WO1983003305A1

WO1983003305A1 - Electrical conductivity device for detecting mastitis in dairy cows

Info

Publication number: WO1983003305A1
Application number: PCT/US1983/000362
Authority: WO
Inventors: Inc. Wescor; Earl Levell Tippetts; George B. Bersonnet
Original assignee: Wescor Inc
Priority date: 1982-03-18
Filing date: 1983-03-16
Publication date: 1983-09-29
Also published as: DE3337020T1; GB2127156B; GB2127156A; GB8328958D0

Abstract

An electrical conductivity testing device for detecting mastitis in dairy cows includes an inlet (56) for receiving a sample of milk to be tested, a conductivity cell (60) having a milk flow-through testing passage (59, 61, 62) in flow communication with the inlet, and a milk discharge outlet (65) in flow communication with the conductivity cell, so that a milk sample enters the inlet, flows through the conductivity cell, and flows out through the discharge outlet. The flow described may be continuous or may be discontinuous so that the sample is held in the conductivity cell at least during taking of the conductivity measurement. The conductivity cell is arranged so that it is completely filled with milk during the taking of conductivity measurements. Electrical circuitry is provided to produce an electrical signal proportional to the conductivity of the milk in the conductivity cell. A preferred embodiment of the device takes conductivity measurements, individually and sequentially, of samples of milk from the four quarters of a cow's udder and produces electrical signals representing respective individual conductivity measurements on a scale of from 0 to 9 by electrical comparison of such conductivity measurements with a reference value (31), preferably by means of a bridge amplifier circuit (16, 31, and 32), and exhibits respective digits representative of such measurements, preferably side-by-side, on a readout screen (25) provided as a part of the instrument.

Description

ELECTRICAL CONDUCTIVITY DEVICE FOR DETECTING MASTITIS IN DAIRY COWS

Technical Field: This invention is in the general field of mastitis detecting devices for use in the dairy industry and is particularly concerned with devices of this type that test electrical conductivity of milk secretions of the mammary glands of dairy cows. Background Art; Various ways of testing dairy cows for the disease known as mastitis, which infects the mammary glands of a great many of the dairy cows being milked throughout the world, have been developed in the past. None of these have been entirely satisfactory. Viscosity testing of milk from each of the four quarters of the udder of a dairy cow is commonly used in the U.S. Testing electrical conductivity of the milk has been tried experimentally in the U.S. and has been used in New Zealand. Infected quarters of an udder produce milk lower in lactose and higher in sodium chloride than quarters of an udder that are not infected, and electrical conductivity of such milk is not the same as that from non-infected quarters. Ordinarily, not all quarters of a dairy cow's udder are infected or infected to the same degree, so that comparing the electrical conductivity of milk taken sequentially from the four quarters provides a reasonably reliable indication of mastitis infection.

A -conductivity test instrument which has achieved significant commercial success in New Zealand, where it was developed, is described in an article entitled "Method of Mastitis Detection Including the Rolling Ball

Viseometer and Electrical Conductivity Meter" by Graham F. Doire appearing on pages 25-34 of the Proceedings of the 19th Annual Meeting of the National

Mastitis Council Inc. held at Louisville, Kentucky, on February 18-20, 1980. It provides for measuring conductivity of milk from the four quarters of a dairy cow's udder individually and in sequence and includes a switching system controlling the energizing of a green and a red light, individually or together, to indicate relatively low, relatively high, and intermediate conductivity measurements, respectively. The four readings are recorded by an observer and compared to establish a positive or negative condition for each quarter. Although this New Zealand device has the advantages of being relatively inexpensive and easily operated by a dairyman at cowside, with more easily and more quickly interpretable results than had been possible theretofore, it requires a second person to be present to record the results of each quarter testing and does not provide adequately for differences in herd type, particular stages of lactation, or individual cow chemistry.

Further, in use, milk is introduced into a closed-bottom conductivity cell, the measurement taken, and then the cell turned upsidedown to empty the milk before another sample of milk is placed in the cell for testing. It has been found with such a device that milk remains on the sides of the cell after the sample is poured out, so that, that after several readings have been taken, the samples become contaminated and the cell has to be cleaned before further use. Ideally, the cell should be cleaned after every use.

In the U.S., where testing has been done regarding the relationship between conductivity readings and the presence of mastitis, the tests have all been experimental using laboratory bench-type conductivity meters. Again, such meters have closed-bottom conductivity cells to hold the samples of milk being tested or prong-like conductivity cells which are inserted into closed-bottom containers holding the samples, and in both cases, the cells and containers must be washed out each time a test is made. Disclosure of the Invention

According to the invention, an electrical conductivity testing device for detecting mastitis in dairy cows includes means, such as a funnel-like receptacle, for receiving a sample of milk to be tested, an electrical conductivity cell having a milk flow-through testing passage in flow communication with the sample receiving means, and milk discharge means in flow communication with the conductivity cell so that a sample enters the receiving means, flows through the conductivity cell, and flows out through the discharge means. Means, such as a loop formation in the testing passage, flow control valve, etc., is provided to ensure that the conductivity cell is completely full of milk when testing electrical conductivity and electrical circuitry is connected to the conductivity ceE for powering such cell and for generating an electrical signal representative of the conductivity of the milk in the cell. The device of the invention may be constructed for use as a hand-held instrument by a dairy farmer at cowside, or for use as a part of laboratory milk-analyzing equipment, or for use in-line with a milking machine to provide continuous information as a cow is being milked.

In one preferred embodiment of the device, conductivity measurements are made of the four quarters of a cow's udder, individually and sequentially, with a hand-held instrument by sequentially passing respective samples of milk through a flow-through conductivity cell of the instrument, and electrical signals representing respective individual conductivity measure¬ ments are obtained on a scale of from 0 to 9 by electrical comparison with a reference value, preferably by means of a bridge amplifier circuit that senses electrical impedance deviations from a known reference impedance, and by exhibiting the measurements on a readout screen provided as a part of the instrument.

