are removed, the saved direct economic cost is more than 10 ten thousand, programming software is used for generating a voltage waveform to be output, the generated voltage waveform is output by using a control part of the data acquisition card configured and controlled in a data acquisition card driving program, automatic measurement is realized, labor force is liberated, operation of professional scientific research personnel is not needed, and the final measurement result is less than 13% of error compared with the traditional 3 omega measurement method; besides the price advantage, the system also has the advantages of portability, easy use, high space utilization rate and the like.
Drawings
FIG. 1 is a schematic circuit diagram of a 3 ω test stand according to the present invention;
FIG. 2 is a circuit diagram of a power amplifier circuit according to the present invention;
FIG. 3 is a circuit diagram of a voltage-to-current source circuit according to the present invention;
FIG. 4 is a graph comparing the results of the conventional 3 ω method and the 3 ω method of this patent on the thermal conductivity of bismuth ferrite.
Detailed Description
For the understanding of the present invention, the following detailed description will be given with reference to the accompanying drawings, which are provided for the purpose of illustration only and are not intended to limit the scope of the present invention.
As shown in FIGS. 1-3, the programming software mainly used in the invention is LabVIEW, has high compatibility with a USB-6218 data acquisition card, and is also the core of the automatic control of the whole test bed.
Firstly, voltage output is realized, voltage waveform to be output is generated by LabVIEW, and then USB-6218 analog output is set by configuring and controlling an NI-DAQmax control of a data acquisition card in a data acquisition card driver of an NI company, so that the voltage waveform generated by the NI-DAQmax control is output.
Then the output voltage waveform is connected to the input end of a power amplifying circuit of the power amplifier OPA452, and after passing through the power amplifying circuit, the voltage gain is-RF/RGPower is amplified, maximum output powerThe flow may be up to 50 mA.
Then the voltage signal after amplifying power is connected to a circuit for converting the mu a741 voltage source into a current source, the current of the feedback resistor is constant due to the virtual short and virtual break principle of the amplifier, and can be used as a current source to drive a heater on a sample, the current of the current source is determined by the ratio of the input voltage to the resistors of each stage,
and finally, connecting the converted current source at two ends of the heater, and outputting the voltage at the voltage end of the heater to the analog input end of the USB-6218 data acquisition card.
Setting USB-6218 analog input by using NI-DAQmax control of LabVIEW, setting a start trigger, making the analog output and the analog input start time the same, ensuring that the phase relation of the input signal and the output signal is fixed, and determining the effective value and the phase of the 1 frequency doubling signal and the 3 frequency doubling signal. And reading the waveform of the analog input end, generating corresponding frequency 1 multiplication and frequency 3 multiplication reference signals and the frequency 1 multiplication and frequency 3 multiplication reference signals after 90-degree phase shift according to the waveform of the input signal, and multiplying the frequency 1 multiplication and frequency 3 multiplication reference signals by the input signal respectively to realize the function of the phase-sensitive detector. Inputting the processed signal into a digital low-pass filter, filtering high-frequency noise signals to obtain a direct current signal with an input signal effective value and phase information, performing mathematical processing on the direct current signal obtained before and after phase shifting, and calculating effective values and phases of frequency 1 doubling signals and frequency 3 doubling signals.
And then changing the frequency of the output signal, measuring the 1 frequency doubling signal and the 3 frequency doubling signal for multiple times, drawing a voltage-frequency relation graph, fitting a logarithm of the 3 frequency doubling signal with a relation curve of the frequency by taking a proper frequency section to obtain a slope, and calculating the thermal conductivity of the measured sample according to a formula of calculating the thermal conductivity by a 3 omega method.
According to the used devices, a guiding method for designing the circuit and writing the program is given.
