SU1213383A1 - Digital viscometer - Google Patents

Abstract

The invention relates to a digital viscometer comprising a probe, a cuvette for the substance to be examined, a twisting spring, a cuvette drive, and a measuring circuit based on a resistive sensor. To improve speed, measurement accuracy and noise immunity, a voltage integrator, a voltage comparison circuit based on differential amplifiers, a set of fixed resistors and their connector are introduced into the measuring circuit. One output of the resistive sensor is connected to the non-inverting input of the voltage integrator, and through. the switch and the resistors to the ground lead, and the other through a resistor to the inverter inverter input voltage and to the output of the voltage comparison circuit, one output of which is connected to the integrator output, and the second one to the ground bus, 2 Il. i (L C ND CO 00 00 00

Description

f

The invention relates to the measurement of the rheological characteristics of liquids and pastes, in particular in the manufacture of thick-film micro-circuits, and can be used in the chemical industry.

The aim of the invention is to improve the speed, measurement accuracy and noise immunity of the measurement process.

Figure 1 shows a functionally pneumatic device diagram; figure 2 - timing charts of work in the corresponding points of the circuit of figure 1.

The device contains a stepping motor 1, gears 2, cuvette 3, probe 4, resistive sensor 5, rotating torque shaft 6, twisting spring 7, resistor 8, capacitor 9, f (direct current amplifiers H and 11, block 12 a set of resistor 13 voltage on resistors, a switch 14, a voltage-frequency converter 15, a source of 16 constant voltage and a digital frequency meter 17 ..

Rotor stepper motor

Gear drive related

with a cuvette 3 driven into rotation At one end of the shaft b a probe 4 is fixed, placed in the cuvette 3, and at the other end a twisting spring 7, the other end of which is rigidly connected to the housing. The movable contact of the resistive sensor 5 is rigidly connected to the shaft 6 and electrically connected to the integrator input based on the DC coupler 10 and the output of the comparison circuit based on the DC amplifier 1 connected to the input of the digital frequency meter 17, Second resistive sensor contact 5 is connected directly to the non-rotating input terminal of the 10 DC power supply and through the transfer unit 14 and alternately connected resistors in block 12 of the set of resistors to the ground bus.

Non-inverting amplifier input

An II current is connected to the integrator output, and the ground that inverts the bus. The input of the voltage-frequency converter (FLL) 15 is connected via a switch 14 to a voltage divider 13 fed by a DC power source. lirioK

832

The stepper motor control is not shown in FIG.

The device works in the following way,

The cuvette from the electric drive is driven into rotation, and due to the presence of frictional forces between the particles in the sample under study, the shaft 6 is twisted, increasing in proportion to the moment

twisting the output resistance Rf of the resistive sensor.

The shear rate V in the sample under study is changed discretely by switch 4, which connects the FPU input

15 with the output of the divider 13 voltage on the resistors cd. At the same time, the corresponding value of the frequency is set on the b) - course of the FNC 15, and the stepping motor rotates at a speed

proportional to a given frequency. Simultaneously, the switch 14 switches the corresponding resistor R, 1 in block 12 with the inverting input of the DC amplifier 10

At the same time, between the values of the resistors RA in the divider 13 and the resistors Ry in the block 12, the dependence should be directly proportional, i.e.

 A to.

where K, | coefficient of proportionality.

The angular velocity of rotation of the cell depends on the frequency of the FNC 15 and, accordingly, on the voltage removed from the voltage divider 13 on the Poison resistors. Then we have

cJ К „Р; d, where К - conversion factor

 n is the resistor Id to the angular velocity of rotation of the cuvette. Taking into account that CA,) tanp V, where f is the angle of inclination of the generatrix of the probe cone., The shear rate in

the sample of pasta we get:

d. tan, p, „-„ j

  K K

I x. I v o

(one)

Devices on the basis of 10 and 11 DC amplifiers

50 runs in the generator for the first y l lx pulses.

The resistors R / j-U R. are injected as a divider of the output voltage - ± Uo comparison circuit on DCF 11.

55 Consider the operation of the device at times t (O), t (O and t (O +), (Fig2). In 1 "ment t (when the output voltage U 0 at the inputs

312i

UPT 10 a and cG present in-phase: signal

Uc

:: /

(j ij

  Cg RV

(2)

(the common mode signal at the inputs of the differential TFC is not amplified). At time t (0), the comparison circuit 11 is triggered, and a potential is set at the input S of the integrator

1, Uo Ry

 Rfvrv

which is transmitted in jumps to the output of the FPD 10, and then through the capacitor C to the input of the integrator iSH so that the potential difference at the inputs from and at the time of the jump is:,. (. ", .2У, .5, .. R.

as a result of the large imbalance at the input of the UFT 10, the output voltage of the integrator continues to increase abruptly, reducing, by means of negative feedback through capacitor C, the imbalance at the input. When reaching the equality + U + Ua, the output voltage of the integrator

/ „Uo RV will be (2.)

Ka

From the moment t. (O) the capacitor of the integrator begins to discharge under the action of the feedback voltage from the output of the DCF 1 1 and in time t (time tj) the output voltage of the integrator will reach zero. Then the comparison scheme, and. the described process will begin to repeat,

The frequency of the generated pulses is determined from the equation iUo - T 2Uo RV. /..h RC () T RV

Substituted (2) and (W), and shaft (1), and also that

Rf - Cs L,

where r is the radius of the probe cone;

ЕЗ is the coefficient for converting the angle of rotation to resistance;

I shear stress when

3

get the following expression for the output frequency of the device pulses

g J-B1 aCg KAKGKL. to; T 4RCR k RC tan V

-j where 4 --p- - viscosity, i.e. the frequency of the pulses from the output of the UFT 11 is directly proportional in the area of the test substance. Frequency is measured by frequency meter 17 to obtain a digital readout in units of dynamic viscosity.

Claims (1)

Invention Formula A digital viscometer containing a measuring probe mounted on one end of the shaft, a cuvette with a test sample of a substance, a twisting spring, an electric actuator and a resistive sensor of the spring torque, and the second 5, the end of the shaft is connected to the housing through a twisting spring, and the cuvette in which the probe is placed is equipped with a drive, so that, in order to increase Q speed, measurement accuracy and noise immunity, a voltage integrator and a voltage comparison circuit based on DC differential amplifiers, a set of constant resistors according to the number of required rotation speeds of the cell, and a resistor switch, are introduced. the springs are connected directly to the non-inverting input of the voltage integrator and through a switch and alternately connected resistors in the resistor block to the ground bus, and The other is via a resistor to the inverting input of the voltage integrator and to the output of the voltage comparison circuit, one of the two inputs of which is connected to the output of the voltage integrator via a capacitor with the inverting input of the voltage integrator, and the second with a ground voltage. five 0 Phi.1