The individual measurement values are put into display form on the readout screen by demodulating and amplifying the respective electrical signals from the bridge circuit, by applying them to an analog to digital converter, and by feeding the output of such converter to a display driver. Display digit control is preferably accomplished manually by means of individual electrical switches corresponding to the respective quarters of the udder. Operation of the switches causes a final comparative display of four digits representing the four quarters of the udder being tested.

Thus, this embodiment of the invention provides for a simultaneous, comparative display of conductivity measurements of all four quarters of a cow's udder and responds quickly to procedures easily carried out by a single operator working at cowside. The device can be -manufactured and sold at a price well within the ability of individual diarymen working their own small dairy farms.

In another embodiment of the invention, the conductivity cell is placed in a milk-sample line of milk analyzing equipment, so that conductivity readings are taken on respective milk samples, along with other tests made on such samples. In this embodiment, the conductivity readings are obtained as they are with the hand-held instrument, and signals indicative of the conductivity of the respective samples tsted are supplied to a meter and/or, where appropriate, to a computer, such as a microprocessing unit, in the analyzing equipment. With such analyzing equipment, there is no need for four comparative readings on samples taken from the four quarters of a cow's udder.

fRE A

_, „ 71PO In still another embodiment of the invention, the conductivity cell is placed near the claw of a milking machine, so that conductivity measurements are made of samples of milk as the milk flows through the machine. In some instances, the milk from all four quarters of the cow's udder will be mixed prior to sampling, in which ease a single reading will be taken for each cow being milked, but, in other instances, it will be possible to obtain samples for the respective quarters, in which case, four comparative readings will be obtained.

Principal advantageous effects of the invention are the obtaining of conductivity measurements of milk determinative of mastitis infection on a milk milk flow-through basis; self-cleaning of the conductivity cell as milk samples flow through, so that contamination between samples is avoided without having to wash out the cell after each use; the fact that a bridge amplifier circuit having less than the normal number of components may be used to sense the conductivity of the milk in the cell; and, in the case of the hand-held instrument, the fact that separate readings for each of the four quarters of a cow's udder can be generated and displayed for easy comparison. Brief Description of Drawings In the accompanying drawings, which illustrate an embodiment of the device constituting the best mode presently contemplated of carrying out the invention in actual practice:

Fig. 1 is a front elevational view of the device as it is held by a dairy farmer for testing and for viewing the readout screen; Eig. 2, a top plan view showing where the milk samples are deposited for testing purposes;

Fig. 3, a rear elevational view, with portions of the housing broken away to show otherwise hidden parts;

Fig. 4, a block diagram showing how electrical and electronic equipment are interconnected into operative test and display circuitry;

Fig. 5, a detailed wiring diagram and schematic of the system as a whole;

Fig. 6, an exploded view of a second embodiment of the device of Fig. 1 showing how the conductivity cell may be mounted as a removable insert for ease of replacement; Fig. 7, a rear elevation of the device of Fig. 6 with insert in place and part of the casing broken away to show milk receptacle and the flow path of successive milk samples;

Fig. 8, a horizontal section taken on the line 8-8 of Fig. 6 showing the construction of the electrodes;

Fig. 9, a block diagram showing the invention applied to milk analyzing equipment; and

Fig. 10, a block diagram showing the invention applied, in-line, to milking equipment. Best Modes for Carrying Out the Invention

In the embodiment illustrated in Figs. 1-3, the electrical components are compactly housed within a casing 10, Figs. 1-3, adapted to be held by a hand of a dairyman located by the side of a dairy cow and ready to withdraw milk from the four quarters of the cow's udder sequentially. Casing 10 is preferably injection-molded to shape from a suitable plastic material, such as acrylic butadiene styrene, better known as A.B.S. Its top is open as at 11, Fig. 3, and is formed for receiving and retaining a cap 12, which is also preferably injection molded to shape from a suitable plastic material such as the same acrylic butadiene styrene as the casing 10 on which it fits. Cap 12 is of funnel formation, having an open top portion 12a, Fig. 2, funneling into a depending discharge spout 12b, Fig. 3, serving as a milk reservoir which terminates in a nipple type of connection fitting 12c of considerably reduced diameter. Reservoir 12b provides a receiving means for the sample of milk to be tested. Attached to nipple 12 c is one end of a length 13 of flexible tubing, which serves as an air entrapment device. Its other end is attached to an end of a relatively short length 14 of stainless steel tubing passing through an electrical binding post 15, so as to become one electrode of an electrical conductivity measurement cell identified in general as 16. Such cell 16 is completed by connection of another length 17 of flexible tubing to an end of a second, relatively short length 18 of stainless steel tubing which passes through a second electrical binding post 19 to become the second electrode of such conductivity measurement cell 16.

The other end of stainless steel tubing 18 is connnected to another length 20 of flexible tubing, whose other end is attached to a stainless steel nipple 20a connected to a rigid, discharge tube 21, which is preferably molded integrally with casing 10 and has an open end 21a communicating with the atmosphere through the otherwise closed bottom 10a of easing 10, comprising discharge means for the device.

As a matter of convenience in the use of the device, the rear wall 10b of casing 10 is windowed, as at 22, so as to expose to view from the exterior of the casing conductivity measurement cell 16 and a nine volt, dry cell battery 23, which powers the unit.

The front wall 10 c, Fig. 1, of casing 10 is windowed at 24 to expose a readout screen 25 to view from the exterior of the casing. In the present embodiment, five manually operated, switch push buttons 26 are mounted in front casing wall 10c below readout window 24.

Readout screen 25 is part of an electrical, digital, display device of standard type, such as a Fairehild LTB1042RSX, providing for, in this instance, side-by-side display of four digits, each being one of a series of possible digits from zero to nine as automatically selected according to respective results of sequential tests of milk drawn by the operator from the four quarters of a dairy cow's udder. Thus, the device of the invention provides a comparative readout of the test results on all four quarters of the udder. In using the device, milk is squirted directly from the teat concerned into the funnel top 12a of cap 12. One or two squirts is sufficient. The milk funnels down into reservoir 12b and more slowly from there into and through stainless steel tubing 14, non-conductive, flexible tubing 17, and stainless steel tubing 18 constituting conductivity measurement cell 16. The conductivity measurement is obtained almost instantaneously as the milk sample flows through on its way to discharge tube 21.

