Absorption detector for nuclear magnetic resonance measurements with a frequency control

Claim 1

An absorption detector for determining nuclear magnetic resonance with automatic frequency control, said detector comprising a sample holder including coils, a reference osCillator including a tank circuit coupled to said coils, a magnet including modulating coils and power coils and having a gap in which said holder is positioned; said refeence oscillator including a low-noise amplifier, a resistor, and a limtter connected in feedback rlation with said amplifier via said resistor; a low-frequency amplifier, a synchronous detector coupled via said low-frequency amplifier to said reference oscillator, an XY recorder coupled to said synchronous detector, a modulating oscillator coupled to said modulating coils, reference oscillator and synchronous detector, power supply means coupled to said power coils and to said XY recorder to determine the X position of the latter, and automatic control means coupled to said reference oscillator to control the frequency thereof; said automatic control means includng a crystal oscillator, a mixer coupled to said crystal oscillator and to said reference oscillator and beating the signals thereof, and a rate meter coupling said mixer to said low-noise amplifier; said detector further comprising a source of a reference voltage, a source of stabilized voltage, a switch coupled to said sources, and means coupled to said switch for selectively comparing the rate meter output with the reference voltage to generate an error signal which is fed to said low-noise amplifier and to provide for a magnetic sweep.