As shown in FIG. 2, the power amplifier circuit of the present invention includes an OPA452 power amplifier and a resistor RGAnd a feedback resistor RF；Wherein V of OPA452 power amplifierinThe + end is grounded, and the input signal is connected in series with RGV of access power amplifierinEnd at V of the power amplifierin-and VoutEnd access feedback resistor RF。
As shown in fig. 3, the voltage-to-current source circuit of the present invention includes: two muA 741 amplifiers, resistor R1A feedback resistor R2Resistance R3And a heater;
v of the first muA 741 AmplifierinThe + end is grounded, and the input signal is connected in series with R1V connected into mu A741 amplifierinAt the end, V at the first μ A741 amplifierin-and VoutEnd access feedback resistor R2。
Vin + of the second μ A741 amplifier is connected to ground, V of the first μ A741 amplifieroutSignal series connection R3V connected into a second muA 741 amplifierinAt the end, V at a second μ A741 amplifierin-and VoutThe end is connected to a heater.
In the power amplifying circuit, the maximum output voltage of the OPA452 is 80V, the maximum output current is 50mA, since we will convert the voltage into the current in the following, the voltage gain here is not too large, usually set to-1, and the regulated voltage is mostly obtained by directly setting the analog output waveform of the USB-6218 in LabVIEW.
In the voltage source to current source circuit, because the output voltage range of μ a741 is ± 14V, and the voltage source to current source circuit needs to be amplified in two stages, when designing the resistance value of the resistor, attention needs to be paid to the amplification factor of the first stage of amplification circuit, and the amplification factor does not exceed the output range of μ a741, and after determining the multiplying factor of the lower voltage source to current source, R can be increased1The resistance value of the first stage amplifier circuit is reduced.
In the function of the phase-locked amplifier realized by the programming software and the data acquisition card, the cut-off frequency of the digital low-pass filter is set to be lower along with the reduction of the signal frequency, and is used for filtering small-frequency noise signals near low-frequency signals, but the cut-off frequency is not set to be too low, firstly, the frequency of a reference signal and the frequency of an input signal are usually difficult to be set to be completely the same frequency, so that the signals passing through the digital phase-sensitive detector are not ideal direct current signals, usually small-frequency signals with the magnitude of 0.001Hz, if the cut-off frequency of the low-pass filter is set to be too small, useful signals are partially filtered, errors are generated, secondly, the cut-off frequency of the small low-pass filter can cause a large time constant, the time for waiting for the signals to be stable is long, and finally the efficiency of measurement is not high.
After a relation curve of a frequency doubling signal and frequency is obtained, a frequency range for calculating a logarithm fitting curve coefficient needs to be determined, the frequency range is related to sample thermal conductivity, sample thickness and heater line width, thermal penetration depth needs to be estimated, the thermal penetration depth is far larger than half width of a heater and smaller than the sample thickness, a proper frequency range is determined, generally, a sample with small thermal conductivity needs low measurement frequency, and a sample with large thermal conductivity needs high measurement frequency.
The frequency range of the test bed is limited by the sampling rate of 250kS/s of the analog output and the analog input of the USB-6218, and the test bed measures the frequency range of 0Hz to 41.66kHz according to the Nyquist sampling law.
As shown in FIG. 4, taking a sample of bismuth ferrite 2mm in thickness as an example, the heater width was 20 μm, the voltage segment length was 1500 μm, the resistance was 29. omega., and the dR/dT ratio of the heater at 300K was 0.0694. omega./K. And a USB-6218 data acquisition card is used for outputting sine alternating current with the amplitude of 1.54V at an analog output end. Through a power amplifying circuit, R in the power amplifying circuitF＝RGThe voltage gain is-1 at 5k Ω, and a sinusoidal alternating current with an amplitude of 1.54V and a phase of 180 ° is output. Through a voltage source to current source circuit, in which P1＝33kΩ，R3＝330Ω，R2100k omega, the conversion rate of voltage to current is-0.00918A/V, the final effective value of output current is 10mA, the heater is connected, the voltage section of the heater is connected to the analog input end of the data acquisition card, the relationship curve of 3 frequency doubling signals and frequency is obtained by processing the voltage section of the heater by the programming software and the data acquisition card, the frequency range is 1Hz-100Hz, and dV is obtained by logarithmic fitting3ω(lf), the final calculated thermal conductivity of the bismuth ferrite at 300K is 2.278W/(m.K), which is 9.82% compared with the thermal conductivity 2.526W/(m.K) of the bismuth ferrite measured by the traditional 3 omega method at 300KThe error of (2).