While the tubes leading to and from conductivity cell 16, as well as the cell itself, could be straight and either vertically positioned or positioned at an incline, so that milk from reservoir 12b will flow therethrough without stopping and the conductivity measurement taken as the milk flows through the cell, it is preferred that the tubes and cell be arranged in loop fashion, as shown, so that a milk sample will enter the cell and flow therethrough until the inflow milk level in tube 13 is at the level of the top of discharge tube 21 and, thus, fills the tubes and cell therebetween. At this point, the sample remains in the conductivity cell 16 until either a new sample is introduced into the cell to force out and replace the previous sample therein, or until the

^" ΪPO device is tipped in such manner to allow the sample to flow out. In this way, it is easy for a farmer to introduce a milk sample into the device and obtain a reading at his own speed without having to take a reading at the exact time the milk flows through the cell and possibly miss a reading because his timing is not fast enough.

If equilibrium is reached with each sample, so that the sample milk level in tube 13 is equal to the level of the discharge tube 21, each subsequent milk sample will force an air bubble into the conductivity cell in advance of such sample, so as to purge the system of the immediately preceding milk sample. While such bubble between samples is preferred, it is not necessary so long as samples can be introduced into the system without mixing in reservoir 12b. It has been found that the flow-through system described is extremely effective in completely flushing one sample from the system as the next sample is introduced, so that there is substantially no detectable mixing of samples or contamination of the sample as it flows into, through, and out of the celL This avoids the necessity of cleaning the cell after every use, or after every set of several uses, to avoid mixing and contamination from sample to sample as is the ease in cup-type conductivity cells if not washed thoroughly. It is important in order to obtain accurate conductivity readings that the same volume of milk be in the cell each time a reading is taken. For this reason, it is important that the cell be completely full of milk for each conductivity reading taken. In the embodiment of the device shown in Figs. 1-3, this is accomplished by making reservoir 12b of relatively large capacity in comparison with substantially the combined capacities of conductivity cell 16, nipple 12c, and tube 13 leading from reservoir 12c to conductivity cell 16. Thus, conductivity cell 16 has a volume of about 2 ml while a squirt or two of milk into reservoir 12c provides significantly more than that volume and more than encompasses the opening into nipple 12c to insure that milk substantially without air bubbles flows into tubing 13 and into cell 16.

The electrical circuitry presently contemplated as best for this embodiment of the invention is shown generally in block form in Fig. 4. An oscillator 30 supplies an A.C. signal to the conductivity cell 16 of the unit and to a reference resistor 31. The signal passing through the reference resistor is compared to the signal passing through the conductivity cell in comparison circuitry 32, and the output of the comparison circuitry (an A.C. signal proportional to the difference in resistance between the conductivity cell and the reference resistor) is converted to a D.C. analog-difference signal and amplified by demodulator and amplifier 33. The D.C. signal from demodulator and amplifier 33 is fed to an analog to digital converter 34, where such analog- difference signal is converted to a digital signal which is sent to a display driver 35 operating a digital display device 36 adapted to display an appropriate digit in a selected part of readout screen 25.

Switching circuitry 37, Fig. 5, contains five switches, an "on" switch 37 a operated by the appropriately-designated push button 26 a, and four separate switches 37b-37e operated, respectively, by push buttons 26b through 26 e designated for the respective four quarters of a cow's udder.

In operation, "on" switch 37 a is first actuated to supply power to the various components of the circuitry from power supply 38 which includes battery 23. Power supply 38 is connected to all circuitry components, as indicated. After the power is turned on, each of the four quarters are tested in turn by sequentially passing milk therefrom through the conductivity cell and by pushing corresponding test buttons 26b through 26 e.

An automatic off-circuit 40 is provided to turn off the power supply after a preset time period, so that the unit is not accidentally left on when not in use. This prevents the battery from becoming unnecessarily discharged. This auto- off circuit is preferably set to turn off the power supply twenty to thirty seconds after the "on" switch or any one of the test switches is closed. A low battery indicator circuit 41 is preferably provided to give an -indication when the battery becomes discharged and should be replaced.

Variously constructed circuits could be used for each of the blocks described above. However, the circuitry shown in Fig. 5 is the best presently contemplated for use in the device. The individual circuits corresponding to the individual blocks in the diagram of Fig. 4 are marked off by broken lines and correspondingly designated.

As shown, oscillator 30 comprises an astable, multivibrator, integrated circuit ICl, such as a CD4047BE manufactured by RCA. The output of ICl is a square wave, the frequency of which is set by capacitor Cl and resistor Rl. The square wave output of ICl is connected through resistors R2 and R3 to the bases of transistors QI and Q2. Resistors R2 and R3 reduce the voltage from ICl. The square wave from ICl alternately turns on transistors QI and

OMPI Q2, thereby giving a square wave output at terminal 42 between the transistors which is reduced in amplitude to about 2.8 volts rather than the 5 volt amplitude from ICl. The purpose of transistors QI and Q2 is to reduce the source impedance of the oscillator circuit. The reduction in the voltage of the square wave output from five volts to 2.8 volts is to lower the output below the common mode voltage of the amplifier IC2 in the next stage. This prevents overloading of that amplifier.

The square wave signal from terminal 42 is connected through capacitor

C2 to one electrode 16a of conductivity cell 16. The square wave signal is also connected through capacitor C3 to resistor R4, which is the reference resistor heretofore designated 31. Capacitors C2 and C3 block any D.C. component of the square wave signal from the oscillator.

