SU1337731A1 - Position pickup of microviscosimeter rotor - Google Patents

Abstract

The invention relates to the field of instrumentation and can be used for measuring the viscosity of dilute solutions of biopolymers and other liquids. The purpose of the invention is to increase the sensitivity of the sensor and eliminate the effect of temperature change on its readings. Setting the phase shifter to the maximum of the useful signal allows you to suppress the effect of temperature changes on the resistance of the coils. 1 il. DO with

Description

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The invention relates to instrumentation and can be applied to measure the viscosity of dilute solutions of biopolymers and other liquids.

The purpose of the invention is to increase the sensitivity of the sensor and eliminate the effect of temperature changes on its readings,

The drawing shows a diagram of the device.

The device contains identical coils 1 and 2 located directly above and below the working volume symmetrically relative to the rotor 3 of a cylindrical shape with a core of ferromagnetic material. Coils 1 and 2 together with capacitors 4 and 5 form two parallel identical series resonant circuits. The common point a is grounded through a small active resistance 6 and is connected to the direct input of the linear amplifier 7. The output of the amplifier 7 is connected to the middle point b of the primary winding of the current transformer 8. The secondary winding is connected to the input of the narrowband amplifier 9, the output of which is connected to the signal input phase detector 10, the reference input of the detector is connected to point b through phase shifter 11, which serves to adjust the phase detector 10 to a maximum of the useful signal and fully suppress the signal caused by the temperature gradient to carcases 1 and 2,

The system works as follows.

When the rotor 3 is located symmetrically with respect to coils 1 and 2, the jet bridge composed of coils 1 and 2 of capacitors 4 and 5 is in equilibrium. The resonant frequencies of its branches coincide. The gain in the loop amplifier 7 is an ab bridge that is large enough. Oscillations occur in the loop, the frequency of which is determined by the overall resonant characteristic of the bridge between points a and b. If the amplifier 7 has an internal automatic gain control, the amplitude of the oscillations at point b can be stabilized at any level. Due to the resonance and symmetry of the circuit, the currents in both parts of the bridge are equal in amplitude and coincide in veil with the voltage at point b. With full symmetry

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The magnetizing effect of the currents in both parts of the primary winding of the current transformer 8 is compensated, and there is no signal on the secondary winding,

Assume that the rotor 3 has moved vertically upwards. The inductance of coil 1 increases slightly, and the inductance of coil 2 decreases, respectively, the resonant frequency of the first circuit decreases, and the frequency of the second circuit increases. The overall resonant frequency of the bridge between points a and b remains almost unchanged. Consequently, the frequency and amplitude of the generator at point b do not change. With a slight shift of the rotor 8, the amplitude of the current in the individual branches of the bridge varies little, its phase varies greatly. The sign of the phase shift depends on the direction of the rotor 3 displacement. Therefore, a constant signal is generated at the output of the detector 10 proportional to the magnitude of the rotor shift, and its sign is determined by the direction of this shift. Despite the small size of the rotor 3 and small changes in the inductance of coils 1 and 2, the sensitivity of the system is quite high due to the use of resonance.

Similar changes in the temperature of coils 1 and 2 do not cause spurious signals, since the symmetry of the circuit is not violated. The symmetry is broken only when a temperature difference occurs in coils 1 and 2. In this case, the resonant frequencies of the individual circuits relative to the circuits of the bridge ab do not change. The quality factor varies and becomes different. In this case, the phase of the currents of the branches does not change, their amplitudes become different. Adjusting the detection phase allows you to suppress the effect of temperature changes on the resistance of the coils.

Claims (1)

Invention Formula A microviscometer rotor position sensor, containing a generator in the form of a linear amplifier with two coils with a feedback circuit, is located symmetrically with respect to the rotor along the vertical axis, in order to increase the sensitivity of the sensor and eliminate the effect of temperature on its display, The feedback circuit is made in the form of a resonant bridge of two identical parallel circuits composed of series-connected coils and capacitors, which are connected to the halves of the first hydrochloric current transformer, the secondary winding of which is connected to the signal input of synchronous detector whose reference input through a phase shifter connected to the output of the linear amplifier. D  f Compiled by V. Voshchankin. Editor L. Pcholinsk. Tehred L. Serdyukova Corrector. Roshko Order 4121/39 Circulation 776 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4