GB2092778A

GB2092778A - Ventilation Controllers

Info

Publication number: GB2092778A
Application number: GB8136047A
Authority: GB
Original assignee: VENTEC AGRICULTURAL Ltd; Pickering Electronics Ltd
Current assignee: VENTEC AGRICULTURAL Ltd; Pickering Electronics Ltd
Priority date: 1980-11-29
Filing date: 1981-11-30
Publication date: 1982-08-18
Also published as: GB2092778B

Abstract

An electronic control apparatus Fig 1 is arranged to cause a ventilator to open or close dependent upon the deviation of the sensed temperature from a pre-selected required value, set at 17. In response to a sensor 10 detecting a temperature deviation greater than a particular amount, the motor of the ventilator is energised in the appropriate sense for a limited period. This period is either manually pre-set at 19 or determined by the apparatus dependent upon the magnitude of the deviation from the required value (Figure 3). If the sensed temperature is greater than the required value by a greater amount, then a circulation boost fan is energised, whereas if it is smaller than the required value by a greater amount, then a heater is energised. Once energisation of the ventilator motor has occurred further energisation thereof is inhibited for a fixed period, selected at 20, to give time for equilibrium to be established. The application to livestock roaring pens is contemplated. <IMAGE>

Description

SPECIFICATION Ventilation Controllers This invention relates to electronic control apparatus for an electrically-actuated ventilator, as well as a complete ventilation system including an electrically-actuated ventilator together with an electronic controller therefor.

It is desirable in many environments to attempt to maintain some atmospheric parameter substantially constant within a given area, notwithstanding variations in that parameter externally of that area or sources of variation within that area. Often, it is advantageous to have the parameter maintained substantially constant by automatic means, so as both to increase responsiveness to changes internally and externally of the area and to reduce the manpower required as well as the likelihood of errors occurring with a manual system.

One particular field where it is important to maintain the environmental parameter of temperature substantially constant and yet it is also important that costs are kept as low as possible though reliability must be of a high order, is in livestock farming and the rearing of young animals in particular. For instance, piglets are usually weaned at about 3 weeks and are then placed in specially-designed rearing pens, the temperature within which must be kept substantially uniform and in general above the external ambient temperature in order to ensure satisfactory growth and development of the piglets. In the past, it has been common for a stockman to inspect the pens at regular intervals and to make whatever adjustments to the ventilation and heating seem to him necessary in order to ensure that the piglets are kept adequately warm, but not too hot.If however the stockman mis-estimated the requirements or if there is a sudden change in the external ambient conditions (for example sudden clouding over on a sunny day or vice versa), the piglets may have to suffer an unsuitable environment for maybe several hours before the stockman next inspects the pens and makes whatever further adjustments are necessary. Somewhat similar considerations of course apply to other types of livestock farming where the livestock is kept indoors, such as cowsheds and poultry battery houses as well as in other agricultural buildings such as milking parlours and mushroom-growing sheds.

The type of control over the ventilation obviously varies from one installation to another, depending upon the intended use. However, most types of installation include a valve unit which serves to control the admission of fresh air, though other facilities may be provided, such as heaters which may be switched on or off or perhaps to some intermediate setting as well as fans, to assist the introduction of fresh air through the valve arrangement or to recirculate air within the building itself.

So far as the valve unit is concerned, this normally can be set fully closed, fully open, or at any desired intermediate position. In its simplest form, it may comprise no more than a flap cooperable with an opening, means being provided to hold the flap at a desired position. For example, the flap may comprise a portion of the roof of an enclosed box, in the case of pens for rearing piglets. In the case of a poultry house, there may be provided a plurality of roof-mounted ventilators each of which has a valve unit to allow the ingress of fresh air, the valve units each including a rotatable member controlling the opening and closing of apertures to permit or obstruct the flow of fresh air.

