JPH0713626B2 - Magnetic oximeter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic oximeter that detects the oxygen gas concentration in a measurement gas by utilizing the magnetic properties of oxygen gas.

<Prior Art> A magnetic oximeter is an analyzer that measures the oxygen concentration in a measurement gas by utilizing this property, because the magnetic susceptibility of oxygen gas is much larger than that of other gases. The applicant of the present application is Japanese Patent Application No. 60-
We proposed a unique magnetic oximeter shown in Fig. 5 by 161601.

In the figure, a part 1 surrounded by a one-dot chain line is a detection part, and 2 is a conversion part. SC is a measurement cell housed in the detection unit 1, of which
101 is a closed loop measurement passage forming a measurement chamber, 102 and 103 are inlets and outlets for the measurement gas Sg provided at symmetrical positions of the measurement passage 101, and 104 is provided at an intermediate portion between the inlet 102 and the outlet 103. A bypass pipe that connects the two arc-shaped measurement passage portions, and 105 is an inlet for the purge gas Pg provided at the center of the bypass pipe. Also, bypass pipe 104 and measurement passage 101
A magnetic field (Mf) forming means using, for example, a permanent magnet is provided at one of the connecting portions A and B of the connecting portions A and B.

Reference numerals 106 and 107 denote purge gas inlets 105 in the bypass pipe 104.
A temperature-measuring resistance sensor for detecting a purge gas flow, which is provided in a symmetrical position with a large temperature coefficient of resistance such as a thermistor.

In the conversion unit 2, 201 and 202 are temperature control circuits connected to the sensors 106 and 107, respectively, and 203 is a subtraction circuit that takes the difference between these outputs. The temperature control circuits 201 and 202 are circuits that control the temperature of the sensors 106 and 107 to be constant in order to eliminate the delay in the thermal response of the sensors 106 and 107.

With such a configuration, when the measurement gas Sg does not contain oxygen gas, the oxygen gas is not sucked into the magnetic field Mf, so the purge gas Q _L diverted toward the connection portions A and B in the bypass pipe 104. , change in the flow rate Q _R is not. On the other hand, when the measurement gas Sg contains oxygen gas, the suction of oxygen gas to the magnetic field Mf occurs, and the flow of oxygen gas at the arrow Q _O occurs, and as a result, the flow velocity of Q _L decreases and Q _R The flow rate of

The change in the flow velocity of the purge gases Q _L and Q _R diverting the bypass pipe 104 corresponds to the oxygen concentration in the measurement gas Sg, which is detected from the change in the resistance value of the temperature measuring resistance sensors 106 and 107. The resistance values of these sensors change according to the flow rates of the purge gases Q _L and Q _R , but feedback is applied from the temperature control circuits 201 and 202 to change the power supply voltage of the sensors 106 and 107, and the temperature of these sensors, that is, the resistance value is constant. Controlled to be.

The magnitude of these feedback signals, the purge gas Q _L, corresponds to the flow rate of Q _R, the output signal V _R of the temperature control circuit 201 is given to the subtraction circuit 203 as V _L, these differences in the circuit And is output as an output signal V _O.

In the case of such an apparatus, the sensors 106 and 107 are the purge gas Q _L ,
Since Q _R is placed in the pipe flowing constantly, there is the advantage that a large detection output signal component is obtained, further, subtraction circuit
Since the difference between the detection outputs of the sensors 106 and 107 is taken by 203, there is a strong advantage against external impact or vibration.

<Problems to be Solved by the Invention> However, the detection outputs of the sensors 106 and 107 and the purge gas Q
_L, is in the non-linear relationship between the flow rate of Q _R (flow rate), the purge gas Q _L, when the flow rate of Q _R has changed, by simply just took the difference between the detection output of the sensor 106 and 107 pull the measurement error Wake up.

Further, when the measurement gas Sg contains H ₂ and He gases, these gases have a larger diffusion coefficient than other gases, and the bypass pipe 1 is provided against the outflow of the purge gas Pg from the connection portions A and B.
04 Enter inside. Due to such gas diffusion, a temperature distribution is generated in the bypass pipe 104, which has a thermal effect on the sensors 106 and 107 and causes an output error.

