GB2102950A

GB2102950A - Sensor systems for particles

Info

Publication number: GB2102950A
Application number: GB08123610A
Authority: GB
Inventors: John Harbour
Original assignee: Probe Engineering Co Ltd
Current assignee: Probe Engineering Co Ltd
Priority date: 1981-08-01
Filing date: 1981-08-01
Publication date: 1983-02-09
Also published as: GB2102950B

Abstract

The grain loss in a combine harvester can be detected by impact sensors, but different types of grain give different amplitude responses. In order to set a sensor system to optimum performance, a sample of the grain to be harvested is sprayed over a sensor (1). The impacts generate pulses which are fed through a gain controlled amplifier (2) to threshold detectors (5, 6) set at different levels. These distinguish the impact levels and govern a gain control circuit (9, 10, 11, 12, 21) which adjusts the amplifier so that the sample signals average at the higher threshold. For the working mode, a second gain control circuit (15) takes over and reduces the amplifier's gain so that the two thresholds define the limits of a band in which useful signals are accepted, with the average impact determined by the sampling adjustable within that band. Indicators (13, 18, 20) are provided to show the state of the setting up procedure to the operator. <IMAGE>

Description

SPECIFICATION Improvements relating to sensor system for particles This invention relates to a sensor system for particles, and is particularly, although not exclusively, concerned with the sensing of grain in combine harvesters.

Typically grain sensors are provided to detect the grain, which does not pass in to the main grain duct of a combine harvester, to provide an indication of grain loss. The response of such sensors varies with grain size and in practice the sensitivity of the sensor has to be adjusted each time the combine is used. The adjustment normally takes the form of manually altering the gain control of the sensor amplifier, until the operator observes that the operating conditions of the sensor are acceptable. These conditions are normally selected on the basis of experiment and the operator's experience. The aim of this invention is to provide a sensor which is more readily set-up.

According to the present invention there is provided a sensor system for particles, such as for grain loss in combine harvesters, wherein a sensor output is applied to detecting means via a gain controlled amplifier providing sensitivity adjustment, comprising a pair of different level threshold detectors to which input signals from the amplifier are applied, and a gain control circuit governed by the detectors to reduce the gain when the preponderance of signals exceed the higher threshold and to increase the gain when the preponderance of signals is between the thresholds.

Preferably means are provided to inhibit the gain control circuit after a generally predetermined period has elapsed, a predetermined number of pulses have been received and/or when the gain has reached a steady state or is oscillating about a particular value, such that circuit holds the gain value existing when the circuit is inhibited.

A further gain control circuit may be provided for increasing or decreasing the gain of the amplifier by or to a predetermined fraction of the inhibit gain value. Conveniently the further gain control circuit operates generally when the first gain control circuit is inhibited.

The first gain control circuit may include a counter arranged to count up when an impact signal falls between the thresholds and down when an impact exceeds the thresholds or vice versa. In this case the output of the counter is the gain control signal, which may be converted to an analogue signal. The system may be arranged such that when it is initially activated the counter achieves that count, which represents a state of maximum sensitivity.

The inhibit means may be arranged to disable the counter a predetermined time after a first impact signal lying between the thresholds has been detected or after a predetermined number of such impacts.

The system may include a circuit for displaying the rate and/or quantity of grain loss and/or for providing a warning when the grain loss is excessive. The circuit may also indicate when the sensor is not adjusted.

From another aspect the invention may provide a sensor system for particles, such as for grain loss in a combine harvester, wherein a sensor output is applied to detecting means, the detecting means including means for determining the mean impact of a sample of particles striking the sensor and means for adjusting the detecting means to detect only impacts, which fall within a predetermined band width about the mean.

For the purposes of the specification, the term "mean" is not limited to its strict mathematical meaning but covers any broad indication of the statistical peak of the impacts of the sample of particles.

The band width may be centred on the mean or the mean may lie in any preselected position within the band width. In a preferred embodiment the mean lies adjacent the lower end of the band width.

