Quantitative compensation time difference measurement method for carbon dioxide concentration

Abstract

The invention relates to a quantitative compensation time difference measurement method for carbon dioxide concentration, and belongs to the technical field of carbon dioxide concentration measurement by using a time difference method. According to the technical scheme, phase discrimination is carried out on the phase difference between signals according to the phase relation of periodic changes between a fixed-frequency pulse signal f1 and an adjustable-frequency pulse signal f2, a whole-period phase discrimination voltage sequence is formed within the timing time, the change of the phase discrimination voltage is observed, quantitative compensation is carried out, and the frequency value of the adjustable-frequency pulse signal is adjusted. Furthermore, a full-period phase discrimination voltage sequence is quickly obtained within the timing time, the counting value of the frequency-adjustable pulse signal f2 by the measuring system is n, and the time difference t = n / f2 is solved. According to the invention, the counting error of + / -1 pulse is overcome by utilizing the characteristic of phase difference change between pulse signals, and the rapid quantitative compensation time difference measurement of the changed carbon dioxide concentration is realized.

Description

Technical Field

[0001] The present invention relates to a quantitative compensated time difference measurement method for carbon dioxide concentration. The method utilizes the periodically changing phase relationship between a fixed frequency pulse signal and an adjustable frequency pulse signal to perform phase discrimination on the phase difference between the signals, and forms a full cycle phase discrimination voltage sequence within the timing time to achieve high-precision carbon dioxide concentration measurement. The method belongs to the technical field of carbon dioxide concentration measurement using the time difference method. Background Art

[0002] Carbon dioxide concentration measurement is widely used in animal husbandry, industry, agriculture, pharmaceuticals, municipal administration, sewage treatment and other fields. Carbon dioxide monitoring is very practical and valuable. It can help understand and improve air quality, save energy and reduce emissions, monitor industrial emissions, evaluate ecosystems, etc. The main principle of using the time difference method to measure carbon dioxide concentration is to use the different propagation speeds of ultrasound in media with different concentrations, that is, there is a mathematical relationship between propagation time and concentration. The measurement of carbon dioxide concentration is converted into time measurement. In the carbon dioxide concentration measurement channel, the ultrasonic sensor transmitter and receiver are placed on both sides. The transmitter sends a fixed pulse at intervals. The measurement system starts the timer at the same time. The pulse signal passes through the carbon dioxide gas to be measured in the channel. The pulse signal is transmitted to the receiver, and the timer stops immediately. The main advantages of the ultrasonic time difference method for measuring carbon dioxide concentration are good stability and simple operation, but the measurement accuracy is related to the accuracy of the timer. The frequency measurement method or period measurement method commonly used by ordinary timers often have pulse counting errors and response speed problems. Although high-precision timers can reduce counting errors, this will increase additional device costs. Summary of the invention

[0003] The purpose of the present invention is to provide a quantitative compensation time difference measurement method for carbon dioxide concentration, which utilizes the periodic phase relationship between a fixed frequency pulse signal and an adjustable frequency pulse signal to perform phase discrimination on the phase difference between the signals, and forms a full cycle phase discrimination voltage series within the timing time, thereby realizing high-precision carbon dioxide concentration measurement. The present invention observes the phase discrimination voltage series formed by the phase difference change between the fixed frequency pulse signal and the adjustable frequency pulse signal, so as to quickly adjust the frequency value of the adjustable frequency pulse signal within the timing time, thereby greatly eliminating the counting error of ±1 pulse. The present invention utilizes the physical characteristics of the phase change between pulse signals, has high measurement accuracy, simple circuit structure, and is easy to implement, thereby solving the problems of ±1 pulse counting error and response speed existing in the background technology.

[0004] The technical solution of the present invention is: A quantitative compensation time difference measurement method for carbon dioxide concentration comprises the following steps: ①According to the frequency value of the ultrasonic signal, the measurement system outputs a fixed frequency pulse signal with the same frequency valuef 1. The measurement system outputs an adjustable frequency pulse signal with a small frequency difference relationship with the frequency value of the ultrasonic signal f 2.

