GB2080540A - Electrical apparatus for weighing animals - Google Patents

Abstract

Weighing apparatus has a load cell 10 connected to an amplifier 12, filter circuit 14 and analogue/digital converter 16, of which the output drives a digital weight indicator 18. The response characteristics of the apparatus can be controlled during the course of weighing to alter the sensitivity to sudden weight changes and provide in sequence relatively light and relatively heavy damping, thereby to give a short settling time followed by a steady readout even with erratic movement of the animal. This may be achieved by switching selectively to alter the time constant of the filter circuit 14, or, in a microprocessor based embodiment, a switching arrangement may be arranged to alter the manner of processing the signal by the microprocessor. <IMAGE>

Description

SPECIFICATION Apparatus for weighing animals This invention relates to apparatus for weighing live animals, especially farm animals for example such as pigs or sheep, the apparatus being of the kind wherein a load supporting structure for receiving and supporting the animal to be weighed is operatively associated with transducer means arranged to provide an electrical signal representative of the magnitude of the applied load, this signal then being processed in a signal processing section of the apparatus to provide an output which is applied to drive weight indicator read-out or display means.

In practice, the load supporting structure commonly comprises a platform which may be arranged for the animal to walk onto or it may comprise a cage, often termed a "crush", having an openable door for entry of the animal.

With such apparatus, however, a problem arises because the animal generally has some freedom to move to some extent on the load supporting structure and the resulting highly unpredictable movements of the animal which normally occur produce unpredictable erratic transient or oscillating variations in the output signal which, in the absence of some remedial measures, would give a very unsteady read-out and make it difficult to determine the proper weight. To meet this difficulty it has therefore been customary either to incorporate means for reducing the sensitivity of the apparatus, and thereby producing a heavy damping effect and sluggish movement to neutralise the erratic variations, or to arrange for the instantaneous weight readings to be sampled and averaged over a period of several seconds.Both these methods, however, have the disadvantage that the settling time, i.e. the time needed to take a reading, is unduly prolonged and is generally considerably longer than is desirable for high efficiency, comparing very unfavourably with minimum weighing times generally experienced with conventional weighing machines used for weighing static loads.

It is accordingly an object of the present invention to provide apparatus of the kind referred to for weighing animals in which the above-mentioned disadvantages can be reduced in a convenient and effective manner, giving a relatively short settling time with a steady read-out.

A feature of the invention is that the signal processing section of the apparatus is provided with controllable means for altering during the course of a weighing operation the response characteristics thereof in respect of erratic transient or oscillating variations in the signal thereby to alterthe sensitivity of the apparatus to sudden changes in weight and to select in sequence alternative modes of operation giving relatively light damping characteristics and relatively heavy damping characteristics respectively.

The apparatus may be designed su that the alteration in response characteristics is carried out by a switching operation which may be either under manual control or, by providing a suitable sensor possibly in association with time delay means, under automatic control responsive to completion of preliminary preparatory operations for weighing the animal.

Preferably the signal processing section includes an analogue to digital converter and applies a digital drive output to the weight indicator read-out or display means.

In some embodiments the alteration in response characteristics is conveniently achieved by arranging for operation of a switch device to alter the time constant of a CR combination in a filter circuit of the signal processing section, as by switching of different capacitors in the filter circuit for example.

However, any switching operation should be such that it does not itself cause any significant additional disturbance which would hinder obtaining a short settling time, and in one preferred arrangement a filter circuit is provided that includes a unity gain operational amplifier and a time constant control capacitor arranged to be switched alternately to input and output terminals of the amplifier which are at substantially the same potential under working conditions.

