GB2123959A

GB2123959A - Milk abnormality testing aid

Info

Publication number: GB2123959A
Application number: GB08313077A
Authority: GB
Inventors: Ray Vaughan
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-13
Filing date: 1983-05-12
Publication date: 1984-02-08
Also published as: GB8313077D0

Abstract

A device for testing the level of mastitis in milk comprises a conductivity sensor or cell for receiving a milk sample to be tested. The resistance R of the milk sample in the cell is arranged to be compared with the resistance of a resistor R10, the result of the comparison being indicated by red and green LED's D1 and D2. When the milk sample is of higher resistance than the resistor R10, the green LED is energised but when the milk sample is of lower resistance than the resistor R10, then the red LED is energised and the green LED is extinguished. The resistance value of the resistor R10 may be preset at a fixed level or may be arranged to be swept downwardly from high to low values whereby the LED's change over when equivalence of resistance is attained. The variable resistor R10 can be calibrated to enable the corresponding mastitis level to be read off. <IMAGE>

Description

SPECIFICATION Milk abnormality testing aid The present invention is concerned with a device for testing for abnormality in milk and in particular for testing for the level of mastitis in milk.

Of all the causes of abnormal milk in dairy cows, mastitis is unquestionably the most important. Mastitis results in a lowered yield, and milk affected by it produces poor quality milk products which can be dangerous to health because of the large number of pathogens in the milk.

Many forms of mastitis detector have been devised in the past but these have mainly operated on the principle of comparison of the conductivity of the milk under test with a reference sample or a comparison of the conductivities of the milk from different teats of the one cow. There remains a requirement in the industry for a simple to use device which can, in some embodiments, be handheld and which enables immediate quantitative detection and display of the level of mastitis in any milk sample. It is an object of the present invention to provide such a device.

In accordance with one aspect of the present invention, there is provided a device for testing for the level of mastitis in milk, comprising a conductivity sensor adapted to be brought into contact with milk to be tested, a resistance with whose resistance value the resistance of the milk sample is compared by a detection circuit which is adapted to detect whether the resistance value of the milk is greater or less than that of said resistance, and a display means which responds to said detection circuit to indicate visually and/or audibly whether the resistance value of the milk is greater or less than that of said resistance.

The invention also provides a device for testing for the level of mastitis in milk, comprising a conductivity cell for receiving a milk sample to be tested, a variable resistance with whose resistance value the resistance of the milk sample is compared, a trigger circuit adapted to detect equivalence of said resistance values of the milk sample and variable resistance or of a predetermined one of said resistance values just exceeding the other, and a display means which responds to actuation of the trigger circuit to visually and/or audibly identify same.

In accordance with a further aspect of the present invention, there is provided a device for testing for the level of mastitis in milk, comprising: (a) a conductivity cell for receiving a milk sample to be tested; (b) a variable resistance with whose instantaneous resistance value the resistance of the milk sample is compared when the variable resistance is swept through its resistance range; (c) a trigger circuit adapted to detect equivalence of said resistance values of the milk sample and variable resistance or of a predetermined one of said resistance values just exceeding the other; and (d) a display means which responds to actuation of the trigger circuit to visually and/or audibly identify same; (e) the variable resistance being pre-calibrated to enable the corresponding resistance of the milk sample and/or the mastitis level equivalent thereto to be read off.

Preferably, the display means comprises a pair of LED's, one green and one red, arranged so that the green LED is energised as the variable resistance is swept downwards towards lower resistance values until such time as the variable resistance and resistance of the milk sample are substantially the same or one just exceeds the other, whereupon the green LED is extinguished and the red LED is energised. The pre-calibrated mastitis level corresponding to the position then adopted by the variable resistance is read off.

Conveniently, the variable resistance is manually adjusted through its range by means of a rotatable knob positioned on the external surface of a handheld housing containing the conductivity cell. The latter cell is preferably in the form of an open-topped cup disposed on the same surface as the rotatable knob.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a circuit diagram of a first embodiment of a device in accordance with the present invention, which includes an a.c. conductivity bridge; Figure2 is a circuit diagram of a second embodiment of a device in accordance with the present invention, which includes a d.c. conductivity bridge; Figure 3 shows a front perspective view of the preferred housing for a hand-held device in accordance with the invention; Figure 4 shows a further embodiment wherein the conductivity cell is mounted in-line in a milk-carrying vessel; and Figure 5 shows a modification of the embodiment of Figure 4.

All forms of the present device include a conductivity sensor unit. In the case of a hand-held device, the sensor unit can be in the form of an open-topped cup containing one or more pairs of opposed metal electrodes. For example, in the embodiment of Figure 3 there are two pairs of electrodes 10a, lOb and 12a, 12b disposed around the internal periphery of a cup-shaped container or vessel 14. The electrodes in each pair are dosposed 1800 apart. The two pairs of electrodes are connected externally in parallel, as shown in Figure 2, in order to improve the cell efficiency and reliability. The two pairs of electrodes and the container consitute the "conductivity cell" referred to hereinafter.