The second electrode 16b of conductivity cell 16 is connected to one input terminal of a differential operational amplifier IC2, such as an ICL 7641 made by Intersil, in comparison circuitry 32. Thus, the signal passing through the milk sample in the conductivity cell is fed to one input of IC2. The signal passing through reference resistor R4 is fed to the other input of IC2. Conductivity cell 16, together with resistor R4, additional resistors R5 and R6, and integrated circuit IC2, form a bridge amplifier network which has two fewer components than a conventional bridge amplifier network and has better impedance characteristics so that bridge loading due to amplifier input resistance is not a factor. The A.C. transfer function of this bridge amplifier network is shown by conventional operational amplifier theory as:

Eo = Rf (R4-RC) Ein RC (R4 + Rf) where R5 and R6 = Rf, and RC is the resistance of the conductivity cell.

With the resistance of resistor R5 equal to that of resistor R6, resistor

R4 establishes a known reference value for comparison with the resistance measured by conductivity cell 16. Thus, the output of IC2 is a square wave, with amplitude proportional to the difference in resistance between the conductivity cell and reference resistance R4.

The output of IG2 is demodulated and amplified in circuit 33. The signal from IC2 passes through capacitor C4 and resistors R7 and R8 and is connected to one input terminal of differential operational amplifier IC3, which is similar to IC2. Transistor Q3 is connected, at 43, between the signal line connecting resistor R7 with R8 and a line 44 carrying a reference voltage of 2.5 volts from the power supply of 38, which is one-half the standard five volt output of such power supply, as explained below. This reference voltage is also connected to the other input terminal IC3. The base of transistor Q3 is connected, through current- limiting resistor R9, to an output of multivibrator ICl, which produces a high, i.e. five volt signal, during the high, i.e. five volt cycle, of the square wave. This high signal turns on transistor Q3 during half a cycle of the square wave and, when the transistor is "on", clamps point 43 to substantially the reference voltage of 2.5 volts. This puts a D.C. component in the square wave signal from IC2 after passing through C4. Capacitor C4 blocks this D.C. component from the comparison circuitry.

Integrated circuit IC3, in conjunction with feedback resistor RIO and capacitor C5, act to filter out the A.C. component of the signal on the input of IC3 and provides output from IC3 that is a D.C. signal biased to 2.5 volts and proportional to the difference in resistance between the resistance of the conductivity ceE and reference resistor R4. Diode Dl is provided to clamp the output of IC3 to a maximum value, so that no number greater than nine will be indicated by the display.

The output of IC3 is connected to the analog input of an analog to digital converter IC4 (box 34), such as an ADC0804 made by National Semiconductor. Since the input to IC4 is limited as described, so that only outputs indicating numbers between zero and nine are obtained from IC4, the outputs of IC4 representing the four most significant bits are used. They are fed into display driver IC5 (box 35), such as a DF411CJ made by Siliconϊx. Rn and C7, as connected to IC4, set the timing of the internal clock, and D2 and C8, also connected to IC4, are provided to insure proper start-up of the internal oscillator.

As previously indicated, power is supplied to the circuitry by a standard nine volt battery 23. The positive terminal of the battery is connected to the ground input terminal of a five volt voltage regulator IC6, such as an LM 320 MP-5.0 made by National Semiconductor. This ground terminal is used as the positive, five volt terminal for the circuitry. The negative terminal of the battery 23 is connected through the automatic shut-off circuitry 40 to the input terminal of regulator IC6. The regulated output terminal from IC6 is used as the ground terminal for the circuitry. Capacitor C9 is a filter

OMPI capacitor for the input to IC6, while capacitor CIO is a filter capacitor for the output from IC6.

The positive terminal of battery 23 is also connected to one side of push button switches 37a though 37e in switching circuit 37. Switch 37a is the power "on" switch controlled by the lowermost push button 26 a. When push button 26a is depressed, switch 37a is closed to thereby connect the positive five volt supply to the parallel combination of resistor R12 and capacitor Cll, and such combination across the terminals of the battery. With switch 37 a closed, capacitor Cll is charged to nine volts. This positive voltage is connected to inverter IC7 through resistor R13. When push button 26a is released, switch 37 a opens and capacitor Cll discharges through resistors R12 and R13. The time constant for the circuit is set so that capacitor Cll remains sufficiently charged to provide a positive input to IC7 for a period of between twenty and thirty seconds. With this positive voltage on the input to inverter IC7, the signal is inverted. It is inverted again by IC8 and again by IC9, so that the output of inverter IC9 is approximately a negative four volts. Resistor R14 is a feedback resistor supplying positive feedback to IC7 to cause the inverters to switch more quickly. The minus four volt signal from IC9 is sent to the input of voltage regulator IC6 in power supply circuit 38 and serves to energize the power supply. When capacitor Cll discharges to the extent that it no longer provides a positive input to IC7, the output of IC9 goes to plus five volts which, in effect, connects the input of IC6 to the plus five volts line which is also the ground connection for IC6. This results in zero voltage potential across IC6 so that no power is supplied to the circuit.

As part of power supply circuit 38, resistors R15 and R16 are connected between plus five volts and ground as a voltage divider. The voltage between resistors R15 and R16 is connected to one input of differential operational amplifier IC10, similar to IC2. The output of IC10 is connected back to its other input as feedback. A filter capacitor C12 is connected in parallel with R16. The output voltage of IC10 is one-half the supply voltage, i.e. 2.5 volts. This is used by comparison circuitry 32 and by demodulator and amplifier circuitry 33 as explained above. Switch 37b is the switch for the left front quarter of the udder. When

37b is closed, the positive voltage is again connected so as to charge

OMPI capacitor Cll and thereby again start the timing cycle of power supply 38. The positive voltage is connected to Cll through diode D3, which prevents any back flow of current from Cll when 37b is open. W^τith 37b closed, positive voltage is also supplied through diode D4 across resistor R17 to display driver IC5 (box 35). This input to the display driver causes the digital number input to the driver from analog to digital converter 34 to be displayed in the extreme left position of the readout screen 25 of display IC11 (box 36). This display will now remain, even when 37b is opened. Display IC11 is preferably a liquid crystal display, such as a Fairchild LTB1042RSX. Switch 37c is the switch for the right front quarter of the udder. When

37c is closed, a positive voltage is supplied through a diode D5 to again charge capacitor Cll, to keep the circuit energized for an additional time period. The positive voltage is also supplied through a diode D6 across a resistor R18 to the terminal of display driver IC5, which causes the number then on the input to the display driver to be displayed in the second from the left position in the display.

