Densitometer

Claim 2

A vibration densitometer comprising: a probe having a structure adapted to be vibrated at its resonant frequency; first means actuable to vibrate said structure; second means to produce an alternating output signal at the output thereof a frequency the same as that at which said structure is vibrating; a tracking filter having a signal input, a signal output and a control input; third means connecting the output of said second means to the signal input of said tracking filter; an oscillator having an output connected to said third means in a manner to add an auxiliary alternating electrical input signal to said tracking filter input in addition to that supplied by said third means responsive to said second means output signal; a phase comparator having first and second inputs and an output; a control for said tracking filter connected from said comparator output to said tracking filter control input to vary the location of the pass band of said filter in accordance with the magnitude of the signal appearing at said comparator output, said tracking filter signal input and signal output being connected to said comparator first and second inputs, respectively; and fourth means connected from said tracking filter signal output to said first means to actuate said first means to vibrate said structure at the frequency of the signal appearing at the signal output of said tracking filter.

Claim 3

A vibration densitometer comprising: a probe having a structure adapted to be vibrated at its resonant frequency; first means actuable to vibrate said structure; second means to produce an alternating output signal at the output thereof a frequency the same as that at which said structure is vibrating; a tracking filter having a signal input, a signal output and a control input; third means connecting the output of said second means to the signal input of said tracking filter; an oscillator having an output connected to said third means in a manner to add an auxiliary alternating electrical input signal to said tracking filter input in addition to that supplied by said third means responsive to said second means output signal; a phase comparator having first and second inputs and an output; a control for said tracking filter connected from said comparator output to said tracking filter control input to vary the location of the pass band of said filter in accordance with the magnitude of the signal appearing at said comparator output, said tracking filter signal input and signal output being connected to said comparator first and second inputs, respectively; and fourth means connected from said tracking filter signal output to said first means to actuate said first means to vibrate said structure at the frequency of the signal appearing at the signal output of said tracking filter.

Claim 4

A vibration densitometer comprising: a probe having a structure adapted to be vibrated at its resonant frequency; first means actuable to vibrate said structure; second means to produce an alternating output signal at the output thereof a frequency the same as that at which said structure is vibrating; a tracking filter having a signal input, a signal output and a control input; third means connecting the output of said second means to the signal input of said tracking filter; an oscillator having an output connected to said third means in a manner to add an auxiliary alternating electrical input signal to said tracking filter input in addition to that supplied by said third means responsive to said second means output signal; a phase comparator having first and second inputs and an output; a control for said tracking filter connected from said comparator output to said tracking filter control input to vary the location of the pass band of said filter in accordance with the magnitude of the signal appearing at said comparator output, said tracking filter signal input and signal output being connected to said comparator first and second inputs, respectively; and fourth means connected from said tracking filter signal output to said first means to actuate said first means to vibrate said structure at the frequency of the signal appearing at the signal output of said tracking filter.

Claim 5

The invention as defined in claim 1, including utilization means connected from said tracking filter signal output.

Claim 6

The invention as defined in claim 1, wherein said third means includes a differentiator and a squarer connected in that order from said second means to the signal input of said tracking filter, said squarer having an input and an output, said differentiator having an output connected to said squarer input, said oscillator also having its output connected to said squarer input.

Claim 7

The invention as defined in claim 3, wherein said tracking filter includes fifth and sixth means to provide a lower and higher limits, respectively, to the excursion of said pass band thereof, said oscillator being constructed to have an output signal frequency equal to that midway between said limits, said oscillator being constructed to have an output signal amplitude less than that of the output signal of said differentiator when said oscillator output is disconnected from said squarer input and said structure is immersed in a fluid and vibrated at a resonant frequency, f, given by f Square Root A/d - B where, d is the density of said fluid, A is a constant, and B is a constant, said fifth and sixth means including first and second resistors, respectively, said tracking filter including a center junction, first and second capacitors, third and fourth resistors and a first amplifier having first and second inputs and an output, said first amplifier input being grounded, said third resistor being connected from said squarer output to said center junction, said second capacitor being connected from said center junction to said first amplifier first input, said fourth resistor being connected from said first amplifier output to said first amplifier first input, said first capacitor being connected from said first amplifier output to said center junction, said fourth means being connected from said center junction, said first resistor being connected from said center junction to ground, said filter frequency control including a second amplifier, fifth and sixth resistors, a third capacitor, a field effect transistor having a source, a drain and a gate, said second amplifier having first and second inputs and an output, said second amplifier second input being grounded, said fifth resistor being connected from said comparator output to said second amplifier first input, said second resistor being connected from said center junction to said transistor drain, said sixth resistor being connected from said second amplifier output to said second amplifier first input, said third capacitor being connected in parallel with said sixth resistor, said second amplifier output being connected to said transistor gate, said transistor source being grounded, said third resistor being connected from said center junction to said first comparator input, said second comparator input being connected from said center junction.

Claim 8

The invention as defined in claim 3, wherein said tracking filter includes means to prevent movement of the pass band thereof beyond upper and lower limiting frequencies, said oscillator having an output signal frequency midway between said limiting frequencies.

Claim 9

The invention as defined in claim 3, wherein said oscillator has an output signal amplitude less than that of a predetermined frequency having the greatest amplitude appearing at the output of said differentiator when said structure is vibrating at its resonant frequency

Claim 10

The invention as defined in claim 6, wherein said tracking filter includes means to prevent movement of the pass band thereof beyond upper and lower limiting frequencies, said oscillator having an output signal frequency midway between said limiting frequencies.

Claim 11

The invention as defined in claim 1, wherein said tracking filter includes means to prevent movement of the pass band thereof beyond upper and lower limiting frequencies, said oscillator having an output signal frequency midway between said limiting frequencies.

Claim 12

The invention as defined in claim 8, wherein said oscillator introduces a signal to said tracking filter of an amplitude less than that of the signal introduced thereto of the resonant frequency of said structure when said structure in vibrating at said resonant frequency.

Claim 13

The invention as defined in claim 1, wherein said oscillator introduces a signal to said tracking filter of an amplitude less than that of the signal introduced thereto of the resonant frequency of said structure when said structure is vibrating at said resonant frequency.

Claim 14

The invention as defined in claim 1, wherein said tracking filter has means to prevent the pass band thereof from falling below a predetermined frequency, said oscillator having an output signal frequency greater than said predetermined frequency.

Claim 15

The invention as defined in claim 1, wherein said tracking filter has means to prevent the pass band thereof from rising above a predetermined frequency, said oscillator having an output signal frequency less than said predetermined frequency.