Such a conductivity cell is indicated in the embodiment of Figure I as being connected between a first pair of terminals A, B. Between a second pair of terminals C, D there is provided a potentometer Rlo designated the "Set-Zero" control. A hex-inverter TC1 is arranged to produce at its terminal E, F a pair of anti-phase, 6KH2 square wave signals which are attenuated by pairs of resistors R4, R5 and R6, R7 and fed by way of respective capacitors C5 and C3, to one side of the set zero control R1O and one side of the conductivity cell, i.e. to terminals C and A, respectively.The other terminals D and B are commonly connected to the non-inverting input of an operational amplifier IC2 having a feedback resistor R12 ("Set sensitivity" control) which sets its gain and hence sets the sensitivity of the circuit. It will be noted that when the effective resistances between the terminals A, B and C, D are equal, then the half-bridge formed thereby is balanced and there is zero signal at the non-inverting input of IC2. However, when these two resistances differ, there is a resultant out-of-balance signal which is amplified by IC2, the phase of the latter signal depending on whether the resistance effective between the terminals CD is greater than that between the terminals AB or vice versa.

The amplified a.c. output of IC2 is coupled to a pair of F.E.Ts TR1 and TR2 which are connected as a synchronous detector 16 coupled to the anti-phase square waves from the hex-inverter IC1. The detector 16 is arranged to produce an output only in response to out-of-balance signals from IC2 of phase indicative of the resistance of the set-zero control R1O being less than that of the milk sample constituting the resistance R between the terminals AB, signals of the opposite phase being ignored by the detector. Thus, if the resistance R1O is initially much higher than the resistance R of the milk then the out of balance signal applied to the amplifier IC2 is of phase F, and this signal is rejected or ignored by the detector 16.

However, as the resistance value of R1O is swept downwards it eventually becomes equal to and then lower than the value R whereupon the phase of the out-of-balance signal changes to that of phase E. The detector 16 responds to this signal and is arranged to produce a d.c. output on line 18. This latter signal is amplified in an amplifier IC4 and applied to a pair of LED's, D1 and D2, D1 is preferably red and D2 is green.

The arrangement of the diodes D1 and D2 is such that when the DC signal is absent on the line 18 then the green diode D2 is turned on and the red diode D1 is turned off but when the signal is present on the line 18 then the green diode is extinguished and the red diode is turned on. This switch-over from green to red thus corresponds to the set-zero resistance R1O having been adjusted to a position where its resistance is just lower than that of the milk sample in the cell.

Amplifier IC3 is used to generate a low-impedance mid-point line voltage on line 20. The connection of the amplifier IC3 to the battery 22 is made via a push-button switch SWAZI in order to conserve battery power.

It will be noted that the illumination equality of the LED's D1, D2 depends on the battery voltage and on the value of a resistor R17 upstream of the amplifier IC3. For a green value of R17, LED D1 will fail to illuminate below a certain battery voltage. Thus, short-circuiting terminals A and B or C and D by means of a switch (not shown) can serve as a battery check.

Referring now to Figure 3, the indicator knob 24 corresponds to the variable "set-zero" control R10 of Figure 1. Alongside the knob 24, the housing is marked with discrete steps corresponding to different positions of the knob 24 and identified as "start", "clean milk free from infection", "subclinical mastitis", "clinical mastitis level A", "mastitis infection level B", and "chronic mastitis levels C.

and D". The positions of these steps around the knob 24 have been determined by prior practical experiment to correspond to the indicated conditions.

Thus, for example, it is known by experimental observation of many hundreds of samples that the resistance R of milk having clinical mastitis, level A is of a certain ohmic value. A fixed resistor at this value is thus placed across terminals A and B and the set-zero resistor varied to the point where the green lamp is switched off and the red light comes on. The position of the indicator knob then corresponds to the clinical mastitis level A condition and the scale on the housing can be marked accordingly. This process is repeated for each condition to build up the complete scale indicated in Figure 3. Then, in practical use of the device, when a particular milk sample has a resistance value corresponding to one of these conditions, this will be identified by the change-over of the coloured diodes when the indicator knob reaches the corresponding position on the scale.

in use, therefore, a milk sample is inserted into the cup containing the electrodes and the knob 24 is turned to its "start" (high resistance) position. The switch SW1 is then closed by depressing a button 28 on the front of the device and the green light comes on. The knob 24 is then turned anti-clockwise through the scale until the red light comes on. The button is then released. The position of the indicator knob on the scale then indicates the relevant level of mastitis in that milk sample. The container is then thoroughly washed out to be ready for a subsequent test.