Switch 37 d represents the left rear quarter of the udder, and when closed, similarly charges capacitor Cll through a diode D7 and supplies a positive voltage through a diode D8 across a resistor R19 to display driver IC5. This voltage on IC5 causes the number then on the input of IC5 to be displayed in the third from the left position of the readout screen 25 of display IC11, e. box 36.

Switch 37 e represents the right rear quarter of the udder, and, when closed, both charges capacitor Cll through a diode D9 and supplies a positive voltage through a diode D10 across a resistor R20 to display driver IC5. This voltage on IC5 causes the number then on the input to IC5 to be displayed in the fourth position from the left of the readout screen 25 of display IC11.

Thus, if "on" switch 37a is activated by manually pressing its push button 26a and milk from the left front quarter of the udder is squirted into the device and flows into conductivity cell 16 thereof, analog to digital converter IC4 (34) will supply a signal to the four parallel lines connecting IC4 with IC5 (35) representative of a number between zero and nine which is proportional to the difference in resistance between reference resistor 31 and conductivity cell 16. If switch 37b is now closed by pressing its push button 26b, that number will appear in the extreme left position of the readout screen 25 and will remain displayed as long as the power remains on. Push

OMPI button 26b should be pressed only momentarily and then released to open switch 37b again and to hold the number representative of the conductivity of the milk from the left front quarter in the display. It should be noted that push button 26b must be pushed while the milk sample to be measured is in the conductivity cell 16.

With switch 37b open, milk from the right front quarter is squirted into the device. Conductivity of this new sample will be measured and displayed in the second from the left position of readout screen 25 when switch 37c is closed by pressing its push button 26 c If the same procedure is followed for samples of milk from the left rear quarter and right rear quarter of the udder and switches 37 d and 37 e are closed, respectively, the display on- readout screen 25 will show four digits side-by-side, each between zero and nine representing the conductivity measurements for the milk samples from each of the four quarters of the udder. With these side-by-side measurements, it is easy to determine which, if any, of such quarters are infected with mastitis.

As indicated above, milk from a quarter of the udder which is infected with mastitis will be higher in sodium chloride content and lower in lactose content than milk from non-infected quarters. Thus, milk from infected quarters will have a higher conductivity than milk from non-infected quarters. Although with the same herd type differences in particular stages of lactation and individual cow chemistry affect the conductivity of normal milk, it does so only to limited extents. Thus, there is a point at which conductivity above a certain maximum value for a particular herd type indicates mastitis infection. It is preferred that the value of the reference resistor be chosen so that the sensitivity of the comparison circuitry and demodulator and amplifier circuitry be such that any reading on the display of the instrument of "5" or over indicates a conductivity above this maximum and indicates an infected quarter. Thus, any reading obtained for a quarter which is "5" or above indicates mastitis infection. If readings for all quarters are "5" or above, all quarters are infected.

Mastitis can be present even when conductivity of the milk does not reach the maximum leveL In such cases, however, it is very unlikely that all quarters of the udder will be infected. Also, in such cases, the milk from the infected quarter or quarters will be higher in conductivity that milk from the other quarters. Variations of one or two counts in the output of the device is normal between milk from different quarters, but differences of three counts or more indicates that the quarters with the higher counts are infected.

After measurement of conductivity of all four quarters is complete so that four digits representing the conductivity measurements are side-by-side on the display, the user of the instrument can easily determine the lowest reading and differences in readings and determine if mastitis infection is present and, if so, in which quarter or quarters of the udder.

It is preferred that the circuitry include an indicator, see box 41, Figs. 4 and 5, to show when the battery becomes low and should be replaced. For this purpose, resistors R21 and R22 form a voltage divider between the five volt supply from power supply 38 and the minus four volt output of IC9, this being substantially across the full nine volts of the battery. Resistors R23 and R24 form a voltage divider for the five volt regulated output from IC6. The divided voltage between resistors R21 and R22 is supplied to one input terminal of a differential operational amplifier IC12 similar to IC2, while the divided voltage from between resistors R23 and R24 is supplied to the other input terminal of ICl 2.

As the battery discharges, the voltage across resistors R21 and R22 will decrease, while the regulated five volt supply wiE remain substantially constant. By adjusting the resistance values of the two dividers, the voltages on the two inputs to IC12 can be adjusted so that, as the battery discharges to a certain value, the difference in voltage on the two inputs to IC12 will have changed sufficiently to cause an output signal from IC12. Resistor R25 is a feedback resistor. The output of IC12 is connected to one input of exclusive "or" gates

IC13, IC14, and IC15, all of which may be included on a single chip, sueh as a CD4030 made by RCA. The other input terminal of "or" gates IC13, IC14 and IC15 are connected to an oscillator output of display driver IC5. As long as the output of IC12 is low, Le. zero volts, the output of the "or" gates IC13, IC14, and IC15 are in phase with the oscillator and no display is caused. When the battery becomes low, IC12 produces a high, Le. plus five volt, output causing the output of each of IC13, IC14 and IC15 to be out of phase with the oscillator. This out-of-phase input to the display ICll causes three decimal points to be displayed in the three righthand positions of the display on readout screen 25. These three decimal points provide a visual indication of a low battery.

OMPI It should be realized that some of the integrated circuits indicated, such as the differential operational amplifiers, the inverters, and the exclusive "or" gates, while being independent devices, may be included on a single chip. For example, the exclusive "or" gates IC13, IC14, and IC15 are all supplied on a single chip as identified, which includes an additional "or" gate not used. The operational amplifiers are also supplied on a single chip as identified, as are the inverters.