The first technical problem to be solved in the present invention is
In the above-mentioned magnetic oxygen, it is to prevent the influence of the non-linear characteristic of the sensor from appearing in the detection result.
The technical problem of (1) is to prevent the influence of a gas component having a large diffusion coefficient contained in the measurement gas.

<Means for Solving the Problems> In the configuration of the first invention of the present invention, a measurement gas inlet and an outlet are provided at symmetrical positions of a closed loop measurement passage, and a bypass pipe is provided at an intermediate position between these inlet and outlet. And a measuring chamber having a purge gas inlet at the center of the bypass pipe, a magnetic field forming means provided at one of the connecting portions of the bypass pipe and the closed loop measurement passage, and the purge gas inlet being symmetrical. A detection unit including a pair of temperature-measuring resistance sensors for purge gas flow detection provided in a position and arranged in the bypass pipe, and output from the pair of sensors and the purge gas when the flow rate of the purge gas is zero. V _O = K performs subtraction correction of the zero error takes in the output from said pair of sensors in a state ^{_{{V R -V RO) 1/2 -}} (V L -V LO) 1/2} where, V _R : Non magnetic field Sensor detection output V _RO: purge flow detection output V of the non-magnetic side sensor when zero _L: detection output V _LO magnetic field side of the sensor: the detection output of the magnetic field of the sensor when the purge gas flow rate is zero K: a constant value, and a conversion unit configured to output a signal in which the influence of the non-linear relation is removed based on the equation, and the configuration of the second invention of the present invention is a closed loop measurement passage. A measurement gas inlet and an outlet are provided at symmetrical positions, a bypass pipe is connected to an intermediate position between the inlet and the outlet, and a purge gas introduction port is provided in the center of the bypass pipe, the bypass pipe and the closed loop. Field forming means provided on one side of the connection portion of the shape measuring passage, a pair of throttles arranged symmetrically across the purge gas introduction port and arranged in the bypass pipe, and this throttle and the purge gas introduction port are sandwiched. And a detection unit comprising a temperature measuring resistance sensor for purge gas flow detection provided at symmetrical positions, the output from the pair of sensors when the flow rate of the purge gas is zero, and the pair of sensors when the purge gas is flowing. _{V O = K {V R -V} RO) 1/2 - (V L -V LO) 1/2} performs subtraction correction of the zero error takes in the output of the proviso, V _R: the non-magnetic side sensor Detection output V _RO : Detection output of non-magnetic field side sensor when purge gas flow rate is zero _VL : Detection output of magnetic field side sensor V _LO : Detection output of magnetic field side sensor when purge gas flow rate is zero K: Constant And a conversion unit including a calculation unit that outputs a signal in which the influence of the non-linear relation is removed based on the equation (1).

<Operation> The first aspect of the present invention operates as follows. That is, first, the zero error signal detected by the pair of sensors is stored when the purge gas flow rate is zero, and then the detection is performed with the purge gas flowing, and the zero error signal is subtracted from the detection signal. , Get a zero compensated signal output.

The non-linear relationship between the purge gas flow rate and the detection signal of the sensor is known in advance, a non-linear correction calculation is performed based on this non-linear relational expression, and the difference between these non-linearly corrected signals is taken to obtain the sensor An oxygen gas concentration signal that is not affected by nonlinear characteristics is obtained.

In addition to the operation of the first invention, the second invention operates as follows. That is, the gas with a large diffusion coefficient contained in the measurement gas has an exponential concentration distribution from the connection portion with the closed loop measurement passage toward the sensor, and the concentration of the diffusion gas in the sensor portion is the purge gas. The higher the flow velocity of, the lower.

In the present invention, a pair of throttles are provided across the purge gas introduction port to increase the flow velocity of the purge gas to reduce the concentration of the diffusion gas in the sensor portion so that the influence of the composition of the measurement gas does not appear in the measurement result. I have to.