In other embodiments the signal processing section may incorporate, in addition to an analogue to digital converter, a microprocessor which is arranged and programmed to compute the weight value to be displayed based on an average of a predetermined number of sample weight data values which are taken by the analogue to digital converter, and the alteration in response characteristics in accordance with the invention is conveniently achieved by arranging for operation of a switch device to alter the mode of operation of the microprocessor and modify the manner of computation so as to change the effect of sudden changes in weight data values, as for example by altering the number of sample values averaged for each computation and/or by altering an operational routine of the microprocessor for selective processing the weight data values according to their extent of sequential variation.

By way of example, embodiments of the invention will be more particularly described, with reference to the accompanying drawings, in connection with a digital read-out electronic weighing machine for farm animals that represents a type of weighing apparatus for which the invention is especially suited.

In the drawings: Figure 1 is a simplified diagram showing the general schematic layout of the electronic system of the machine according to a first embodiment; Figure 2 is a diagram showing circuit details of a filter component of the system of Figure 1; and Figure 3 is a diagram showing the general schematic layout of the electronic system of the machine according to a second embodiment.

The complete weighing machine of both embodiments will include a movable platform or cage forming the load supporting structure (not shown) for receiving and supporting the animal concerned, a pig for example, this platform or case being operatively connected either directly or by way of a lever mechanism to a transducer, such as a strain gauge type load cell indicated at 10 and 10' in Figures 1 and 3, which provides an electrical analogue signal representative of the weight of the animal.

This signal is then processed in a signal processing section which, in the embodiment of Figures 1 and 2, comprises a first stage signal amplifier 12, a following stage low pass active filter 14 and an anlogue-to-digital converter 16, the output of the latter than being applied to drive a digital weight indicating display unit 18.

As shown in Figure 2, in the filter 14the input analogue signal is fed through a resistor R1 to a capacitor Cy and the non-inverting input of a unity gain operational amplifier Al, and a further capacitor Cx is provided which is connected selectively through switch S1 either to the output of amplifier Al ortho the non-inverting input of the latter in parallel with Cy.

When operating with Cx in parallel with Cythe time constant of the filter is thereby increased so that the sensitivity to erratic transient or oscillating variations in the signal is reduced and relatively heavy damping characteristics are obtained, but when Cx is connected to the output of Al the time constant is less and there is only a relatively light damping effect. It should be noted that with this arrangement, when switching from the light damping mode of operation to the heavy damping mode of operation, the voltage of the capacitor Cx, corresponding to the voltage of the output of amplifier Al, is very close to the voltage at the non-inverting input so that a substantially "stepless" transfer takes place in changing between the two filter time constants, thereby avoiding causing any significant additional disturbance to the circuit.

The switch S1 is conveniently operated by a relay 20 which can be of any suitable type although a solid state type relay using fet devices or integrated circuits will generally be most appropriate, and this relay 20 is in turn controlled by an external switch S2.

This external switch 22 may be either "normally closed" or "normally open" depending on the required manner of operation of the apparatus, and it may be designed either for manual operation, for example a push button, or for automatic operation.

In the latter case it will be incorporated in a sensor, such as a proximity limit switch, photo-electric device etc., which may be carried on or associated with the weighing platform or cage so as to respond to the presence of the animal andlor closure of the cage.

Several different ways of operation are possible, in each of which the time constant of the active filter 14 is changed in response to actuating the external switch S2 to operate the relay 20 and switch S1, whereby the apparatus operates in a lightly damped mode for a short period followed by a relatively heavily damped mode so as to give a rapid settling time followed by a steady read-out.

Thus, in a first arrangement, with a manually operated push button type external switch S2, the switching may be set so that the apparatus normally operates in its more heavily damped mode, but when the animal is on the load supporting structure ready for weighing the operator presses the push button for a short period, e.g. about one second, so as to change to the lightly damped mode and the push button is then released so that the heavily damped mode of operation is restored and the display or read-out steadies.

