CN101874735A - Multiparameter compensation method for calculating carbon dioxide concentration - Google Patents

Abstract

The invention belongs to the field of bioengineering, and relates to a multiparameter compensation method for calculating carbon dioxide concentration, which comprises the following steps of: establishing a relational graph of thermistor values and infrared sensor values, wherein detection points are actual sensor values measured at different temperatures, and working out a fit curve of thermistor values and actual sensor values; obtaining a temperature compensation offset computational formula, namely delta=a(R'-20)+b(R'2-202)+c(R'3-203) according to the characteristics of the fit curve of the thermistor values and the actual sensor values; acquiring stable data v'f at the reference end during no breath; and when breathing gas flows in a channel, calculating the carbon dioxide concentration after breath attenuation compensation and temperature drift compensation. The multiparameter compensation method can greatly improve the accuracy of a carbon dioxide concentration monitoring system.

Description

A kind of multiparameter compensation method that is used for the carbon dioxide concentration calculation

Technical field

The invention belongs to biomedical engineering field, relate to a kind of carbon dioxide concentration calculation method.

Background technology

The monitoring gas concentration lwevel has great significance on medical and clinical, can reflect patient's O ₂With CO ₂The metabolism situation.

No matter be by-pass flow formula or main stream-type carbon dioxide concentration detector, gas concentration lwevel detection system in the reality is in measuring process, all there is distorted signals to a certain extent, because the fluctuation of infrared light supply and the temperature of detector are floated, and other gases such as oxygen in the mainstream channel, nitrogen dioxide, water vapour, various anesthetic gases can directly have influence on result's output to the factors such as ultrared measurement interference of 4.26 μ m.Therefore need sum up the self adaptation empirical algorithms by experiment, utilize software algorithm that the concentration of system is compensated correction calculation.

Summary of the invention

Main purpose of the present invention is the self adaptation multiparameter compensation method that proposes a kind of data signal that measures according to the real-time continuous of main stream-type carbon dioxide concentration detector.

A kind of multiparameter compensation method that is used for the carbon dioxide concentration calculation, be applied to software compensation to the main stream-type carbon dioxide concentration detector that has main test side and reference edge, main measuring junction and reference edge are close mutually, adopt identical infrared sensor to gather the light intensity signal of different special wavelength lights respectively, by placing critesistor between main measuring junction and the reference edge, comprising as temperature sensor:

(1) set up the graph of a relation of thermosensitive resistance and infrared sensor value, wherein test point is the real sensor value that records under the different temperatures, and makes the matched curve of thermosensitive resistance and real sensor value;

(2) according to the feature of the matched curve of real sensor value and thermosensitive resistance obtain temperature-compensating side-play amount computing formula: Δ=a (R '-20)+b (R ' ²-20 ²)+c (R ' ³-20 ³), R ' is the thermosensitive resistance by the infrared sensor monitoring;

The stable data v ' of reference edge when (3) gathering apnea _f

When (4) in passage, having breathing gas to flow, adopt following method to realize the multiparameter compensation that carbon dioxide concentration is calculated:

(a) gather reference edge signal v in real time _fWith main test side signal v _m

(b) calculate the rate of disintegration at this moment $\mathrm{\η}=\frac{v_f-v_f^{\′}}{v_f^{\′}};$

(c) calculate the signal value v ' utilize the rate of disintegration to compensate main test side to the apnea state _m:

$v_m^{\′}=\frac{v_m}{1-\mathrm{\η}}=\frac{v_m\·v_f^{\′}}{{2v}_f^{\′}-v_f};$

(d) according to the temperature signal of gathering, calculate thermosensitive resistance, and the temperature-compensating side-play amount computing formula that the substitution previous step obtains carries out reverse compensation operation, obtain offset;

(e) according to the deviant that is obtained signal value is compensated, and calculates and will breathe the gas concentration lwevel that obtains behind attenuation compensation and the temperature drift compensation:

$C_{c{o}^2}=k\·\mathrm{Ln}(\frac{v_m}{2v_f^{\′}-v_f}+\mathrm{\Δ})$

K: the constant coefficient during concentration is calculated.

The present invention proposes a kind of self adaptation multiparameter backoff algorithm that is applicable to that carbon dioxide concentration is calculated in the capnometer, taken all factors into consideration the error in data situation that causes by mobile signal attenuation that causes of breathing gas and temperature drift two big factors in the real system, respectively it being carried out adaptive equalization calculates, thereby it is more accurate and valuable to make final analysis obtain the dense carbon dioxide degrees of data, can improve the degree of accuracy of gas concentration lwevel monitoring system greatly.

