JPH0312709B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an NMR locking device in a nuclear magnetic resonance apparatus, and particularly to an NMR locking device that can optimally adjust the intensity of high frequency waves irradiated to a sample. .

[Prior art]

In a nuclear magnetic resonance apparatus, the strength of the polarizing static magnetic field must always be maintained at a predetermined value. Therefore, a reference sample is placed in the sample to be measured, and the strength of the magnetic field is adjusted to match the resonance signal of the reference sample. So-called NMR locking is performed to match the peak point.
When performing this NMR locking, in advance,
The level of the high frequency waves irradiated to the sample must be adjusted. If the intensity of the high frequency irradiated to the sample is high, the lock loop system will cause a hunting phenomenon and the resonance signal will also be saturated, resulting in an unstable lock state and damage to the sample being measured.
Adversely affects NMR observations. From the perspective of this hunting phenomenon, it is best to lower the high frequency level irradiated to the sample and the gain of the resonance signal receiver as much as possible, but if you lower the high frequency level, you will have to purposely use the NMR lock signal in a degraded SN ratio. This results in frequent loss of lock. Furthermore, when the high frequency level is lowered, the gain of the receiver must be increased, and the noise level also increases accordingly, so fluctuations in the lock loop system due to this noise cannot be ignored. Therefore, in NMR rocking, it is desirable to set the level of the high frequency irradiated to the sample as high as possible without saturating the resonance signal, and to set the gain of the receiver as small as possible. As a result, in the past, before operating the lock loop, the intensity of the high frequency waves irradiated to the sample was manually changed.
The high frequency level that causes saturation of the resonance signal is detected. However, detecting the high frequency level that causes this saturation and setting the high frequency level to an optimum value are extremely troublesome and troublesome operations.
Furthermore, these operations must be performed each time the sample is replaced, since the high frequency level that causes saturation of the resonance signal varies depending on the type and concentration of the reference sample, the diameter of the sample tube, etc.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an NMR rocking device that can automatically and optimally adjust the intensity level of high frequency waves irradiated onto a sample.

[Structure of the invention]

The NMR rocking device according to the present invention includes a magnetic field generating means, an irradiation coil for irradiating a reference sample in the magnetic field with a high frequency wave, an oscillator for generating a high frequency wave to be supplied to the irradiation coil, and a transmission coil from the oscillator to the irradiation coil. an attenuator for changing the intensity of the high frequency wave supplied; an attenuation rate variable means for changing the attenuation rate of the attenuator so that the intensity of the high frequency wave supplied to the irradiation coil increases with time; means for obtaining a dispersion signal and an absorption signal; a control circuit for locking the strength of the magnetic field at the center of the dispersion signal by controlling the magnetic field generating means based on the dispersion signal;
and a detection circuit that detects saturation of the resonance signal by detecting a breakdown in the proportional relationship between the intensity of the high frequency wave supplied from the attenuator to the irradiation coil and the intensity of the absorption signal, and based on the output signal of the detection circuit. , is characterized in that it is configured to control the attenuation rate variable means of the attenuator.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a magnet device that generates a static magnetic field, and a sample tube 2 containing an observation sample and a locking sample is placed in the generated magnetic field. An irradiation coil 3 is wound around the outside of the sample tube 2, and a high frequency wave oscillated from a high frequency oscillator 4 is transmitted to the irradiation coil by an attenuator 5.
Supplied via. The resonance signal of the lock sample detected by the irradiation coil 3 is amplified by an amplifier 6 and then mixed with the high frequency signal from the oscillator 4 in a first mixer 7 and a second mixer 8. , converted to a DC signal. Here, the phase difference between the two types of high-frequency signals supplied to the first mixer 7 is set to 90 degrees, and a dispersed signal of the resonance signal is obtained from the mixer 7, as shown in FIG. . On the other hand, the phase difference between the two types of high frequency signals supplied to the second mixer 8 is set to 0°,
An absorption signal is obtained from the mixer 8, as shown in FIG. The distributed signal obtained by the first mixer 7 is amplified by a DC amplifier 9 and then sent via a switch 10 to a negative feedback auxiliary coil 11 provided close to the sample tube 2. Supplied. The absorption signal obtained by the second mixer 8 is supplied to a saturation level detector 13 via a DC amplifier 12. The signal from the saturation level detector 13 is supplied to a control circuit 14 which controls the attenuation rate of the attenuator 5.

FIG. 4 shows a specific example of the above-mentioned saturation level detector 13. differential amplifier 1
5, and a sample hold circuit 1 to which the output signal of the first differential amplifier is supplied via a switch 16.
7, a second differential amplifier 18 to which the output signals of the first differential amplifier 15 and the sample-and-hold circuit 17 are supplied, and an output signal of the second differential amplifier;
It is comprised of a comparator 20 that compares the reference voltage from the reference power source 19.