Though the above-described valve units may wholly be manually controlled, especially in a case where a large number are linked together it is convenient to provide some form of electrical remote control, in which case a motor or other electrical actuator is suitably provided to effect opening or closing movement of the or each valve unit.Then, if it is desired to introduce some form of automatic control, it is usual to provide a control arrangement which includes some form of sensor for the temperature within the building and a feed-back mechanism coupled to the valve unit, allowing monitoring of the instantaneous position of the valve unit; then, the controller may serve to effect operation of the motor or other actuator to re-set the valve unit at some new position, the motor or other actuator being de-energised when the feed-back arrangement indicates the required new setting thereof has been reached.Clearly such an arrangement is complex, relatively expensive to implement and, in view of the number of parts necessary and the amount of modification necessary if the automatic control is to be fitted to an existing installation, the arrangement is prone to unreliability, especially having regard to the conditions which frequently prevail in agricultural environments. It is therefore a principal object of this invention at least to reduce the problems associated with known forms of control for ventilator assemblies, such as have been described above.

According to this invention, there is provided electronic control apparatus for an electricallyactuated ventilator, which apparatus comprises a sensor adapted to sense an atmospheric parameter and to provide an output dependent thereon, a control circuit responsive to the output from the sensor and arranged to operate switch means for connection to the electrically-actuated ventilator if the sensor output differs from a preselected level by more than a pre-set amount, the control circuit serving to maintain the switch means operated for a determined period on detection of a sensor output differing from the pre-selected level by more than the pre-set amount, whereby an electrically-actuated ventilator connected to the switch means will be operated in the appropriate sense for said determined period on the sensed atmospheric parameter deviating from a required value by more than a pre-set amount.

It will be appreciated that in implementing a ventilation system incorporating an electronic controller of this invention, it is not necessary to provide any form of feedback arrangement from the electrically-actuated ventilator to indicate the instantaneous setting thereof; instead, the control apparatus is arranged to effect operation of the electrically-operated ventilator in the required sense for the determined period and, if the sensed parameter does not then return to the desired value, the control apparatus may serve to cause the electrically-actuated ventilator to be operated again, once more for the determined period. This operation may continue until such time as the sensed parameter reaches the required value.

Ordinarily, the sensed parameter will be temperature, though other parameters could be sensed - for instance, humidity, the level ofinpurities in the atmosphere, or the carbon dioxide or oxygen levels of the atmosphere. However, hereinafter reference will be made exclusively to temperature though it will be understood that this term is intended to encompass such other parameters as may be monitored.

Because in a complete installation the temperature cannot be expected to stabilise immediately after an actuation of the ventilator in the required sense for the determined period, it is greatly preferred for the control apparatus to include delay means connected to inhibit further operation of the switch means for a second period, following a first operation thereof. In this way, if the sensed temperature deviates from the required value by more than a particular amount, the ventilator will be actuated in the appropriate sense and then further operation thereof will be inhibited for the second period to allow time for the temperature to stabilise at a fresh value; if this fresh value at the end of the second determined period is not the desired one, then the ventilator may be operated again, and so on until the required value is reached.It is however advantageous for the control apparatus to be arranged such that if during the second period following a first operation of the switch means the temperature is detected to deviate in the opposite sense from the required value as compared to that deviation which caused the first operation of the switch means, then timing of the second period is cancelled and the switch means is operated to cause actuation of the ventilator for a determined period in the opposite sense to that on the first actuation thereof.

In order to allow optimum adaptability of the control apparatus for many varied situations, it is preferred for the control apparatus to be manually adjustable to allow setting of the desired temperature value (and hence of said pre-selected level within the control apparatus), the pre-set amount by which the sensor output may differ from the pre-selected level, and the determined period of operation of the switch means. For instance, preferred ranges of manual adjustment of these values are respectively 50 to 25 C, 1/20 to 50C and 1 to 10 sec. Moreover, for a case where further operation of the switch means is inhibited for a second determined period following a first operation, the second determined period preferably is manually adjustable over the range of 1 to 10 minutes.

Instead of the determined period being manually pre-set, as described above, for certain applications it is advantageous for the period of operation of the switch means to be variable, but determined by the control apparatus itself, taking into account the amount by which the sensed temperature differs from the required temperature. For example, if the sensed temperature differs greatly from the required temperature, then the control apparatus may determine a relatively long period of operation for the switch means; conversely, a relatively small temperature differential would give rise to the control apparatus determining a relatively short period of operation.