In a second arrangement, with a cage for containing the animal, the external switch S2 forms part of a sensor (not shown) arranged to detect closing of the cage door. When the cage door is open, the switching is set so that the apparatus operates in its heavily ~ damped mode but when the door is closed after the animal has entered the external switch is automatically actuated to cause the apparatus to change to its lightly damped mode of operation for a short period, sufficient to give a rapid settling time, before changing back to the more heavily damped mode to provide a steady read-out. In this case, a time delay device may be incorporated to actuate the switching to restore the more heavily damped mode.

In a third arrangement, with a "walk on" platform to receive the animal, the switching may be set so that the apparatus or machine normally operates in its lightly damped mode and the external switch S2 forms part of a sensor arranged to detect the presence of the animal on the platform. This sensor then responds, after a short time delay if required, to actuate the switch S2 and cause the relay 20 and switch S1 to operate to increase the filter circuit time constant and change the operation of the apparatus or machine to the more heavily damped mode, again to provide a steady read-out after a rapid settling time.

In modified arrangements, if desired, the switch S1 could alternatively be operated directly, such as buy a press button, instead of through a relay, as described.

In the second embodiment, illustrated in Figure 3, the electrical analogue signal from the load cell 10' is processed in a signal processing section comprising a signal amplifier 12' associated with an offset generator circuit 30 and a variable attenuator 32, a filter network 14', an analogue to digital converter 16' and a microprocessor 34 from which the output feeds a digital display driver unit 36 to drive a digital display 18'.

More particularly, the signal amplifier 12' is conveniently designed to operate in "single ended" mode ; to amplify the load cell signal by fifty times, and receives an offset voltage from the offset generator 30 to provide a suitable zero or base signal voltage level in the unloaded condition of the load cell 10' in accordance with a known technique. The signal from the amplifier 12' is attenuated by the variable attenuator 32 which is adjusted so as to set the overall gain or span, and it is then fed via the filter network 14' which has predetermined fixed characteristics to the analogue to digital converter 16' which functions in association with the microprocessor 34.

The analogue to digital converter 16' is preferably a dual slope integrating type such as the integrated circuit ICL7109 manufactured by Intersil Corporation of U.S.A.; and the microprocessor 34 used in conjunction therewith is conveniently, in this example, a single chip type PIC 1656 of General instrument Corporation, U.S.A. which incorporates internal RAM and ROM storage as well as input/output (I/O) ports and requires only an external crystal "clock" generator 38 to operate. Pulses derived from the same "clock" generator 38, suitably divided by a frequency divider 40 are also supplied to the analogue to digital converter 16' which is further linked through a strobe line to the microprocessor 34 so that the converter and microprocessor operate synchronously.In this arrangement the converter 16' is advantageously used in ratiometric mode, that is, the output represented by the digital count of clock pulses on the status line interconnection 45 with the microprocessor is in reality a measure of the ratio between the loadcell excitation voltage (Ve) and the load cell voltage output signal.

The microprocessor 34 is also connected through the preset option calibration links section 42, which enables connections in the equipment to be set up initially by the manufacturer to suit the intended particular animal weighing application and provide an appropriate weighing range for example, to a keyboard 48 for manual control of various certain functions such as selecting gross and nett weights (automatic taring facility), checking the zero setting during the course of weighing operations, etc. And, in particular, the keyboard 48 includes a push-button switch Sd which effectively control the response characteristics and degree of damping of the apparatus as hereinafter described.

Multiplexed coded digital weight data is output from the microprocessor to the display driver 36, e.g.

an "Intersil" ICM 7235, where it is "latched" and decoded to seven segment form for driving the digital display 18' which conveniently comprises a 4-digit vacuum fluorescent type.

The microprocessor 34 is arranged and programmed to compute the digital weight value to be displayed based on averaging a predetermined number of sample weight data values provided by a corresponding number of conversions carried out by the analogue to digital converter 16'. Thus, the individual values of this predetermined number of successive conversions will be stored and then divided by the number concerned to give the average, and this average can then be used directly or, preferably, it will be selectively further processed according to the operational routine determined by the programming of the microprocessor to take into account the extent of sequential variations or differences in arriving at the final computation whereby less weighting is given to those values for which the sequential variations or differences are unduly large, indicative of a sudden transient.