Description of drawings

The sense channel layout of Fig. 1 main stream-type carbon dioxide concentration measurement device of the present invention.

The circuit structure block diagram of Fig. 2 main stream-type carbon dioxide concentration measurement device of the present invention.

The graph of relation of Fig. 3 temperature-sensitive resistance and infrared sensor value.

Fig. 4 multiparameter compensation method sketch map of the present invention.

The specific embodiment

Gas concentration lwevel multiparameter compensation method of the present invention proposes at the main stream-type carbon dioxide concentration detector, at first provides a kind of detector that backoff algorithm of the present invention is suitable for below.

This kind main stream-type carbon dioxide concentration monitor device infrared light supply 1 and infrared sensor 3 as shown in Figure 1,4 test sides that constitute are vertically opposite, the direction of gas flow is perpendicular in its direction and the gas breathing main channel, main test side and reference edge are set up in parallel on a main respiration channel ancient piece of jade, round, flat and with a hole in its centre, to reach in the process of breathing, in gas flow, detect the purpose of gas concentration lwevel in real time, in order to reduce the error that temperature drift causes, one piece of temperature sensor 5 that is made of critesistor is set in the centre of two test sides, so that collect main test side and reference edge operating temperature data and temperature drift data, be used for carrying out the reverse compensation of temperature drift.

Three metafiltration ripples in light path design, have been used: the light source filter plate 2 that is provided with 3.9 μ m-4.35 μ m at infrared light supply 1 and measurement interchannel; On the measurement passage before main measuring junction and the reference edge, two-layer filter plate is set, ground floor is 7 pairs of measuring junctions of filter plate and the reference edge uniform filtering that adopts 3.9 μ m-4.35 μ m, second layer master measuring junction uses the narrow band filter slice 8 of 4.26 μ m, and second layer reference edge uses the narrow band filter slice 9 of 4 μ m.

The circuit structure block diagram of main stream-type carbon dioxide concentration measurement device is seen Fig. 2.Measuring process is as follows:

The generation of primary signal: the test side that is made of narrow band filter slice and infrared sensor can be converted to the infrared energy variable quantity that detected object absorbs raw electrical signal output.

The pretreatment of primary signal: because primary signal is very faint and have certain interference, so need will collect primary signal amplify, pretreatment such as filtering.

Calculate the gas concentration lwevel value: pretreated signal is carried out digitized processing, make it to be converted to digital signal and be sent to computing unit, the computing unit of present embodiment is high-speed figure processing unit CPU, and CPU analyzes and change and calculate gas concentration lwevel to the data that collect.Computing unit also can adopt computer or other microprocessor.

Consider the concrete condition of the various distortions that mobile signal attenuation that causes of actual breathing gas and sensor temperature drift are caused, according to the analysis to experimental data, the present invention is provided with two compensated part, referring to Fig. 4.

1, breathe attenuation compensation:

Produce photon by light source in the detection system, photon moves on the pick off on opposite and produces the signal of telecommunication.Under the Repiration of reality, because air current flow has percussion to photon, the signal that pick off is accepted can be affected, and signal can be decayed.Different during with apnea when breathing of photon change the signal attenuations that show as on the voltage signal that is reflected to reference edge and main test side after breathing constantly.Therefore, to CO ₂When concentration value calculates, can not directly adopt the value of main measuring junction and reference edge, and should adopt considered to breathe decay and compensate after value.

When in passage, not having air motion, main sense terminals and stable with reference to the sampled signal maintenance of monitoring terminal, and after when in passage, air motion being arranged, the signal that monitors by main monitoring terminal with reference to monitoring terminal is owing to the influence of breathing photon produces decay, suppose that two signals have decay to V2 and V4 respectively, therefore, when the gas concentration lwevel value is calculated, can not directly adopt the value of main measuring junction and reference edge.If the detection path incident intensity is I ₀, the stabilization signal value defined during main sense terminals apnea is v ' _m, and be v ' with reference to the stabilization signal value defined of monitoring terminal _f, because absorption peak does not participate in respiratory at the gas of 4.0 mum wavelengths, so its concentration remains unchanged, the gas flow rate in passage is v, then reference edge signal v simultaneously _fWith main test side signal v _mCan calculate, the rate of disintegration of this moment is

