Densitometer

A vibration densitometer comprising:

• a probe including a vibratable member;
• electrical means actuable to impart vibration to said member;
• pick-up means to produce a first signal in synchronism with said member vibration;
• a loop circuit connected from said pick-up means to said electrical means to form an electromechanical oscillator;
• means connected from said loop circuit to produce a utility signal which is a known function of the density of the fluid in which said member is immersed, said loop circuit including a phase lock loop, said phase lock loop including a phase detector having first and second inputs, an output, a voltage controlled oscillator (VCO) having an input and an output, a resistor connected from said phase detector output to said VCO input, a capacitor connected from said VCO input to ground, a unijunction transistor having a gate connected from said VCO input, said VCO output being connected to said phase detector second input;
• an input circuit connected from said pick-up means to said phase detector first input;
• and an output circuit connected from said VCO output to said electrical means.