While, as indicated above, there are normally relatively small differences between conductivity values of milk from the four different quarter of a cow and from cow to cow of the same herd type, there are substantial differences in the normal conductivity values of milk from different herd types and in the conductivity value that is generally considered to be the threshold value indicative of the presence of mastitis. For example, a conductivity reading of 6118 u seimens is generally considered the threshold value to indicate the presence of mastitis in Jersey cows, while a value of 7157 u seimens is considered the threshold value for Holsteins.

As explained above, it is preferred that the instrument be calibrated so that a "5" indicates the threshold conductivity value and, thus, so that a "5" or above indicates an infected cow. It is undesirable to have to recalibrate the electronics each time the device is used with a different herd, or even to have to provide different instruments having different electronics calibrated to a particular type of cow.

It has been found that a change in calibration can most easily be made by changing the conductivity celL For a conductivity cell of the type shown, the reading varies depending upon the length of the cell (distance between the electrodes) and the cross-sectional area of the celL With a constant cross-sectional area, varying the length of the cell will give different readings with the same reference bridge. The length required is given by the following formula: _h _ CAR

10⁶

where L = length, C = conductivity, A = cross-sectional area, and R = resistance.

OMPI The resistance is the effective measured resistance of the conductivity cell necessary to give a reading of "5" on the display. This value will vary and is dependent upon the resistance of the reference resistor 31 and may vary with other specific circuit values. In the circuitry shown, with the reference resistor having a resistance of about 10k, it has been found that a conductivity cell resistance of about 11,787 ohms is needed to give a reading of "5". Thus, the length of the conductivity cell can be determined for any particular threshold value of conductance. Using a tube size of .125" inside diameter and the threshold value of 7157 u seimens for Holstein cows, the length of the conductivity cell must be 6.67 cm for the threshold value to produce a reading of "5". W^τith the same electronics and the same size tubing, the cell must be 5.7 cm long to give a reading of "5" for the threshold conductivity value of 6118 u seimen for Jersey cows. Figs. 6, 7, and 8 show an embodiment of the invention in which the conductivity cell is mounted so that it can be easily replaced with cells calibrated for different herd types.

In this embodiment, a removable frame 50 is received within recess 51 of a casing 52 that is similar to casing 10 of Figs. 1-3. A resiliant conical seal member 53 is positioned about a nipple-type connection fitting 54, one end of which is received by passageway 55 in the bottom of a milk reservoir 56 that is similar to reservoir 12b of Figs. 1-3. Conical seal member 53 is received by a similarly shaped receiving opening 57, so that a seal is formed and all milk from reservoir 56 is directed into nipple 54. Attached to the other end of nipple 54 where it passes through frame 50 is one end of a length 58 of flexible tubing, which leads to the conductivity cell and also serves as an air entrapment device. Its other end is attached to an end of a relatively short length 59 of stainless steel tubing which serves as one electrode of an electrical conductivity measurement cell identified generally as 60. Such cell is completed by connection of another length 61 of flexible tubing to an end of a second, relatively short length 62 of stainless steel tubing which serves as the second electrode of the conductivity measurement cell 60. The other end of stainless steel tubing 62 is connected to another length 63 of flexible tubing, whose other end is attached to discharge passage 64 which is preferably molded integrally with frame 50 and has an open end 65 communicating with the atmosphere through the bottom of frame 50.

Stainless steel tubing sections 59 and 62 are encased in frame 50 by means of insert piece 50a, which is glued into place on frame 50. A copper plate 66 is soldered to tubing 59 and extends about screw hole 67, so that a screw 68 passing through such hole will make electrical contact with plate 66 and, in turn, with tube section 59. A similar copper plate 69 is soldered to tubing section 62 and extends about screw hole 70 to make electrical contact with a screw 71 passing therethrough. Frame 50, with conductivity cell 60 secured therein, is inserted into casing 52 by inserting nipple 54 and seal 53 into receiving holes 55 and 57, respectively, and placing the frame against casing 52 in recess 51. Screws 68 and 71 are inserted through holes 67 and 70, respectively, and into receiving holes 74 and 75 in casing 52. Binding posts are provided within holes 74 and 75 in the casing, so that screws 68 and 71 serve to electrically connect the respective electrodes of the conductivity cell to the circuitry housed in casing 52. The circuitry is the same as that already described. Rubber stoppers 76 and 77 fit into holes 67 and 70 to seal them against build-up of dirt or other debris. It should also be noted that in the embodiment of Figs. 6-8, the battery (not shown) has been moved from its position as shown in Figs. 1-3 to a position inside casing 52. This provides room for insertion of frame 50 with its conductivity cell 60, and protects the battery from milk which may be spilled on the unit.

While a particularly effective hand-held device may be provided according to the invention, the invention may also be used in conjunction with various types of milk analyzing equipment or may be used in conjunction with milking machines to provide in line conductivity measurements of milk.

In milk analyzing equipment, samples of milk are generally drawn into such equipment, which then performs a series of tests on each sample. The flow-through conductivity cell of the invention may easily be placed in a milk sample line so that milk being drawn into the analyzing equipment or passing through the equipment at some point passes through such conductivity cell. The cell for such equipment is constructed similarly as described above, but, depending upon its location and the operation of the equipment, may be straight rather than looped and, if forced flow is provided for the sample, as is usually the case, may be horizontal in position rather than inclined. Thus,

OMPI as shown in Fig. 9, a non-conductive sample line 80 is provided with a flow- through conductivity cell made up of a short length of stainless steel tubing 81, a section of non-conductive line 82, and a second short length of stainless tubing 83. The electrodes of the cell, Le. stainless steel sections 81 and 82, are connected in the circuitry shown in Fig. 8, which is the same as that described and shown for Figs. 4 and 5 where indicated by the same block labels and numbers. In this embodiment of the invention, the same type of display is not needed and, generally, since sequential samples from the four quarters of the udder are not supplied, four sequential readings are not displayed simultaneously. Here, the digital output of the A/D converter 34 is connected to a digital computer, which could be a central data processing computer for the entire laboratory where the tests are made and evaluated or a microprocessing unit in the equipment itself which evaluates the signaL Further, in many cases, a meter output is desired, so the analog signal from the demodulator and amplifier 33 is also connected to an appropriate panel meter 84. Rather than an analog meter, a digital meter could be provided at the output of the A/D converter.

