JPS6062052A - Medical mass spectrometer - Google Patents

Abstract

PURPOSE:To enable stable analysis to be performed for a long period of time by interchangeably using plural heaters under proper conditions by connecting a power supply circuit to an auxiliary heater when the current level of the heater exceeds a set level. CONSTITUTION:The current output of a heater power supply 6-1 is controlled by the output of a control-voltage-producing circuit. The current level of the power supply 6-1 is converted into a voltage signal by means of a current-detecting circuit 6-3. Next, the voltage signal is compared with a level set in a reference- voltage-producing circuit 6-2 to deliver a voltage output when the voltage signal exceeds the set level. The thus delivered voltage output is then received by a pulse converter 6-5 which converts the voltage output into a step-like pulse which is then delivered from the pulse converter 6-5. Thus produced pulses are accumulated in a counter 6-6 and the pulse level corresponding to the heater that should be selected is delivered to a decorder 6-7 to achieve the changeover of a switch group 6-8 for selecting heaters. By thus measuring the current level of the heater and connecting the power supply circuit to an auxiliary heater when the above current level exceeds a set level, it is possible to perform stable measurement for a long period of time.

Description

[Detailed description of the invention] [Technical field of invention] This invention relates to a medical mass spectrometer.

[Technical background of the invention and its problems]

In recent years, there has been an increasing need to measure oxygen consumption and carbon dioxide production in the fields of pulmonary function testing and patient supervision. In order to perform these measurements, it is essential to measure the oxygen and carbon dioxide concentrations in the breathing gas, and mass spectrometers are excellent for this measurement.

However, mass spectrometers have problems in that they are complicated to handle and have poor maintainability. Particularly problematic are thermoelectron emission heaters, which are treated as consumables. The amount of thermionic emissions from the heater changes over time and decreases, making it impossible to perform gas analysis with sufficient accuracy. Therefore, in order to suppress temporal changes in output, conventional mass spectrometers detect the output, noise ratio, or effective amount of thermionic emission caused by direct gas ionization, and use these values to suppress temporal changes in output. The heater current is equipped with a mechanism for controlling the heater current. Therefore, as the heater becomes fatigued over time and the amount of thermionic radiation decreases, the heater current tends to increase. If the current exceeds a certain value, the fatigue of the heater reaches its limit, and it becomes impossible to continue measurements. Replacing the heater usually breaks the vacuum in the analysis tube, so handling it is naturally complicated. Therefore, I would like to avoid replacing the heater as much as possible.
The ion source of a conventional mass spectrometer is equipped with a plurality of heaters, and uses an external switch to switch to a spare heater when the main heater is disconnected.

However, just before the heater burns out, the amount of thermionic emissions decreases rapidly, resulting in a loss of output reliability, and data collection becomes impossible after the heater burns out.

[Purpose of the invention]

An object of the present invention is to provide a medical mass spectrometer that can perform stable measurements over a long period of time by replacing a plurality of heaters under appropriate conditions.

[Summary of the invention]

In the present invention, the value of the heater current is measured, and when the value exceeds a set value, the power supply circuit is switched to the standby heater.

[Effects of the Invention] According to the present invention, the maximum value of the heater current is determined, the heater power source is protected, and the non-measurement time before and after the heater burnout is significantly reduced, making stable measurement possible over a long period of time. . In other words, when controlling the heater power supply depending on the signal-to-noise ratio, etc., when the heater is extremely fatigued, an excessive current flows through the heater and the heater power supply becomes overloaded, but the heater current exceeds the set value. However, by switching to a new heater, the thermionic emission efficiency increases, and the control mechanism reduces the heater current and protects the power supply.

-1゜In addition, since the heater is replaced before the breaking point, the device does not operate in an unstable state of thermionic emission just before the wire breaks, or in a state where measurements cannot be made after the wire breaks, and this eliminates the need for long periods of time. Stable measurements are performed.

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. FIG. 1 shows a block diagram of a 90 degree magnetic field deflection type medical mass spectrometer. The breathing gas is introduced via the inlet tube (1) through the pulp (2) into the ion chamber (5) in the analysis tube (4) by means of the p1 capillary (3). On the other hand, the heater (7) is heated by the current supplied by the heater power source (6), and thermoelectrons are emitted and guided to the ion chamber (5). This causes thermionic valence collisions in the ion chamber (5), and the breathing gas is ionized. Each gas molecule of nitrogen (Nz) + oxygen (OtL) and carbon dioxide (co, 3) contained in the ionized breathing gas is ionized by the ion gun (9) by the voltage supplied by the ion accelerating power source (8). accelerated, magnetic) 41tl
) enters a magnetic field consisting of

・Each molecule that has been turned on is deflected by this magnetic field according to its mass number, and each collector 11-+ t 11-2 +
11-s. In this example, N2,02 respectively.
．． It is a CO□ channel. The collected ions are transferred to each amplifier (12-+ + 12-2112-3
) is amplified by the voltage VN proportional to each gas concentration.
2. Vo2. Outputs Vco2.

As each output waveform is continuously measured, the amount of ionized molecules gradually decreases due to a decrease in the amount of thermionic emission due to deterioration of the heater, and the waveform changes to a waveform with noticeable noise. At this time, the output voltage of the collector is
) and a low-pass filter (14) are added. The bypass filter (I3) depicts only the noise signal and is added to the amplitude detection circuits α.

The divider circuit e receives the output of the low-pass filter U·υ and the amplitude detection circuit receives the highest output, calculates the signal-to-noise ratio, and outputs the signal-to-noise ratio. This value is given to the comparator circuit (11) and compared with the signal-to-noise ratio setting circuit (a value set from 1 to 1).The output of the comparator circuit (I7) is given to the control voltage generation circuit Sumitomo,
Control its output. That is, if the foil number noise ratio is lower than the initial value, the heater power source is controlled so that the current of the heater (7) increases.

FIG. 2 shows a block diagram inside the heater power supply. The current output of the heater power source (6-1) is controlled by the output of the control voltage generating circuit U@.

This current value is converted into stain voltage a by the current detection circuit (6-3), and compared with the value set in the reference voltage generation circuit (6-3) by the comparison circuit (6-4). Outputs voltage if it exceeds the set value. A pulse converter (6-5) receives this output, converts it into a step-like pulse, and outputs it. A counter (6-6) accumulates these pulses and outputs a value corresponding to the heater to be switched to a decoder (6-7) to switch a group of switches (6-8) for selecting the heater.

Also, in order to avoid the waste of having to reselect the heater when turning off and turning on the power to the mass spectrometer (6-6),
A memory (6-9) that stores the state of the counter is connected to a power source (6-10) that drives the memory when the power is cut off.

In this way, the present invention measures the heater current value and switches the power supply circuit to the standby heater when the value exceeds the set value, making it possible to perform four stable measurements over a long period of time. be.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a detailed block diagram of a heater power source of the embodiment. 1...Introduction tube 15...Amplitude detection circuit 4...
-Analysis tube 19...Control voltage generation circuit 5...Ion chamber 6-2...Reference voltage generation circuit 6...Heater power supply 6-3...Pacific current detection circuit 7...Heater 6
-6...Counter 11...Collector 6-8...
Switch Group Agent Patent Attorney Kensuke Chika (and 1 other person)

Claims (1)

[Scope of Claims] An ion chamber into which gas is introduced, a heater power source for ionizing the gas introduced into the ion chamber, and means for detecting the value of the heater current supplied from the heater power source. means for comparing the value of the heater current with a predetermined reference value; 4? means for supplying switching heater current to the heater; Medical mass spectrometer.