GB2077958A - Temperature control apparatus for animal houses - Google Patents

Abstract

Apparatus for controlling the temperature of an electrically heated animal house such as a pig creep, wherein the animal house heater (44) is supplied with current only when a triac (42) is rendered conductive by a train of low current pulses (38) fed to its control electrode. The low current pulse train is produced by a pulse generator only when a comparator detects that one of its d.c. inputs, derived from a temperature sensitive thermistor circuit (12) has fallen below a predetermined level represented by the second d.c. input to the comparator, which second input defines a required temperature level when can be preset through a rheostat (24). The trigger pulses for the triac are synchronised with the zero crossing points of the a.c. supply voltage. <IMAGE>

Description

SPECIFICATION Temperature control apparatus for animal houses This invention relates to temperature control apparatus for animal houses such as pig creeps.

In pig breeding and rearing, it is common practice to install in a piggery, by the side of the sow's pen, a small house for accommodating the piglets. This house has one or more passages open at one end, into which the piglets are attracted by a roof light, and the temperature within the house is controlled by an electric heater just below the roof to keep the piglets adequately warm. Such a house is known as a pig creep.

The electric heater is usually of the infra-red kind, and it is known to integrate with the heater a thermostatic control incorporating a bimetallic switch, the complete unit being accessible through an aperture in the roof. Such a known arrangement is disadvantageous, firstly in allowing heat to escape through the apertured roof, and secondly in wasting electricity because the thermostatic control is invariably relatively insensitive and, in order to ensure that the house is kept sufficiently warm at all times, the thermostat must be set to maintain an average temperature well above the minimum temperature which is necessary.

It is an object of this invention to provide improved temperature control apparatus for animal houses, especially pig creeps, in which the disadvantages of the known integrated heater unit are substantially minimised or avoided.

According to the invention, there is provided apparatus for controlling the temperature of an animal house such as a pig creep by switching an electrical heater on and off in accordance with variation in environmental temperature below and above an adjustable preset temperature level, said apparatus comprising an electrical control circuit which comprises:: a) means for adjustably presetting a reference voltage representative of a required temperature level, b) means for producing an operational voltage variable in response to changes in the environmental temperature, c) a comparator for comparing the reference voltage with the operational voltage, d) pulse generating means driven by the comparator for producing a train of low current pulses only when the operational voltage is either greater than or less than the reference voltage, and e) a high current electronic switch connected in a power supply circuit for the heater, which switch has a control element connected to the output of the pulse generating means and is operative to pass a supply current to the heater only when the control element is either fed or not fed with said train of pulses.

Preferably, the train of pulses is produced only when the environmental temperature falls below the required temperature level, the high current electronic switch, such as a triac, only being rendered and maintained conductive when and while the train of pulses is being fed to its control electrode. A current limiting resistor is preferably provided between the output of the pulse generating means and the control electrode of the triac. Such current limiting resistor is preferably adjustable, and conveniently may be capable of adjustment to restrict the current supply to alternate pulses only of the normal train.

The triac is then operative to conduct unidirectionally, and the heater is supplied with only half cycles of the normal a.c. supply, thus effectively halving the normal power rating of the heater. A breakdown resistor may be connected across the heater power supply circuit, which circuit may also supply the lamp conventionally provided in a pig creep, to minimise or preventtriac spikes.

The pulse discriminating means may conveniently be constituted by an a.c. zero voltage level detector of the kind which produces a spike-like pulse each time the voltage level crosses zero. Since a triac cannot be operated directly by such very short period spike-like pulses, a pulse stretcher is incorporated to provide pulses each of sufficient duration properly to trigger the triac to render it conductive for one half cycle of the heater power supply.

The inputs to the comparator are based on a d.c.

power supply, conveniently derived from the heater power supply, e.g. mains supply, by means of rectification and smoothing. The means producing the reference voltage is preferably constituted by a suitably rated thermistor connected in a voltage divider across the d.c. power supply, whilst the means for producing the operational reference voltage is preferably a rheostat connected across said d.c. power supply. The inputs to the comparator, taken from the voltage divider and the rheostat, are preferably shunted by a capacitor which acts to tie the said inputs to a common base level.