To provide in-line conductivity measurements during milking, a conductivity cell is provided in the milk line, preferably as close to the milking claw as possible and prior to the milk entering the main milk line. In this way, milk from a single cow is measured, rather than milk mixed from several cows. The conductivity cell is constructed in similar fashion to those described above, with an electrically conductive section at either end of an electrically non-conductive section. Since the conductivity cell must be completely full of milk to give an accurate reading of conductivity and since milking lines generally are designed so that they are not full, it is generally necessary to provide a bypass line of smaller diameter than the normal milking line and to provide a means for maintaining this line full of milk. Such means may merely be the difference in relative size of the two lines and the placement of the two lines so that there is always enough milk to fill the conductivity cell on a continuous flow basis, or a reservoir to ensure that there is enough milk to fill the line, or a valve or other flow restricting means in the conductivity cell line to restrict flow through the cell thus filling it up, or valve means to periodically block the cell line and cause it to

OMP fill with a sample to release such sample after measurement, and to block the line to again fill it.

As shown in Fig. 10, a reservoir 90 is provided in a milk line 91 so that milk will first fill the reservoir before continuing in the milk line. The milk in the reservoir feeds into a smaller non-conductive tube 92, wherein the conductivity cell is provided by stainless steel tube sections 93 and 94 separated by nonconductive tube 95. The milk is returned to the milk line by nonconductive tube 96.

The conductivity cell may be connected to electrical circuitry similar to that described above, and shown by block diagram in Fig. 9, wherein the blocks are as shown in and as described for Figs. 4 and 5. The output may be displayed on a digital meter or panel meter as previously described, or some other indicator, such as an LCD bar graph indicator, may be used. With a bar graph indicator, the analog output of the demodulator and amplifier 33 is fed to display driver 97, such as an LM 3914 made by National Semiconductor, which is connected to and drives a bar graph display 98, such as an MV57164 made by General Instrument.

While it is preferred to measure each quarter separately, so that readings for each quarter may be compared, most milking machines combine the milk from the four quarters at the claw so do not provide the opportunity for separate measurements. Some milking machines, however,- do provide separation of milk from the four quarters and, for these, separate readings can be obtained. In such instances, a conductivity cell as described above is placed in each of the four lines, and four sets of identical-electrical circuits as shown in Fig. 9, are provided to give four separate, continuous, conductivity readings. Alternately, the four cells could be multiplexed and processed sequentially and displayed as described for the hand-held version of the machine.

The electrodes for the conductivity cells have been described as stainless steel, but various other conductive materials may be used. However, stainless steel is preferred, since it is approved for use in dairy equipment and does not affect the milk.

Further, although the conductivity cells have been described and shown as short lengths of conductive tubing, with a length of non-conductive tubing therebetween, various other arrangements could be used, such as a length of

^ non-conductive tubing having longitudinally spaced-apart probes passing therethrough.

Whereas this invention is here illustrated and described with specific reference to embodiments thereof presently contemplated as the best mode of carrying out such invention in actual practice, it is to be understood that various changes may be made in adapting the invention to other embodiments without departing from the broader inventive concepts disclosed herein and comprehended by the claims that follow. Industrial Applicability As indicated above, the invention may be manufactured and used as a hand-held testing instrument for everyday use by a dairy farmer in testing his cows for the presence of mastitis; may be manufactured and used as a part of or as an add-on unit for milking machines for everyday use by a dairy farmer in testing his cows for the presence of mastitis; or may be manufactaured and used as a part of milk-analyzing equipment to test for the presence of mastitis at the same time that other tests are being made on the milk.

Claims

1. An electrical conductivity testing device for detecting mastitis in dairy cows, comprising means for receiving successive samples of milk to be tested; an electrical conductivity cell having a milk flow-through testing passage, one end of which passage is connected in fluid flow communication with the receiving means, so that milk will flow from said receiving means into and through said passage of the conductivity cell; means associated with said passage to insure that it is completely full of milk for electrical conductivity testing purposes; milk discharge means connected in fluid-flow communication with the other end of the conductivity cell to allow the sample to flow from the conductivity cell; and electrical means electrically connected to the conductivity cell for generating an electrical signal representative of the conductivity of the milk in the cell at any given time.

2. An electrical conductivity testing device in accordance with Claim 1, wherein the electrical conductivity cell has a pair of electrodes spaced apart in the milk flow-through testing passage longitudinally thereof, at least the portion of said passage between the electrodes being electrically non¬ conductive.

3. An electrical conductivity testing device in accordance with Claim 2, wherein the conductivity cell comprises two lengths of conductive tubing separated by a length of non-conductive tubing, and wherein the two lengths of conductive tubing are electrically connected to serve as the respective electrodes of the cell.

4. An electrical conductivity testing device in accordance with Claim 1, wherein the conductivity cell is removable and may be replaced by a conductivity cell of differing dimensions so as to adjust the device for use with different herd types.

5. An electrical conductivity testing device in accordance with Claim 4, wherein the conductivity cell is mounted on a frame and the frame is removable with respect to the device, so that the conductivity cell is replaced by replacing a frame having one conductivity cell mounted thereon with another frame having a different conductivity cell mounted thereon.

6. An electrical conductivity testing device in accordance with Claim 1, wherein the milk flow-through testing passage is configured in a loop with inlet and outlet located above the remaining portions of the passage so that milk to be tested enters the testing passage and remains there until forced out by an additional sample entering the passage.