Trials have shown that the most advantageous relationship between the temperature differential (i.e. between sensed and required temperatures) and the period of operation of the switch means is substantially exponential, rather than linear. Such a relationship allows close control of the required temperature to be achieved, notwithstanding rapid changes for instance in the external ambient temperature without the need for the added cost and complication of a position-proportioning feedback control system.

It is preferred for the electronic control apparatus to be arranged also to allow the control of one or more heaters should the sensed temperature fall below the required value by too much, and the control of one or more air boost fans should the sensed temperature rise above the required value by too much.Thus, it is convenient for the control apparatus to include further switch means respectively for connection to the or each heater and to the or each fan, and for the circuit to respond to the sensed temperature in such a way that should the sensed value deviate from the required value by more than twice the amount which causes operation of the switch means for actuation of the ventilator, then the switch means for the or each heater will be operated (if the sensed value is below the required value) or the switch means for the or each fan will be operated (if the sensed value is above the required value).

Though in the foregoing the control apparatus has been described as having a single switch means and operating on a single sensor output, the apparatus may be modified to provide multichannel operation. Thus, there may be a plurality of sensors each having associated therewith a switch means for a ventilator, the apparatus being arranged to step through a sequence of operating on each sensor output in turn, and causing operation of the associated switch means for a determined period, if necessary. For a typical installation, there may be eight sensors and eight switch means, each for connection to a respective electrically actuated ventilator associated with the respective sensor.The control apparatus may then have a scanning arrangement which connects each sensor in turn to allow the comparison of the output thereof with the preselected level, and which also connects each switch means in turn to allow the operation thereof if the sensed and pre-selected levels differ by more than the pre-set amount.

This invention extends to a ventilation installation comprising the combination of at least one electrically-actuated ventilator including an electrically-operated actuator, and electronic control apparatus of this invention as described above, with the switch means of the control apparatus connected to the actuator so that the actuator is energised to effect adjustment of the ventilator in the appropriate sense on operation of the switch means. Preferably the installation also includes both at least one heater and at least one air circulation boost fan so as to allow greater control of the environment, the or each heater and fan also being controlled by the control apparatus depending on whether the sensed temperature is respectively lower than or higher than the required value, by more than a particular amount.

By way of example only, two specific embodiments of control apparatus constructed in accordance with this invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a block diagram of the first embodiment of control apparatus, which is arranged to control an electrically-actuated ventilator as well as at least one heater and at least one boost fan; Figure 2 is a diagram showing the operation of the apparatus of Figure 1; and Figure 3 is a block diagram of the second embodiment of control apparatus, arranged to allow the monitoring of eight sensors and the control of eight associated ventilators.

Referring initially to Figure 1, a negativetemperature-coefficient thermistor 10 is connected to a temperature-measuring bridge circuit 1 the output of which is fed through an amplifier 12 to four comparators 13 to 16. The bridge circuit 11 has a manually-adjustable control 1 7 by means of which the balancing point of the bridge can be adjusted; the output from the bridge is thus indicative both of the deviation of the sensed temperature from the value set on control 1 7 as well as the sense of that deviation.

The four comparators 13 to 16 are set up such that comparators 13 and 14 respond when the sensed temperature is higher than the preselected temperature by pre-set amounts, whereas comparators 1 5 and 1 6 respond when the sensed temperature is lower than the preselected temperature by pre-set amounts.

Comparators 14 and 1 5 are arranged to provide outputs when the sensed temperature deviates by 1 OC, respectively above and below the set value, whereas comparators 1 3 and 1 6 are arranged to provide outputs when the sensed temperature deviates by 20C, respectively above and below the set value.

The outputs of the comparators 14 and 1 5 are supplied to a 2-input OR-gate 18, the output of which triggers both an adjustable actuator-run timer 1 9 and an adjustable actuator-re-run delay -timer 20. The actuator-run timer 1 9 provides an output pulse of the required duration to two 2 input AND-gates 21 and 22, the other inputs of which are respectively connected to the comparators 14 and 1 5. In this way, an output will be provided from AND-gate 21 or AND-gate 22 only when an output is present from the associated comparator 14 or 1 5 and an output pulse is present from the actuator-run timer 1 9.