The embodiment of Figure 2 performs the same task as the embodiment of Figure 1 but is in the form of a simpler, DC arrangement. A UA 741 board is arranged to compare the resistance of milk in the conductivity cell with a variable resistance R1O' equivalent to Rlo of Figure 1. The variable resistance is rotated from its high resistance value until the UA 741 board detects equivalence of the resistance thereof with the resistance of the milk in the cell.

LED's D1' and D2' are then switched over from green to red and the corresponding mastitis condition is read off the scale of the variable resistance in exactly the same manner as before.

Figure 4 and 5 illustrate further embodiments where the sensor is mounted within a milk jar or in-line within milk-carrying pipework with the electrodes 10a, 10b, 12a, 12b in control with the milk flowing through pipework or with the milk present in the jar. The principle of generation is the same as before. An external housing 30 supports the two diodes D1, D2. In the case of the embodiment of Figure 4, the conductivity level at which the diodes changes over is preset internally. In the case of the embodiment of Figure 5, the manually rotatable knob 24 is included to provide (in this case) three different levels at which the device responds by changeover of the diodes D1, D2.

It will be appreciated that the foregoing devices in accordance with the present invention enable a quick convenient and almost instantaneous analysis of mastitis infection levels in individual or bulk milk samples to be carried out.

Claims

1. A device for testing for the level of mastitis in milk, comprising a conductivity sensor adapted to be brought into contact with milk to be tested, a resistance with whose resistance value the resistance of the milk sample is compared by a detection circuit which is adapted to detect whether the resistance value of the milk is greater or less than that of said resistance, and a display means which responds to said detection circuit to indicate visually and/or audibly whether the resistance value of the milk is greater or less than that of said resistance.

2. A device as claimed in claim 1 wherein the display means comprises a pair of LED's arranged so that one LED is energised when the resistance value of the milk is greater than that of said resistance and the other LED is energised when the resistance value of the milk is less than that of said resistance.

3. A device as claimed in claim 2 wherein said one LED is green and said other LED is red.

4. A device as claimed in claim 1,2 or 3 having a housing which is adapted to be hand-held.

5. A device for testing for the level of mastitis in milk, comprising, a conductivity cell for receiving a milk sample to be tested, a variable resistance with whose resistance value the resistance of the milk sample is compared, a trigger circuit adapted to detect equivalence of said resistance values of the milk sample and variable resistance or of a predetermined one of said resistance values just exceeding the other; and a display means which responds to actuation of the trigger circuit to visually and/or audibly identify same.

6. A display device as claimed in claim 5 wherein two anti-phase square wave signals are applied to a common point via the milk sample in the cell and said resistance, respectively, the trigger circuit including a detector adapted to detect the resultant signal at said common point and to trigger the display means accordingly.

7. A display device as claimed in claim 5 or 6 wherein the resistance of the milk sample is arranged to be compared with the instantaneous resistance value of said resistance when the variable resistance is swept through its resistance range, the variable resistance being pre-calibrated to enable the corresponding resistance of the milk sample and/or the mastitis level equivalent thereto to be read off.

8. A device as claimed in claim 7 wherein the display means comprises a pair of LED's arranged so that one LED is energised, as the variable resistance is swept downwards towards lower resistance values, until the variable resistance and the resistance of the milk sample are substantially the same or one just exceeds the other, whereupon said one LED is extinguished and the other LED is energised.

9. A device as claimed in claim 8 wherein said one LED is green and said other LED is red.

10. A device as claimed in any of claims 5 to 9 wherein the variable resistance is manually adjustable through its range by means of a rotatable knob positioned on a housing containing the conductivity cell.

11. A device as claimed in claim 10 wherein the housing is adapted to be hand-held.

12. A device as claimed in any of claims 5 to 11 wherein the conductivity cell comprises an opentopped cup.

13. A device as claimed in claim 12, when appendant to claims 10 or 11 wherein the opentopped cup is contained in the same surface of the housing as said rotatable knob.

14. A device as claimed in any of claims 5 to 11 wherein the conductivity cell is adapted to be mounted within a milk container or in-line within milk-carrying pipework.

15. A device for testing for the level of mastitis in milk, comprising a conductivity cell for receiving a milk sample to be tested, a variable resistance with whose instantaneous resistance value the resistance of the milk sample is compared when the variable resistance is swept through its resistance range, a trigger circuit adapted to detect equivalence of said resistance values of the milk sample and variable resistance or of a predetermined one of said resistance values just exceeding the other, and a display means which responds to actuation of the trigger circuit to visually and/or audibly identify same, the variable resistance being pre-calibrated to enable the corresponding resistance of the milk sample and/or the mastitis level equivalent thereto to be read off.

16. A device for testing for the level of mastitis in milk, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.