From a further aspect the invention provides a sensor system for particles, such as for grain loss in a combine harvester, wherein the sensor output is applied to detecting means, the detecting means including control means for automatically adjusting the sensitivity of the of the system in response a sample of particles striking the sensor when the the system is in a "prime" mode and for maintaining the sensitivity or a predetermined proportion thereof when the system is in a "ready" or "run" mode.

Preferably the system automatically transfers from its "prime" mode to its "ready" mode when the sensitivity has been adjusted.

In any of the above cases it is preferred that the detecting means return to an insensitive state whenever the apparatus with which it is associated is switched off. In this arrangement a manual control is normally provided for putting the detecting means into a sensitive or "prime" mode.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a graph showing the response of a grain sensor; Figure 2 is a block diagram of an electrical circuit associated with a grain sensor; Figure 3 is a diagram for explaining the operation of Figure 2; and Figure 4 is a block circuit diagram of a display circuit.

Figure 1 shows the response of a sensor to the impact of grain in statistical terms. Some grains will impact lightly and produce a very small detected signal, others will strike the sensor hard and generate a very high detected signal, but the majority of grains will produce signals over a fairly narrow band between these extremes. However, this band will not be the same for every type of grain. For example rye generally produces low amplitude signals, while oats, barley and corn all produce progressively higher amplitude signals.

Thus, a sensor must be able to respond to the different levels of signal, preferably over the appropriate narrow band embracing the peak of the graph as shown in Figure 1.

Referring to Figure 2, a piezo-electric crystal 1 on the grain sensor feeds its signal to a band-pass amplifier 2 with gain control inputs. Its output is in turn passed through a detector 3, a differentiator circuit 4, which removes any steady signal such as that due to electrical noise, and thence to the inputs of two comparators 5 and 6.

These have threshold inputs 7 and 8, and the comparator 5 opens to a lower threshold than the comparator 6.

The output of the comparator 5 is to a differentiator 9 which has two outputs, one conveying a pulse representing the leading edge of the comparator 5 output to the set input of a flip-flop 10 and the other a pulse representing the trailing edge of that output, this going to a clock input of a counter 11 and to a trigger input of a monostable 12. The reset input of the flip-flop 10 is from the comparator 6, and its Q output is applied to an enable input of the monostable 12 and to an up-down input of the counter 11. The monostable 12 when triggered energises a green LED 13, and its output is also applied to a delay circuit 14 and thence to the reset input of a flipflop 15.

A further flip-flop 16 has a power-on signal to its set input and a signal from a button 1 7 to its reset input, this also being applied to the counter 11 and to the set input of flip-flop 1 5. The Q output of the flip-flop 16 also goes to this set input, to a red LED 18 and presets the counter.

The Q output of flip-flop 1 5 goes to a gate 1 9 and to an enable clock input of the counter 11, and the gate 19 governs an orange LED 20. The four most significant bits (MSB) outputs of the counter are applied to a digital-analogue (DA) circuit 21, whose output is a gain control for the amplifier 2.

The counter is inhibited from "counting round" from a maximum or minimum count by the loop 22.

When power is first applied, flip-flop 1 6 energises the red LED 18, which indicates the "reset" state. The continuous current drawn by this light is used to signal to the cab unit that the sensor is in this state and not adjusted to deal with grain. The green and orange LEDs 13 and 20 are not energised at this time.

To adjust the sensor, the operator presses the button 1 7 which resets flip-flop 1 6 and thus extinguishes the red LED 18, sets the flip-flop 1 5 and thereby energises the orange LED 20 and enables the clock counter, and presets the counter to its maximum count. The sensor is now in the "prime" state ready to be set up and at maximum sensitivity.