<Example> An example of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the apparatus of the present invention.
FIG. 2 shows a measuring cell in an apparatus of the present invention, FIG. 2A is a plan view thereof, and FIG. 2B is a CDE in FIG.
FIG. In these figures, elements that are substantially the same as the elements in FIG. 5 are assigned the same reference numerals and explanations thereof are omitted. First, in FIG. 1, the detection unit 1 is a thermostatic chamber, and the measurement gas Sg is supplied to the measurement cell SC through the filter 108 and the diaphragm 109. Purge gas Pg is a filter
It is given to the measuring cell SC through 110 and the capillary 111. 11
2 is a magnet for generating a magnetic field, 113 is a detection circuit, 114 is a temperature detection element, and 115 is a heater.

The measuring cell SC portion will be described in detail with reference to FIG.
The measuring cell SC consists of two parts, an outer ring 116 and an inner disc 117. The ring-shaped measuring passage 101 forming a closed loop is formed by sealing a groove provided on the outer periphery of the disk 117 with a ring 116. Measuring gas Sg
The inlet 102 and the outlet 103 are provided on the upper surface of the disk 117 so as to be inside the ring-shaped measurement passage 101. The magnet 112 is embedded in the disk 117. Reference numerals 118 and 119 are throttles provided at symmetrical positions in the bypass pipe 104 with the purge gas introduction port 105 interposed therebetween.

Returning to FIG. 1, in the conversion unit 2, 204 is a multiplexer, and the output of the detection circuit 113 selected here is converted into a digital amount by the A / D conversion circuit 205, and the input / output port 206
Then, it is taken in by the microprocessor 207. on the other hand,
The signal detected by the temperature detection element 114 is also detected by the detection circuit 113, A / D
It is taken into the microprocessor 207 via the conversion circuit 205 and the input / output port 206, and a temperature control signal is given to the heater drive circuit 208 to drive the heater 115 to control the temperature. In addition, 209 is a ROM in which a calculation program is stored, 210
Is a display / key unit, and 211 is an output circuit.

Next, the operation of the apparatus thus configured will be described. First, prior to the measurement, detection is performed by the sensors 106 and 107 while the purge gas Pg is zero, and the detection output at this time is stored in the microprocessor 206 as a zero error signal. Then, the purge gas Pg is flowed to perform the measurement,
The zero error signal is subtracted from the detection signal detected at that time to perform zero correction.

The flow rate of the purge gas Pg and the detection outputs of the sensors 106 and 107 have a non-linear relationship, and the relationship is known in advance. For example, when the detection signal has a squared characteristic as shown in FIG. 3 with respect to the purge gas flow rate, V _O = K {(V _R −V _RO ) ^1/2 − (V _L −V _LO ) ^1/2 } (1) is calculated to obtain the oxygen gas concentration output V _O that is not affected by the nonlinear characteristics of the sensors 106 and 107.

(However, V _L : detection output of the magnetic field side sensor 106, V _R : detection output of the non-magnetic field side sensor 107, V _LO : magnetic field side sensor 106 when the purge gas flow rate is zero
Detection output, V _RO : detection output of the sensor 107 on the non-magnetic field side when the purge gas flow rate is zero, K: constant) On the other hand, when the measurement gas Sg contains H ₂ and He gas with a large diffusion coefficient, These diffusion gases enter the bypass pipe 104 against the outflow of the purge gas Pg from the connection portions A and B. This diffusion gas has an exponential concentration distribution from the connecting portions A and B toward the sensors 106 and 107, and has a concentration C _N (X) in the sensor 106 and 107 portions as shown by the following equation.

C _N (X) = C _NO · exp {− (V · X) / Dn} (2) (where C _NO : concentration of diffusion gas at connecting portion A or B, V: flow velocity of purge gas Pg, X : From connection A, B to sensor 1
(Distance to 06,107, Dn: Diffusion coefficient of diffusion gas) As can be seen from this equation, if the flow velocity V of the purge gas Pg is increased or the distance X from the connecting portions A and B to the sensors 106 and 107 is lengthened, diffusion will occur. The ratio of will decrease exponentially.

As a method of lengthening X, a method of linearly lengthening the bypass pipe 104 cannot be adopted because the entire cell SC becomes large. The bypass pipe 104 may be formed in an inverted S-shape or S-shape as shown in FIG. 4 to increase the pipe length.
In the case of such a method, there is a drawback that the conduit resistance increases and the processing becomes difficult.