In the configuration as described above, first, switch 1
0 is open, the frequency of the high frequency from the oscillator 4 and the strength of the magnetic field are adjusted so that they substantially satisfy the NMR resonance conditions. Next, in the control circuit 14 of the attenuator 5, a sawtooth wave as shown in FIG. 5 is generated, and the attenuation rate in the attenuator 5 is lowered in proportion to the sawtooth wave. The intensity of the supplied high frequency is increased linearly. As the intensity of the high frequency wave supplied to the irradiation coil 3 increases, the absorption signal of the resonance signal obtained from the second mixer 8 increases in intensity. FIG. 6 shows the intensity A of the high-frequency signal irradiated to the sample and the intensity B of the absorption signal, and when the absorption signal begins to saturate, the amount of change is smaller than the change in the intensity of the high-frequency signal. becomes less,
In a state of supersaturation, the absorption signal strength decreases. The sawtooth signal and the absorption signal are supplied to a saturation level detector 13, and a difference signal between the two signals is obtained in a first differential amplifier 15 in the detector. In the initial state, the switch 16 in the saturation level detector is connected to the sample and hold circuit 17, and the output signal of the first differential amplifier 15 is held in the sample and hold circuit 17. Thereafter, the switch is switched such that the output signal of the first differential amplifier is supplied to the second differential amplifier 18, where the output signal of the first differential amplifier is A difference signal between the signal and the signal held in the sample and hold circuit is obtained. The first
The output signal of the differential amplifier 15 is sent to the attenuator 5.
When the attenuation rate of
The output signal of the second differential amplifier remains unchanged.
The intensity of the high frequency waves irradiated to the sample gradually increases as the attenuation rate of the attenuator 5 decreases, and when the resonance signal starts to saturate, the two types of waves supplied to the first differential amplifier 15 The signal proportionality is broken and the output signal strength of the amplifier 15 becomes greater than the signal strength held in the sample and hold circuit. As a result, the output signal of the second differential amplifier 18 changes as shown by C in FIG.
The output signal of this differential amplifier is sent to a comparator 20
The reference signal from the reference power supply 19 shown as D in FIG. 6 is compared with the reference signal. When the output signal of the second differential amplifier exceeds the reference signal, the comparator 20 generates a signal and sends this signal to the control circuit 14 to fix the attenuation factor of the attenuator 5 at that state. The reference voltage from the reference power supply 19 is preferably 0V, but since the signal supplied to the comparator 20 contains some noise components, it is set to a slightly higher voltage. .

In this way, the attenuation rate of the attenuator 5 is set so that the intensity of the high frequency wave irradiated to the sample is large enough to cause the resonance signal to begin to saturate. After the adjustment of the attenuator 5 is completed, the first
The switch 10 in the negative feedback loop of the NMR lock shown in the figure is closed, and the operation of the negative feedback loop is started. As a result, the magnet device 1 and the coil 11
The magnetic field strength is the center of the dispersion signal shown in Figure 3.
Locked to H ₀ . At this time, the negative feedback loop is
Since the intensity of the high-frequency waves irradiated to the sample is optimally high, the gain of the resonance signal receiving system can be lowered and stable NMR locking can be performed. Although the operation of the negative feedback loop is performed after the adjustment of the high frequency intensity is completed, the adjustment of the high frequency intensity may be performed with the switch 10 closed and the negative feedback loop operating. .

〔effect〕

As detailed above, the present invention provides stable
The intensity level of the high frequency waves irradiated to the sample, which is essential for NMR rocking, can be adjusted automatically and easily. Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, the detector for the saturation level of the resonance signal is not limited to the circuit shown in FIG. Further, although the attenuation rate of the attenuator is controlled by a sawtooth wave, it is not necessary to change the attenuation rate linearly. Furthermore, although not shown, the opening and closing of each switch is automatically performed by a control means such as a computer.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a dispersion signal of a resonance signal, FIG. 3 is a diagram showing an absorption signal of a resonance signal, and FIG. 4 is an example of the embodiment of FIG. 1. Figure 5 is a diagram showing a sawtooth wave, and Figure 6 is a diagram showing changes in the intensity of the high frequency wave irradiated to the sample and changes in the intensity of the absorption signal. be. 1... Magnet device, 2... Sample tube, 3... Irradiation coil, 4... Oscillator, 5... Attenuator, 6,
9, 12...Amplifier, 7, 8...Mixer, 13
...Saturation level detector, 14...Control circuit, 1
5, 18... differential amplifier, 17... sample hold circuit, 20... comparator.

Claims (1)

[Claims] 1. A magnetic field generating means, an irradiation coil for irradiating a reference sample in the magnetic field with high frequency waves, an oscillator for generating high frequency waves to be supplied to the irradiation coils, and a magnetic field generator for generating high frequency waves to be supplied to the irradiation coils. an attenuator for changing the intensity of the high frequency wave supplied to the irradiation coil; an attenuation rate variable means for changing the attenuation rate of the attenuator so that the intensity of the high frequency wave supplied to the irradiation coil increases with time; and a dispersion signal of the resonance signal of the reference sample. a control circuit for locking the strength of the magnetic field at the center of the dispersion signal by controlling the magnetic field generating means based on the dispersion signal; and a control circuit for locking the strength of the magnetic field at the center of the dispersion signal; a detection circuit that detects the saturation of the resonance signal by detecting a break in the proportional relationship between the intensity of the high frequency wave and the intensity of the absorption signal, and the attenuation rate of the attenuator is variable based on the output signal of the detection circuit. an NMR locking device configured to control the means; 2. The detection circuit for detecting the saturation of the resonance signal includes a first differential amplifier whose input terminals are supplied with a signal A corresponding to the intensity of the high frequency supplied from the attenuator to the irradiation coil and an absorption signal B. , the first
a hold circuit that holds the output signal of the differential amplifier at a predetermined time, and a second differential amplifier whose input terminals are supplied with the output signal of the first differential amplifier and the signal held by the hold circuit. and a comparator for comparing the output signal of the second differential amplifier with a reference value.
NMR rocking device.