$\mathrm{\η}=\frac{v_f-v_f^{\′}}{v_f^{\′}}$

With main test side signal v _mCompensate to stabilization signal value v ' under the apnea effect according to attenuation rate _mFor:

$v_m^{\′}=\frac{v_m}{1-\mathrm{\η}}=\frac{v_m\·v_f^{\′}}{{2v}_f^{\′}-v_f}$

2, temperature drift compensation:

The gas-monitoring pick off exists certain temperature drift when carrying out signals collecting, under the constant situation of current concentration, if heat up to monitoring device, the signal that detects by the observation temperature sensor changes and can find: when system temperature was raised to r1 by r, the sensor measurement end had small signal drift Δ V _m

Pick off next door is provided with a critesistor and monitors temperature when prepass in main monitoring channel, does the time spent breathing no more, and changes channel temperature, and Fig. 3 provides the relation of thermosensitive resistance and sensor values.The figure mid point is the real sensor value that under the different temperatures same concentration is recorded, and solid line is the matched curve of temperature-sensitive resistance and sensor values.Its polynomial fitting is:

V＝a×R+b×R ²+c×R ³+k

V is the sensor voltage value, and R is a thermosensitive resistance, a, and b, c, k are fitting coefficient.

According to the quantitative drift value of above drift, along with the variation of the temperature acquisition amount of pick off s, the correction that system can be real-time is because the tiny signal skew that variations in temperature is brought, and compensation method is as follows:

Computing unit is according to the temperature signal of gathering, calculate thermosensitive resistance, and adopt above-mentioned polynomial fitting that the signal of sensor end is carried out reverse compensation operation, is the corresponding down signal value of 20K Ω (critesistor value at normal temperatures is 20K Ω) with the monitor value counter-bonification of each thermosensitive resistance to the temperature-sensitive resistance, and the side-play amount formula is:

Δ=a (R '-20)+b (R ' ²-20 ²)+c (R ' ³-20 ³), in the formula, the thermosensitive resistance of R ' for recording by infrared sensor.

At last, with breathing the gas concentration lwevel that obtains behind attenuation compensation and the temperature drift compensation be:

$C_{c{o}^2}=k\·\mathrm{Ln}(\frac{v_m}{2v_f^{\′}-v_f}+\mathrm{\Δ})$

K: the constant coefficient during concentration is calculated.

Claims (1)

1. one kind is used for the multiparameter compensation method that carbon dioxide concentration is calculated, be applied to software compensation to the main stream-type carbon dioxide concentration detector that has main test side and reference edge, main measuring junction and reference edge are close mutually, adopt identical infrared sensor to gather the light intensity signal of different special wavelength lights respectively, by placing critesistor between main measuring junction and the reference edge, comprising as temperature sensor:

(1) set up the graph of a relation of thermosensitive resistance and infrared sensor value, wherein test point is the real sensor value that records under the different temperatures, and makes the matched curve of thermosensitive resistance and real sensor value;

(2) according to the feature of the matched curve of real sensor value and thermosensitive resistance obtain temperature-compensating side-play amount computing formula: Δ=a (R '-20)+b (R ' ²-20 ²)+c (R ' ³-20 ³), R ' is the thermosensitive resistance by the infrared sensor monitoring;

The stable data v ' of reference edge when (3) gathering apnea _f

When (4) in passage, having breathing gas to flow, adopt following method to realize the multiparameter compensation that carbon dioxide concentration is calculated:

(a) gather reference edge signal v in real time _fWith main test side signal v _m

(b) calculate the rate of disintegration at this moment $\mathrm{\η}=\frac{v_f-v_f^{\′}}{v_f^{\′}};$

(c) calculate the signal value v ' utilize the rate of disintegration to compensate main test side to the apnea state _m:

$v_m^{\′}=\frac{v_m}{1-\mathrm{\η}}=\frac{v_m\·v_f^{\′}}{2v_f^{\′}-v_f};$

(d) according to the temperature signal of gathering, calculate thermosensitive resistance, and the temperature-compensating side-play amount computing formula that the substitution previous step obtains carries out reverse compensation operation, obtain offset;

(e) according to the deviant that is obtained signal value is compensated, and calculates and will breathe the gas concentration lwevel that obtains behind attenuation compensation and the temperature drift compensation:

$C_{c{o}^2}=k\·\mathrm{Ln}(\frac{v_m}{2v_f^{\′}-v_f}+\mathrm{\Δ})$ K: the constant coefficient during concentration is calculated.

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