Grains of the'type to be combined are then scattered on the sensor from the correct height, and since it is at maximum sensitivity they will readily be detected, causing both comparators 5 and 6 to exceed their threshold. Opening of the high threshold comparator 6, necessarily occurring after that of the low threshold comparator 5 as indicated by Figure 3, resets flipflop 10 and thereby causes the counter 11 to count down, slowly reducing the gain of the amplifier 2 via the D-A circuit 21. As this gain falls, the threshold of comparator 6 will no longer be exceeded and only comparator 5 will operate, setting the flip-flop 10 and causing the counter to count up again, slowly increasing the gain. A balance is soon reached, at which the counter counts up and down on an average equally.In other words, about half the grain impacts exceed the threshold of comparator 6 and the other half are below it.

When the detected signals are between thresholds, the flip-flop 10 is set and so the monostable 12 is enabled and triggered by trailing edge signals, each for a brief fixed period, say 5 mS. This causes the green LED 13 to flash with each impact registered by comparator 5 only. Eventually the flip-flop 1 5 is reset via the delay 14, extinguishing the orange LED 20, and the circuit moves automatically into the "ready" state by disabling the counter to "freeze" the gain signal on D-A circuit 21 and simultaneously reducing the gain of the amplifier 2 to a predetermined fraction of the gain signal determined by the counter 11. This reduction in gain occurs because the resetting of flip-flop 15 results in a "low" signal on the gain control input 22 of the amplifier 2.

It will be appreciated thar an alteration in the gain of the amplifier 2 is equivalent to an alteration in the thresholds of comparators 5 and 6. Thus the predetermined reduction in gain has the effect of raising the threshold of comparator 5 to just below the balance threshold which the comparator 6 achieved in the "prime" mode.

Similarly the threshold at comparator 6 is raised so that the monostable 1 2 will only be triggered by impacts having a momentum around the "average" determined during the "prime" mode.

Obviously the width of the band determined by the comparators 5 and 6 and its relationship to the "average" can be adjusted to suit particular machines, working conditions, etc.

The brief current pulses from the monostables are detected by the cab unit and averaged to provide a loss signal. Meanwhile the operator setting up the sensor can observe the green light and know that the gain setting is nearly complete.

Figure 4 shows a circuit for displaying the impacts registered by the sensor as falling within the band determined by comparators 5 and 6. The circuit includes a comparator 23, which has its inputs 24 connected across a resistor 25 disposed in the power supply to the circuit of Figure 2. The output of comparator 23 is fed via a low pass filter 26 to an operational amplifier 27, the output of which is displayed on a voltmeter 29. The output of amplifier 27 is also fed to one input of a comparator 30, the other input of which receives a square wave signal from a free running oscillator (not shown). If the output of amplifier 27 exceeds the lower level of the square wave the comparator 30 will switch and causes an indicator light 31 to flash. If the output exceeds both levels of the square wave the light will burn continuously.

Normally the current drawn by the circuit of Figure 2 is very low. However if the "reset" or "prime" lights are on or if the monostable is triggered, a much larger current flows. This current flow is detected by the comparator 23, smoothed by filter 26 and displayed on the meter 29. During normal operation the voltage displayed represents the monostable pulses and hence is an indication of grain loss; if the grain loss becomes excessive light 31 will flash, if the loss becomes very large or if the circuit is in its "prime" or "reset" mode the light will burn continuously to warn the operator that the sensor has not been adjusted.

Frequently the combine will have a number of sensors. With this arrangement a single push button could be used to prime all of the sensors and their modes can be displayed individually by a single set of lights or even a single light. Similarly the gain loss can be displayed for each sensor or summed to provide a single indication. The push button could be placed in a protected slot to allow it to be pressed only by the ignition key, to ensure that sensors are not adjusted while the engine is running.

Claims (filed on 29.7.82) 1. A sensor system for particles, such as for grain loss in combine harvesters, wherein a sensor provides impact signals of various amplitudes, the system comprising means operative during a sampling period for determining from said signals an average impact level from a sample of particle impacts, and detecting means adjustable to indicate signals in a predetermined band width about said average.