The timers 19 and 20 are arranged so that when the OR-gate 1 8 provides an output to trigger the actuator-run timer 19, the re-run delay timer 20 also is triggered, the output therefrom serving to inhibit further triggering of the actuator-run timer 1 9 for the period of delay provided by the delay timer 20; thereafter if there is stiil an output from the OR-gate 1 8 the actuator-run timer 1 9 may be triggered again - but so also will be delay timer 20, thus preventing a yet further triggering of the actuator-run timer 19 until the end of yet another period of delay.

Four relays 23 to 26 are associated respectively with the comparators 1 3 to 16, relay 23 having switch contacts for connection to a boost fan (not shown), relay 24 having switch contacts for connection to the actuator of a ventilator (not shown) to effect opening thereof, relay 25 having switch contacts for connection to the actuator of the ventilator to effect closing thereof, and relay 26 having switch contacts for connection to a heater (not shown). Lines 27 and 28 are provided to over-ride outputs from the AND-gates 21 and 22 respectively, such that an output from comparator 13 will hold both relays 23 and 24 closed irrespective of the state of AND-gate 21, and an output from comparator 1 6 will hold both relays 25 and 26 closed, irrespective of the state of AND-gate 22.

The operation of the above-described control apparatus will now be described, referring additionally to Figure 2. Should the temperature sensed by the N.T.C. thermistor 10 deviate by at least 1 OC from the required value set on control 17, comparator 14 or 1 5 will trigger, depending upon the sense of the deviation. Thus, if the deviation is 1 OC above the required value, comparator 14 will provide an output triggering both timers 1 9 and 20 and the output from the actuator-run timer 19 in conjunction with the output from comparator 14 will cause the relay 24 to close, for the pre-determined period of the run timer 1 9 - which is adjustable typically over the range of from 1 to 10 seconds. The actuator connected to the relay 24 is thus energised for the pre-determined period to adjust the ventilator to a more open setting. At the end of the predetermined period, the relay 24 will open even though the deviation of the sensed temperature will probably still cause the comparator 14 to provide an output: the relay 24 opens because the re-run delay timer 20 inhibits further triggering of the actuator-run timer 1 9. The period of such inhibition is adjustable typically over the range of from 1 to 10 minutes.If, at the end of that inhibition period the sensed temperature stilldeviates by an amount sufficient for the comparator 14 to continue to provide an output, then the re-run timer 1 9 will again be triggered once -more, to cause the relay 24 to close again for the pre-determined period, thus opening the ventilator yet more. It will be appreciated that the amount by which the ventilator is opened in each pre-determined period is proportional to the length of that period and of course dependent upon the physical construction of the ventilator and its actuator.

In a manner similar to that described above, relay 25 is closed on the comparator 1 5 detecting a deviation from the sensed value of 1 C or more below the required value.

Should the sensed temperature deviate from the required value by 20C or more, then comparator 1 3 provides an output to close relay 23 if the sensed temperature is above that required, whereas comparator 16 provides an output to close relay 26 if the sensed temperature is below that required. The hysteresis of both comparators 1 3 and 1 6 is such that the associated relays remain closed until such time as the deviation of the sensed value falls back to 1 OC from the required value. At the same time as relay 23 or 26 is closed, an output on line 27 or 28 causes relay 24 or 25 also to close.Because relay 24 or 25 is held closed continuously throughout the period that comparator 13 or 16 respectively provides an output, the actuator of the ventilator is caused to run in the appropriate sense to set the ventilator either at the extreme open or the extreme closed position -- at which setting the actuator is shut down by limit switches within the ventilator itself, notwithstanding the continued closure of the contacts of relays 24 or 25. Once the deviation of the sensed temperature returns to within 1 C of the required value, then the override on line 27 or 28 is removed and the boost fan or the heater is turned off; control of the ventilator actuator then returns to comparators 14 or 1 5.