The above embodiments are merely illustrative of the technical concept and structural features of the present invention, and are intended to be implemented by those skilled in the art, but the present invention is not limited thereto, and any equivalent changes or modifications made according to the spirit of the present invention should fall within the scope of the present invention.
Claims (6)
1. A 3 ω test stand characterized in that: the device comprises a data acquisition card, a power amplification circuit, a voltage source-to-current source circuit and a heater circuit;
the data acquisition card transmits the waveform of the output voltage generated by the programming software to the input end of the power amplification circuit through the analog output end; the power amplification circuit accesses the voltage signal with amplified power to a voltage source-current source conversion circuit, the current of the feedback resistor is constant, the converted current source is connected to two ends of the heater circuit, and the voltage of the voltage end of the heater circuit is output to the analog input end of the data acquisition card.
2. The 3 ω test stand according to claim 1, characterized in that: the power amplifier circuit comprises a power amplifier and a resistor RGAnd a feedback resistor RF(ii) a V of the power amplifierinThe + end is grounded, and the input signal is connected in series with RGV connected to said power amplifierinEnd at V of the power amplifierin-and VoutEnd access feedback resistor RF。
3. 3 ω -test stand according to claim 2, characterized in that: the voltage source-to-current source circuit comprises a first amplifier, a second amplifier and a resistor R1A feedback resistor R2Resistance R3And a heater; the first amplifier and the second amplifier are connected in series;
v of the first amplifierinThe + end is grounded, and the input signal is connected in series with R1V connected to the first amplifierin-an end of the device,v of the first amplifierinV with the first amplifieroutEnd access feedback resistor R2；
V of the second amplifierinTerminal + is grounded, V of the first amplifieroutSignal series connection R3V connected to the second amplifierin-end, V of said second amplifierinV with a second amplifieroutThe end is connected to a heater.
4. A 3 ω -test stand according to claim 3, characterized in that:
the data acquisition card is a USB-6218 data acquisition card;
the power amplifier is an OPA452 power amplifier;
the first amplifier and the second amplifier are muA 741 amplifiers.
5. A test method of a 3 omega test bed is characterized in that: use of a 3 ω -bench according to any of the claims 1 to 4, comprising the steps of:
firstly, voltage output is realized; generating a voltage waveform to be output by programming software, and outputting the generated voltage waveform signal to a power amplification circuit through an analog output port of a data acquisition card;
step two, the voltage waveform signal after passing through the power amplifying circuit has the voltage gain of-RF/RG；
Thirdly, connecting the voltage waveform signal after power amplification to a voltage source-to-current source circuit, connecting the converted current source at two ends of the heater, and driving the heater in the heater circuit to work as the current source; wherein, the current magnitude of the current source is determined by the ratio of the input voltage to the resistances of each stage,
step four, outputting the voltage terminal of the heater to the analog input end of the data acquisition card;
step five, setting the analog input of the data acquisition card by using programming software, setting the start trigger to ensure that the analog output is the same as the start moment of the analog input, and ensuring that the phase relation between the input signal and the output signal is fixed, thereby determining the effective values and phases of the frequency multiplication signals 1 and 3;
reading the waveform of the analog input end, generating corresponding frequency 1 multiplication and frequency 3 multiplication reference signals and the frequency 1 multiplication and frequency 3 multiplication reference signals after 90-degree phase shift according to the waveform of the input signal, and multiplying the frequency 1 multiplication and frequency 3 multiplication reference signals by the input signal respectively to realize the function of the phase-sensitive detector;
step seven, inputting the processed signals into a digital low-pass filter, filtering high-frequency noise signals to obtain direct-current signals with input signal effective values and phase information, performing mathematical processing on the direct-current signals obtained before and after phase shifting, and calculating effective values and phases of 1-frequency-doubled and 3-frequency-doubled signals;
and step eight, changing the frequency of the output signal, measuring the frequency multiplication signals 1 and 3 for multiple times, drawing a voltage-frequency relation graph, fitting a logarithm of the frequency multiplication signals 3 to a frequency relation curve of a proper frequency section to obtain a slope, calculating a formula of the thermal conductivity according to a 3 omega method, and calculating the thermal conductivity of the measured sample.
6. The 3 ω test stand according to claim 5, characterized in that: the voltage gain-RF/RGSet to-1.
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