2. A sensor system as claimed in claim 1, wherein the adjustment of the detecting means is governed by the determining means.

3. A sensor system as claimed in claim 1 or 2, wherein the detecting means includes an amplifier and the determining means includes a threshold detector which receives the amplifier and detected impact signals, there being means for altering the threshold in response to the impact signals to a value at which the average impact signals, after amplification, correspond to that threshold.

4. A sensor system as claimed in claim 3, wherein the amplifier has gain control and there is a gain control circuit responsive to the threshold detector during the sampling period to adjust the gain and thus, in effect, the threshold.

5. A sensor system as claimed in claim 4, wherein a second threshold detector, with a lower threshold than the first, also receives the amplified and detected impact signals, and is arranged to enable the gain control circuit when this lower threshold is exceeded.

6. A sensor system as claimed in claim 5, wherein the gain control circuit includes a counter arranged to count in one direction when an impact signal falls between the thresholds and in the opposite direction when an impact signal exceeds the higher threshold.

7. A sensor system as claimed in claim 6, wherein a digital-analogue converter transforms the output of the counter into an analogue gain control signal for said amplifier.

8. A sensor system as claimed in claim 6 or 7, wherein the counter is arranged to achieve a state giving maximum sensitivity to said amplifier when initially activated.

9. A sensor system as claimed in any one of claims 3 to 8, wherein means are provided for effectively reducing at the end of the sampling period the threshold at which the first threshold detector responds.

10. A sensor system as claimed in claim 9, wherein the reducing means comprises a further gain control circuit to which the amplifier responds.

11. A sensor system as claimed in claim 9 or 10, as appendant to claim 4, wherein the first gain control circuit is rendered inoperative after the sampling period.

1 2. A sensor system as claimed in any preceding claim, wherein means are provided for terminating the sampling period and for triggering the adjustment of the detecting means.

13. A sensor system as claimed in claim 12, wherein the terminating means is a timing circuit set in operation by the sampling.

14. A sensor system as claimed in claim 13, as appendant to claim 5, wherein the timing circuit is set in operation in response to the lower threshold being exceeded.

1 5. A sensor system as claimed in claims 5 and 9 and any other preceding claim, wherein after the sampling period the threshold detectors serve to define said predetermined band width, there being indicator means responsive to impact signals between thresholds.

1 6. A sensor system as claimed in claim 15, wherein the indicator means includes a first indicator for showing the integrated impact level and a second indicator for showing when the higher threshold is exceeded.

1 7. A sensor system substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. receives a square wave signal from a free running oscillator (not shown). If the output of amplifier 27 exceeds the lower level of the square wave the comparator 30 will switch and causes an indicator light 31 to flash. If the output exceeds both levels of the square wave the light will burn continuously. Normally the current drawn by the circuit of Figure 2 is very low. However if the "reset" or "prime" lights are on or if the monostable is triggered, a much larger current flows. This current flow is detected by the comparator 23, smoothed by filter 26 and displayed on the meter 29. During normal operation the voltage displayed represents the monostable pulses and hence is an indication of grain loss; if the grain loss becomes excessive light 31 will flash, if the loss becomes very large or if the circuit is in its "prime" or "reset" mode the light will burn continuously to warn the operator that the sensor has not been adjusted. Frequently the combine will have a number of sensors. With this arrangement a single push button could be used to prime all of the sensors and their modes can be displayed individually by a single set of lights or even a single light. Similarly the gain loss can be displayed for each sensor or summed to provide a single indication. The push button could be placed in a protected slot to allow it to be pressed only by the ignition key, to ensure that sensors are not adjusted while the engine is running. Claims (filed on 29.7.82)

1. A sensor system for particles, such as for grain loss in combine harvesters, wherein a sensor provides impact signals of various amplitudes, the system comprising means operative during a sampling period for determining from said signals an average impact level from a sample of particle impacts, and detecting means adjustable to indicate signals in a predetermined band width about said average.