Figure 3 shows a control apparatus arranged to allow the monitoring of eight separate sensors for instance disposed one in each of eight animal pens or one in each of eight separate zones of a livestock house - and the control of eight separate ventilators (or groups of ventilators) associated one with each sensor. Illustrated in Figure 3 are the eight sensors 30 and the eight motors 31 of the electrically-actuated ventilators, which sensors 30 and motors 31 are connected in pairs to eight switching modules 32, each conveniently arranged as a plug-in unit of the control circuit to allow the circuit to be adapted to a particular control requirement.

Within the control circuit itself, there is provided a scanner 33 having eight 'enable' outputs each of which is associated with one of the modules 32 respectively, and each of which is rendered active in turn, so as to cause each module in turn to be connected to the main part of the control apparatus. The scanner 33 also has eight 'enable' switches 34, so as to allow any one of the eight modules 32 to be switched into or out of the scanning sequence. The scanner 33 drives a display 35, on which is displayed the number of the module 32 for the time being connected to the main part of the control circuit.

When a sensor 30 connected by an 'enable' output from the scanner, the sensor is arranged to be connected into a bridge 36, the output of which is fed to one input of a comparator 37. The other input of the comparator 37 is fed with D.C.

signal from a sat-point adjuster 38, such that the magnitude and polarity of the output of the comparator 37 depends on the relative values of the inputs to the comparator, derived from the bridge 36 and the set-point adjuster 38. A display device 39 for temperature is provided, which is driven by an analogue-to-digital converter 40, the input to which may be selected as either the output of the bridge 36, or the output of the setpoint adjuster 38.

The output of the comparator 37 is illustrated at 'A' and is fed to a dead band detector 41, arranged to provide an output on line 42 whenever the sensed temperature is at least C below the required value, and an output on line 43 whenever the temperature is at least C above the required value. Line 42 is connected to one input of a first two-input AND-gate 44 and line 43 to one input of a second two-input ANDgate 45. The other inputs of the two AND-gates 44 and 45 are connected together and are driven by a second comparator 46, one input of which is connected to the output of the first comparator 37 through a first diode 47 and through an inverter 48 and second diode 49. In this way, the waveform supplied to the second comparator 46 is as shown at 'B'.In the second comparator 46, the waveform 'B' is compared with a ramp waveform 'C', of substantially exponential form, produced by a ramp generator 50. The ramp generator 50 is re-set each time the scanner 33 steps to enable another output line.

The above-described control circuit is arranged such that provided there is an output from the bridge 36 indicative of a temperature difference (either above or below) from the required temperature, one of the two lines 42 or 43 will go high, to impress an input on one of the two ANDgates 44 or 45. The modulus of the output of the first comparator 37 is applied to the second comparator 46, and the arrangement is such that the output of the second comparator is high so long as the modulus of the first comparator output is higher than the instantaneous output from the ramp generator 50.Thus, there is a high output at the appropriate AND-gate 44 or 45 selected by the dead band detector 41, until such time as the output of the ramp generator 50 becomes equal to the signal applied to the other input of the second comparator 46, at which point the output of the respective AND-gate 44 or 45 goes low.

Each AND-gate 44 and 45 drives an associated relay 51 and 52 respectively, which relays are connected sequentially to the switching modules 32 on operation of the scanner 33, in order to cause operation in the appropriate sense of the ventilator motor 31 connected to that switching module 32 which is brought into the circuit for the time being by the scanner 33.

It will be appreciated that in the foregoing control apparatus, there is a form of "timeproportioning", by means of which relay 51 or 52 is closed for a period dependent upon a sensed temperature differential from a required value.

The particular relay 51 or 52 which is energised depends upon whether the sensed temperature is above or below the required value, such that the motor caused to operate on closing of the relay 51 or 52 will be driven in the appropriate sense to effect the required control of the associated ventilator.

Claims

1. Electronic control apparatus for an electrically-actuated ventilator, which apparatus comprises a sensor adapted to sense an atmospheric parameter and to provide an output dependent thereon, a control circuit responsive to the output from the sensor and arranged to operate switch means for connection to the electrically-actuated ventilator if the sensor output differs from a pre-selected level by more than a pre-set amount, the control circuit serving to maintain the switch means operated for a determined period on detection of a sensbr output differing from the pre-selected level by more than the pre-set amount, whereby an electricallyactuated ventilator connected to the switch means will be operated in the appropriate sense for said determined period on the sensed atmospheric parameter deviating from a required value by more than a pre-set amount.