On the other hand, as a method of increasing V, a method of increasing the flow rate of the purge gas Pg can be considered, but it is not a good idea to expedite the consumption of the purge gas.

In the present invention, the purge gas inlet 105 is sandwiched between the pair of throttles 1
18,119 are provided, and the flow velocity of the purge gas is increased at these throttles to reduce the influence of the diffusion gas.

<Effect of the Invention> According to the first invention of the present invention, in the above-described magnetic oximeter, the influence of the non-linear characteristic of the sensor does not appear in the detection result. Further, according to the second aspect of the present invention, in addition to the effects described above, the influence of the diffusion gas contained in the measurement gas does not appear in the detection result.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the device of the present invention, FIG. 2 shows a measuring cell in the device of the present invention, FIG. (A) is a plan view thereof, and FIG. (B) is a sectional view thereof. 3 and 4 are explanatory views for explaining the apparatus of the present invention, and FIG. 5 is a block diagram of a conventional apparatus. 1: detection part, 2: conversion part, 101: measurement passage, 102: measurement gas inlet, 103: measurement gas outlet, 104: bypass pipe, 105: purge gas inlet, 106, 107: sensor, 112: magnet, 113: Detection circuit, 118, 119: Aperture, SC: Measuring cell, Mf: Magnetic field, Sg: Measuring gas, Pg: Purge gas, A, B ... Connection part

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-51-144295 (JP, A) JP-A-53-12674 (JP, A) JP-A-64-6753 (JP, A) JP-A-47- 1250 (JP, A) Japanese Patent Publication No. Sho 49-10280 (JP, B1) US Patent 3471776 (US, A) US Patent 3302448 (US, A)

Claims (2)

[Claims] 1. A measurement gas inlet and an outlet are provided at symmetrical positions of a closed loop measurement passage, a bypass pipe is connected to an intermediate position between the inlet and the outlet, and a purge gas inlet is provided at the center of the bypass pipe. A measurement chamber, a magnetic field forming means provided at one of the connecting portions of the bypass pipe and the closed loop-shaped measurement passage, and a pair of purge gas flows disposed in the bypass pipe at symmetrical positions with respect to the purge gas inlet. A detection unit consisting of a temperature measuring resistance sensor for detection, the output from the pair of sensors when the flow rate of the purge gas is zero and the output from the pair of sensors when the purge gas is flowing are taken in to subtract a zero error. A magnetic oximeter comprising: a conversion unit configured to perform correction and output a signal in which the influence of a non-linear relationship is removed based on the following equation. V _O = K {(V _R −V _RO ) ^1/2 − (V _L −V _LO ) ^1/2 } where V _R : Detection output of the non-magnetic field side sensor V _RO : When the purge gas flow rate is zero Detection output of non-magnetic field side sensor V _L : Detection output of magnetic field side sensor V _LO : Detection output of magnetic field side sensor when purge gas flow rate is zero K: Constant 2. A measuring gas inlet and an outlet are provided at symmetrical positions of a closed loop measuring passage, a bypass pipe is connected to an intermediate position between the inlet and the outlet, and a purge gas introducing port is provided at the center of the bypass pipe. A measurement chamber, a magnetic field forming means provided at one of the connecting portions of the bypass pipe and the closed loop-shaped measurement passage, and a pair of throttles provided at symmetrical positions across the purge gas introduction port and arranged in the bypass pipe. , A detection unit composed of a temperature measuring resistance sensor for purge gas flow detection, which is provided at a symmetrical position with the throttle gas and the purge gas introduction port interposed therebetween, and outputs from the pair of sensors and the purge gas when the flow rate of the purge gas is zero. The output from the pair of sensors in the state of flowing the current is taken in to perform the subtraction correction of the zero error, and the influence of the non-linear relation is removed based on the following formula. Magnetic oxygen analyzer comprising a conversion unit comprising a calculation means for outputting a signal. Serial _{V O = K {(V R} -V RO) 1/2 - (V L -V LO) 1/2} where, V _R: detection output V _RO of the non-magnetic side sensor: When the purge gas flow rate is zero Output of non-magnetic field side sensor of V _L : Detection output of magnetic field side sensor V _LO : Detection output of magnetic field side sensor when purge gas flow rate is zero K: Constant