7. An electrical conductivity testing device in accordance with Claim 1, wherein the comparing portion of the electrical means comprises a bridge amplifier circuit for sensing electrical impedance deviations of test samples in the conductivity cell from a reference impedance; and means for applying an alternating current reference voltage to said bridge amplifier circuit for impedance comparison purposes, whereby resultant electrical signals are produced by said bridge amplifier circuit indicative of the comparison values.

8. An electrical conductivity testing device in accordance with Claim

7, wherein the bridge amplifier circuitry comprises the conductivity cell; a reference resistor, both the conductivity cell and reference resistor being connected to the alternating current reference voltage in electrical parallel; a differential operational amplifier, one input of which is electrically connected to the conductivity cell and the other input of which is electrically connected to the reference resistor; a feedback resistor electrically connected between the output of the differential operational amplifier and the input connected to the conductivity cell; and a bias resistor electrically connected between a reference voltage and the input of the differential operational amplifier connected to the reference resistor.

9. An electrical conductivity testing device in accordance with Claim

8, wherein the feedback resistor and bias resistor both have substantially the same value of resistance.

10. An electrical conductivity testing device in accordance with Claim 7, wherein the electrical means includes means for demodulating and amplifying the resultant electrical signals, an analog to digital converter to which said electrical signals are applied, and a display driver for receiving the output from said converter and providing the comparison values to be displayed on the readout screen.

11. An electrical conductivity testing device for detecting mastitis in dairy cows, comprising an electrical conductivity testing cell; means for sequentially introducing into said cell and for sequentially discharging from said cell, a series of samples of milk taken from the four quarters, respectively, of the udder of a dairy cow; a readout screen providing for the display of four digits; electrical means for comparing a value obtained by said conductivity cell from a test sample of milk taken from one of the four quarters of the udder of a dairy cow, with a reference value and for energizing the display on the readout screen of a digit representative of the resulting comparison value; and switch means for setting said electrical means into respective conditions for energizing the display on the readout screen of digits representative of comparison values obtained for respective test samples from the other three quarters of the udder of said dairy cow, while retaining the digit displays already energized.

12. An electrical conductivity testing device in accordance with Claim

11, wherein the comparing portion of the electrical means comprises a bridge amplifier circuit for sensing electrical impedance deviations of test samples in the conductivity cell from a reference impedance; and means for applying an alternating current reference voltage to said bridge amplifier circuit for impedance comparison purposes, whereby resultant electrical signals are produced by said bridge amplifier circuit indicative of the comparison values.

13. An electrical conductivity testing device in accordance with Claim

12, wherein the bridge amplifier circuitry comprises the conductivity cell; a reference resistor, both the conductivity cell and reference resistor being connected to the alternating current reference voltage in electrical parallel; a differential operational amplifier, one input of which is electrically connected to the conductivity cell and the other input of which is electrically connected to the reference resistor; a feedback resistor electrically connected between the output of the differential operational amplifier and the input connected to the conductivity cell; and a bias resistor electrically connected between a reference voltage and the input of the differential operational amplifier connected to the reference resistor.

14. An electrical conductivity testing device in accordance with Claim 12, wherein the electrical means includes means for demodulating and amplifying the resultant electrical signals, an analog to digital converter to which said electrical signals are applied, and a display driver for receiving the output from said converter and providing the comparison values to be displayed on the readout screen.

15. An electrical conductivity testing device in accordance with Claim 14, wherein the electrical means also includes switches whose outputs are applied to the display driver for preventing more than one of the four digits to be energized by the converter at a time and for latching previously energized digits in their energized state.

16. An electrical conductivity testing device in accordance with Claim 11, wherein the electrical conductivity testing cell and the electrical means are compactly housed in a casing adapted to be hand held and having a window aperture which frames the readout screen.

17. An electrical conductivity testing device in accordance with Claim

11, wherein the reference value is chosen and the circuitry is constituted such that any digit obtained on the display that is above a preset minimum indicates the presence of mastitis infection in the corresponding quarter.

18. An electrical conductivity testing device in accordance with Claim 11, wherein the reference value is chosen and the circuitry is constituted such that any digit obtained on the display that is three or more counts above any other digit indicates the presence of mastitis infection in the corresponding quarter.

19. An electrical conductivity testing device in accordance with Claim 11, wherein the conductivity cell comprises two lengths of conductive tubing separated by a length of nonconductive tubing, and wherein the two lengths of conductive tubing are electrically connected to serve as the respective electrodes of the celL

20. An electrical conductivity testing device in accordance with Claim 19, wherein the conductivity cell is positioned in a housing having a top formed as an open funnel for receiving a sample of milk to be tested; and wherein an electrically nonconductive tube leads from the funnel to the conductivity cell, so that the sample of milk will flow from the funnel through the conductivity celL 21. An electrical conductivity testing device in accordance with Claim

20, wherein the nonconductive tube and the entrance thereinto from the funnel are such that, when a sample of milk is introduced into the funnel following discharge from the funnel of a preceding sample, a bubble is formed in such tubing and moves in advance of the later sample to flush any remnants of the preceding sample from the conductivity celL

22. An electrical conductivity testing device in accordance with Claim

21, wherein the milk flow-through testing passage is configured in a loop with inlet and outlet located above the remaining portions of the passage so that milk to be tested enters the testing passage and remains there until forced out by an additional sample entering the passage.

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23. An electrical conductivity testing device in accordance with Claim 11, wherein the conductivity cell is removable and may be replaced by a conductivity cell of differing dimensions so as to adjust the device for use with different herd types.

24. An electrical conductivity testing device in accordance with Claim

23, wherein the conductivity cell is mounted on a frame and the frame is removable with respect to the device, so that the conductivity cell is replaced by replacing a frame having one conductivity cell mounted thereon with another frame having a different conductivity cell mounted thereon.

25. An electrical conductivity testing device in accordance with Claim

11, wherein the readout screen is arranged to display the four digits side-by- side.