[0005] In the measurement system of the present invention, the frequency value of the fixed frequency pulse signal is f 1. The frequency value of the adjustable frequency pulse signal is f 2. During the measurement of carbon dioxide concentration, the ultrasonic sensor transmits a signal at regular intervals. Timing starts when the ultrasonic sensor transmits a signal, and stops when the ultrasonic sensor on the other side receives the signal. The common frequency measurement method or period measurement method can only synchronize the timing start signal with the timing frequency signal, but cannot synchronize the stop signal with the timing frequency signal, which results in a pulse counting error. For example, Figure 1 As shown, in the common frequency measurement method or period measurement method, only t a Start timing and adjustable frequency pulse signal f 2, and then starts counting the adjustable frequency pulse signal. The timing stops when the ultrasonic signal is transmitted to the receiving end of the ultrasonic sensor on the other side through the carbon dioxide gas. t b To stop the timing, t b With adjustable frequency pulse signal f 2 is not synchronized, that is, t a arrive t b In this time switch, the frequency pulse signal can be adjusted f 2 is not a full cycle. The present invention is to solve the problem of stopping the timing when the ultrasonic signal passes through a carbon dioxide gas of unknown concentration. t b With adjustable frequency pulse signal f 2's rising edge.

[0006] During the measurement process of the present invention, the measurement system outputs a fixed frequency pulse signal with the same frequency value as the ultrasonic signal. f 1 and adjustable frequency pulse signal with slight frequency difference f 2. For example Figure 1 As shown, in this case, the phase relationship between the two pulse signals changes regularly, that is, the phase difference between the two pulse signals φ is a monotonically changing period. Assuming the pulse signal f 1 and f 2. Use the rising edge to compare the phase and start timing. t a , fixed frequency pulse signal f1 and adjustable frequency pulse signal f 2 is the initial moment, at which the two pulse signals coincide with each other. After that, the phase difference generated by the rising edge phase comparison of the two pulse signals is △ φ 1, △ φ 2, △ φ 3, △ φ 4. After a period of transmission time, the ultrasonic signal reaches the other side at t b The carbon dioxide concentration can be measured continuously, that is t b is the starting time of a new measurement cycle, such as Figure 1 As shown, t c is the stop time of the new measurement cycle. During this timing time, the phase difference between the two pulse signals still follows △ φ 1, △ φ 2, △ φ 3, △ φ 4 changes.

[0007] The present invention utilizes the phase difference characteristic of the periodic change of the carbon dioxide concentration during the continuous timing time to overcome the counting error of the pulse signal, complete the high-precision time difference measurement, and provide a high-precision guarantee for the mathematical relationship between the time difference and the carbon dioxide concentration.

[0008] ②Use pulse phase detector to generate fixed frequency pulse signal f 1 and adjustable frequency pulse signal f The phase difference between 2.

[0009] ③Fixed frequency pulse signal through voltage conversion f 1 and adjustable frequency pulse signal f The phase difference between the two is converted into a phase-comparison voltage.

[0010] The present invention utilizes the physical characteristics of phase comparison between pulse signals to convert the changing phase difference information into voltage information. The converted voltage value presents a periodic variation characteristic, such as Figure 1 In U 1, U 2, U 3. U 4. It is also beneficial for the measurement system to store and observe the information series of this change, so as to prepare for quantitative compensation.

[0011] ④ During the timing time, observe the changes in the phase-comparison voltage, perform quantitative compensation according to the changes in the phase-comparison voltage series, and adjust the adjustable frequency pulse signal f The frequency value of 2.

[0012] like Figure 1 As shown, in actual measurement,t a Start timing and fixed frequency pulse signal f 1 and adjustable frequency pulse signal f 2 rising edge synchronously, but t b Stop timing and adjustable frequency pulse signal f 2 is not synchronized, and is prone to advance or lag. The present invention fine-tunes the pulse signal f 2, the phase difference between the pulse signals changes sparsely, but the physical characteristics of stable periodic changes do not change. In this way, during the timing time, t a arrive t b , t b arrive t c It is the phase-comparison voltage series that changes in a full cycle.

[0013] The characteristic of the present invention is that when the timing time cannot be changed, a stable phase-comparison voltage is first formed, and then the frequency value is adjusted so that the whole cycle phase-comparison voltage sequence is filled within the timing time. t b Stop timing and adjustable frequency pulse signal f 2's rising edge.

[0014] ⑤During the timing time, the measurement system responds to the adjustable frequency pulse signal f The value of the 2 count is n , find the time difference t = n / f 2.

[0015] The present invention utilizes the continuous measurement characteristic of carbon dioxide concentration measurement, that is, the ultrasonic signal is transmitted and received at intervals, so that the pulse signal can be adjusted each time the ultrasonic signal is transmitted and received. f 2, and then the measurement system stores and observes the phase-comparison voltage during the timing time to judge the regulation effect.