2. Control apparatus according to claim 1, wherein the sensor is adapted to sense temperature, and to provide an output dependent thereon.

3. Control apparatus according to claim 1 or claim 2, wherein delay means are provided to inhibit further operation of the switch means for a second period following a first operation thereof.

4. Control apparatus according to claim 3, wherein means are provided to cancel timing of the second period and to operate the switch means for the determined period in the opposite sense to that on the first actuation thereof, if during the second period following a first operation of the switch means the temperature is detected to deviate in the opposite sense from the required value as compared to that deviation which caused the first operation of the switch means.

5. Control apparatus according to any of the preceding claims, wherein means are provided to allow manual adjustment thereof, to allow setting of the desired temperature value (and hence of said pre-selected level within the control apparatus), the pre-set amount by which the sensor output may differ from the pre-selected level, and the determined period of operation of the switch means.

6. Control apparatus according to claim 5, wherein the ranges of manual adjustment of'the said values are respectively 5 to 25CC, 1 to 5"C and 1 to 10 sec.

7. Control apparatus according to claim 3 or any claim appendent thereto, wherein the second period during which further operation of the switch means is inhibited following a first operation thereof is manually adjustable over the range of 1 to 10 minutes.

8. Control apparatus according to any of claims 1 to 4 wherein the period of operation of the switch means is variable but is determined by the control apparatus itself, taking into account the amount by which the sensed temperature differs from the required temperature.

9. Control apparatus according to claim 8, wherein apparatus is arranged such that if the sensed temperature differs greatly from the required temperature, then the control apparatus determines a relatively long period of operation for the switch means, whereas a relatively small temperature differential gives rise to a relatively short period of operation being determined.

10. Control apparatus according to claim 9, wherein the relationship between the sensed and required temperature and the period of operation of the switch means is substantially exponential.

11. Control apparatus according to any of the preceding claims, wherein means are provided to allow the control of one or more heaters should the sensed temperature fall below the required value by more than a pre-set amount.

1 2. Control apparatus according to any of the preceding claims, wherein means are provided to allow the control of one or more air boost fans should the sensed temperature rise above the require value by more than a pre-set amount.

1 3. Control apparatus according to claim 11 and claim 12 wherein the control apparatus includes further switch means respectively for connection to the or each heater and to the or each fan, and means responsive-to the sensed temperature in such a way that should the sensed value deviate from the required value by more than twice the amount which causes operation of the switch means for actuation of the ventilator, then the switch means for the or each heater will be operated (if the sensed value is below the required value) or the switch means for the or each fan will be operated (if the sensed value is above the required value).

1 4. Control apparatus according to any of the preceding claims, wherein there is a plurality of sensors each having associated therewith a switch means for a ventilator, the apparatus being arranged to step through a sequence of operating in turn on each sensor output, and causing operation of the associated switch means for a determined period if necessary.

1 5. Control apparatus according to claim 14, wherein there is a scanning arrangement which connects each sensor in turn to allow the comparison of the output thereof with the pre selected level, and which also connects each - switch means in turn to allow the operation thereof if the sensed and pre-selected levels differ by more than the pre-set amount.

1 6. Electronic control apparatus substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or in Figure 3 of the accompanying drawings.

1 7. A ventilation installation comprising the combination of an electrically-actuated ventilator including an electrically-operated actuator, and electronic control apparatus according to any of the preceding claims with the switch means of the control apparatus connected to the actuator so that the actuator is energised to effect adjustment of the ventilator in the appropriate sense on operation of the switch means.

1 8. A ventilation installation according to claim 17, wherein there are at least one heater and at least one air circulation boost fan so as to allow greater control of the environment, the or each heater and fan also being controlled by the control apparatus depending on whether the sensed temperature is respectively lower than or higher than the required value, by more than a particular amount.