SU1693547A1 - Method for determination of milk fatness - Google Patents

Abstract

The invention relates to a measurement technique and is intended to determine the milk fat content by a thermal method. The purpose of the invention is to improve accuracy. Milk preheated to 90 ° C is placed in an environment in which a constant temperature not lower than 60 ° C is maintained, the cooling time of milk is measured to a temperature not lower than the medium temperature, and the milk fat content is determined by the measured time value . 3 il.

Description

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The invention relates to a measurement technique and is intended to determine the fat content of milk by the thermal method.

The aim of the invention is to improve the accuracy of measuring the fat content of milk.

This goal is achieved by the fact that the preheated to 90 ° C milk is cooled in an environment with a temperature of 60 ° C and the time of its cooling is measured. the value of which determines the fat content of milk.

In the temperature range from 60 to 90 ° C, the heat capacity of milk depends only on the content of fat in it and practically does not depend on temperature. The heat capacity can be determined by heating the milk from the temperature ti to ta (60 ° C Ј ti t2 90 ° C) and measuring the heating time in accordance with the expression

ABOUT)

where Ср - heat capacity of milk;

M is the mass of milk;

a - the heat transfer coefficient of the glass with milk to the environment (to the bath with a temperature of 60 ° C);

F is the heat transfer surface of the glass;

Q is the heating rate.

From expression (1) it can be seen that the heating time depends not only on the heat capacity Cp, but also on the heating rate (power of the heater).

If we measure the cooling time of milk with the same parameters, the heat capacity can be determined in accordance with the expression:

ABOUT

you soot

4 vj

Goh. (2)

As can be seen from (2). hangs only on Cp (i.e. on milk fat content) with unchanged M, a, F and Af t2-ti.

Figure 1 shows the block diagram of the device; FIG. 2 is a graph of temperature versus time during device operation; on fig.Z - calibration graph of the dependence of milk fat N (%) from Gokhldl first measuring cup.,

The device contains a thermostat 1 with a temperature of 60 ° C, a cylindrical metal cup 2 with milk 3, a coaxial metal electrode in the form of a tube 4, a resistance thermometer 5, a bridge 6, an amplifier 7. a comparator 8 at 90 ° C, a comparator 9 at 65 ° C, RS flip-flop 10, high-frequency controlled voltage generator 11, inverter 12, AND 13 logic element, 14 cycles counter, 15 cycles indicator, reference frequency generator 16, pulse counter 17, pulse indicator 18 (time), key 19 for manual or auto start.

The device works as follows.

When the milk temperature is below 65 ° C, the start key 19 through the trigger 10 turns on the generator 11 and starts heating the milk in glass 2, the resistance thermometer 5 changes its resistance and bridge 6, going through the equilibrium position, gives a signal to the comparator 9 at 65 ° C, which, although permitting the passage of pulses from 16, but the inverse output of the RS flip-flop 10 does not permit the passage of pulses from 16 to 17 and t8 until the milk in glass 2 is heated to 90 ° C. When the temperature reaches 90 ° C, the comparator 8 is triggered, the trigger U is juxtaposed to the O state, and by the inverse output of the trigger 10 logical 1 enables counting pulses from 16 to 17, 18 and the cooling time r0hl is read. until the comparator 9 at 65 ° C prohibits the counting of pulses.

The cooling process lasts up to a temperature of 65 ° C. to improve the accuracy of the record and final determination of milk fat content, since

cooling the milk to an ambient temperature of 60 ° C in a thermostat, the process can last for a very long time, which leads to a decrease in measurement accuracy (Fig. 2).

Thus, when the temperature reaches 65 ° C, the comparator 9 prohibits the passage of pulses to the 13,17, 18 counting circuit and on the indicator 18 the number of pulses corresponds to the time cooled G0xl. and definitely

associated with milk fat.

The mode of repeated measurement of milk fat content is carried out by key 19, while the trigger trigger 10 when the temperature drops below 65 ° C turns on the generator

11 and the cycle is repeated, and the number of cycles is read by a cycle counter.

For the implementation of the method, two samples of aluminum cylindrical glasses were made, the first of which is

, 005 m and height, 010 m, and the second with, 020 m and, 040 m, both wall thick, 005 m.

After heating the milk sample in glasses to 90 ° C, the time of cooling the glasses with milk from 90 to 65 ° is fixed at the installation with milk fat content, 5%. and this time was 21.1 s for the first cup, and 250.5 s for the second cup.

Accordingly, the total cooling time (transient) of glasses from 90 to 60 ° C, recorded in the experiments, is 30 s for the first glass and 30 s for the second glass.

Based on the processing of the measurement results, the basic error is about 0.6%.

Claims (1)

Invention Formula A method for determining milk fat content by measuring the time it takes to change its thermal state in the range-temperature of 60-90 ° C, which involves heating the milk, characterized in that, in order to increase accuracy, the heated milk is placed in a cooling medium with a temperature below the milk heating temperature. , and the determination of milk fat content is carried out on the basis of the measured value of its cooling time. gh-in with about FIG. g 16 18 20 22 Time cooling Fig.Z T with