[0016] The present invention utilizes the periodic variation characteristics of the phase difference between pulse signals and the periodic variation characteristics of the phase-comparison voltage to quickly compensate and adjust the pulse signal. f 2 frequency value, such as Figure 1 As shown, when t a arrive t b No rapid appearance within the timing period U 1, U 2, U 3.U 4. Assume that only U 1, U 2, U 3. According to the historical change data of the phase-comparison voltage series, determine U 4 and pulse signal f 2 frequency value compensation value △ f , so that the pulse signal is adjusted f The frequency value of 2 can be quickly compensated and adjusted, and then the whole cycle phase-comparison voltage series can be quickly obtained within the timing time. It is precisely because of the quantization of the phase-comparison voltage series that the rapid frequency value compensation adjustment can be achieved.

[0017] The main innovation of the present invention is to convert the phase difference signal which changes steadily into a phase-comparison voltage series, and adjust the pulse signal within the timing time. f 2, forming a full cycle phase-comparison voltage series. At this time, the pulse signal is adjusted f 2. Pulse counting is performed to obtain the time difference. The present invention can have a wide time difference measurement range and can perform high-precision time difference measurement on the changing carbon dioxide concentration.

[0018] The positive effects of the present invention are: the instrument has a simple structure and is easy to implement, and uses a fixed frequency pulse signal f 1 and adjustable frequency pulse signal f 2 phase difference relationship, by storing and observing the stable changing phase-comparison voltage series to quickly compensate and adjust the pulse signal f The frequency value of 2 can greatly eliminate the counting error of ±1 pulse and realize the rapid quantitative compensation time difference measurement of the changing carbon dioxide concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a pulse signal phase detection schematic diagram of the present invention; Figure 2 It is a block diagram of the quantitative compensation time difference measurement system of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below by way of examples. like Figure 2 As shown: The measurement system controls the ultrasonic sensor to transmit and receive signals, and outputs a fixed frequency pulse signal with the same frequency value according to the frequency value of the ultrasonic signal. f 1, and output an adjustable frequency pulse signal with frequency deviation through frequency regulation f 2.

[0021] The measurement system uses a pulse phase detector to measure the fixed frequency pulse signal f 1 with adjustable frequency pulse signal f2. Phase detection, fixed frequency pulse signal through voltage conversion f 1 with adjustable frequency pulse signal f The phase difference between the two is converted into a phase-comparison voltage, and the periodic changes of the phase-comparison voltage series are stored and observed.

[0022] When the phase-comparison voltage sequence of a complete cycle is not formed within the timing time, the measurement system calculates the pulse signal through quantitative compensation. f 2, the frequency compensation value is fed back to the frequency deviation adjustment link to adjust the adjustable frequency pulse signal f 2Make adjustments.

[0023] Through adjustable frequency pulse signal f 2 frequency value adjustment, the measurement system stores and observes the new phase-comparison voltage series during the timing time, and the phase-comparison voltage series and the adjustable frequency pulse signal are f 2, a closed-loop frequency regulation is formed.

[0024] After frequency deviation adjustment, a full cycle phase-comparison voltage is formed within the timing time. The measurement system measures the adjusted pulse signal within this timing time. f 2. Pulse counting is performed to obtain the time difference. This quantitative compensation time difference measurement method greatly eliminates the counting error of ±1 pulse, thereby improving the measurement accuracy.

Claims

1. A quantitative compensation time difference measurement method for carbon dioxide concentration: ①According to the frequency value of the ultrasonic signal, the measurement system outputs a fixed frequency pulse signal with the same frequency value f 1. The measurement system outputs an adjustable frequency pulse signal with a small frequency difference relationship with the frequency value of the ultrasonic signal f 2; ②Use pulse phase detector to generate fixed frequency pulse signal f 1 and adjustable frequency pulse signal f The phase difference between 2; ③Fixed frequency pulse signal through voltage conversion f 1 and adjustable frequency pulse signal f The phase difference between 2 is converted into a phase-comparison voltage; ④ During the timing time, observe the changes in the phase-comparison voltage, perform quantitative compensation according to the changes in the phase-comparison voltage series, and adjust the adjustable frequency pulse signal f The frequency value of 2; ⑤During the timing time, the measurement system responds to the adjustable frequency pulse signal f The value of the 2 count is n , find the time difference t = n / f 2.

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