This averaging and selective processing in effect determines the response characteristics and degree of damping, and is controlled by operation of the press-button switch Sd. Thus, it may be arranged in this example so that normally the number of samples or conversions averaged and the selective processing carried out is such that the apparatus exhibits a relatively low sensitivity to sudden changes in weight, that is, it has relatively heavy damping characteristics, but when the switch Sd is actuated the number of samples or conversions averaged will be reduced and/orthe operational routine of the microprocessor 34 will be altered to reduce the effect or degree of the selective processing, that is, the manner of computation is temporarily modified, such that the apparatus then exhibits relatively light damping characteristics thereby enabling a relatively short settling time to be achieved.

The switch Sd is therefore functionally equivalent in overall effect to the switch S2 of the first embodiment, and again various different arrangements of the switch function are possible depending on the required manner of operation of the apparatus and whether, for example, control is to be solely manual or automatic.

Claims (11)

1. Apparatus for weighing live animals, especially farm animals for example such as pigs of sheep, comprising a load supporting structure arranged to receive and support the animal to be weighed, transducer means operatively associated with said load supporting structure so as to provide an electrical analogue signal representative of the magnitude of the applied load, and a signal processing section arranged to process said signal so as to provide an output that is applied to drive weight indicator read-out or display means, wherein said signal processing section has controllable means for altering during the course of carrying out a weighing operation the response characteristics in respect of erratic transient or oscillating variations in the signal thereby to alter the sensitivity of the apparatus to sudden changes in weight and to select in sequence alternative modes of operation giving relatively light damping characteristics and relatively heavy damping characteristics respectively.

2. Apparatus as claimed in claim 1 wherein said controllable means for altering the response characteristics includes a switch device which, in orderto provide successively the relatively light and relatively heavy damping modes of operation of the apparatus, is operable under manual control.

3. Apparatus as claimed in claim 1 wherein said controllable means for altering the response characteristics includes a switch device which, in order to provide successively the relatively light and relatively heavy damping modes of operation of the apparatus, is arranged to operate under automatic control of a sensor responsive to completion of preliminary preparatory operationsforweighing the animal.

4. Apparatus as claimed in claim 2 or 3 wherein the switch device is further controlled by time delay means.

5. Apparatus as claimed in any of claims 2 to 4 wherein the signal processing section includes an analogue to digital converter and applies a digital drive output to the weight indicator read-out or display means.

6. Apparatus as claimed in any of claims 2 to 5 wherein operation of the switch device is arranged to alter the time constant of a CR combination in a filter circuit, through which the analogue signal is passed, in the signal processing section in order to change the response characteristics.

7. Apparatus as claimed in claim 6 wherein the switch device operates to change the circuit connections of a time constant control capacitor in the filter circuit.

8. Apparatus as claimed in claim 7 wherein the switch device operates alternately to switch the time constant control capacitor to input and output terminals of an operational amplifier which are at substantially the same potential under working conditions.

9. Apparatus as claimed in claim 5 wherein the signal processing section further includes a microprocessor which is arranged and programmed to compute the weight value to be displayed based on an average of a predetermined number of sample weight data values which are taken by the analogue to digital converter, and in order to change the response characteristics operation of the switch device is arranged to alter the mode of operation of the microprocessor and modify the manner of computation so as to change the effect of sudden changes in weight data values.

10. Apparatus as claimed in claim 9 wherein operation of said switch device is arranged to cause a change in the predetermined number of sample weight data values averaged for each computation by the microprocessorand/orto cause a change in an operational routine of the microprocessor for selectively processing the sample weight data values according to their extent of sequential variation.

11. Apparatus for weighing live animals substantially as herein described and illustrated with referpence to Figures 1 and 2 or to Figure 3 of the accompanying drawings.