In one practical arrangement, the d.c. supply circuit, the comparator and the pulse generating means (zero voltage detector and pulse stretcher) are incorporated in a processor chip. A chip incorporating the necessary circuitry is already currently available. However, whether or not such a chip is employed, or any other suitable chip incorporating a d.c. generating circuit, it may be preferable to provide the d.c. supply separately, e.g. by use of a transformer and rectifier, for reasons of stability and availability of larger current.

It is envisaged that the control apparatus will be housed in a casing which constitutes a control unit to be fixed to the outside of the animal house, possibly in a position remote from but in any case separate from the heater (and light), which will be connected to the control unit through supply leads passing through holes of minimal size in the wall of the house. This avoids the provision of a roof aperture leading to wasted heat. In addition, the control unit constituted by the above-described control apparatus is capable of maintaining the temperature within the house to the required level, which is set by means of the rheostat suitably calibrated for the purpose, within +B degree Centigrade or less.It has been experimentally determined that the control unit of the invention is thereby capable of reducing power consumption by over 50% compared with a conventional, thermostatically controlled, integrated heater.

The accompanying drawing shows one practical arrangement of the temperature control apparatus for an animal house in accordance with the invention.

This arrangement comprises a processor chip 10, for example the chip reference TDAID2K, which incorporates a comparator connected between the terminals marked 4 and 5. The input 5 is fed from a voltage divider 12 consisting of a resistor 14 and a thermistor 1 6,.which voltage divider 12 is connected between the positive and negative lines 18 and 20 of a d.c. power supply. This last mentioned supply is derived directly from the terminals 1 and 8 of the chip 10 when shunted by a smoothing capacitor 22.

The input 4 of the chip 10 is fed from a rheostat 24 which is calibrated to enable a required temperature level in the animal house to be preset. The terminals 4 and 5 of the chip 10 are tied to a common base level by a capacitor 26. The main input to the chip 10 is on the terminal 7, from mains a.c. power supply live line 28 through a resistor 30 and semi-conductor 32. A high value resistor 34 connects terminal 6 of the chip 10 to the a.c. live line 28. Reference 36 denotes the neutral line of the mains supply, to which terminal 1 of the chip is connected.

The chip 10 incorporates a zero voltage level detector and pulse stretcher whereby a train of low current pulses 38 is output from terminal 2 only when the output of the chip comparator indicates a voltage on terminal 5 lower than that on terminal 4 (environmental temperature below preset required temperature). One such pulse is produced for and at each zero crossing of the a.c. input voltage to the chip. The output terminal 2 of the chip 10 is connected through an adjustable (by manufacturer) current limiting resistor 40 to the control electrode of a double triac 42. The triac 42 is connected in series with the animal house heater 44 and a switch 46 which enables the heaterto be switched off altogether when heating is not required, i.e. in warm weather.These series connected components 42,44, 46 are connected across the a.c. power supply 28, 36, with a neon indicator lamp 47 shunted across the heater 44.

The triac 42 is rendered and maintained conductive, thereby to pass current to the heater 44 assuming the switch 46 to be closed, only so long as its control electrode is fed with the train of pulses 38.

When due to operation of the heater 44the tempera- ture in the animal house rises to the preset required level, the comparator causes the train of pulses 38 to be cut-off, whereby the triac 42 is switched off and current is no longer supplied to the heater 44.

It is important to appreciate the importance of triggering the triac 42 by pulses synchronised with the zero crossing levels of the a.c. supply voltage. If the triac is triggered partway through an a.c. supply voltage cycle, radio interference can occur. This disadvantage is wholly avoided with the described arrangement of the invention, and this remains true with adjustment of the current limiter 40, for example to a condition in which alternate pulses of the normal pulse train 38 are eliminated. The capability for such an adjustment enables a nominally high power rated heater 44 to be operated at half po'yver, i.e. as though it is a heater of half the nominally rated power.

The reference 48 denotes a breakdown resistor to short circuit triac spikes, while the reference 50 denotes a mains a.c. supply "on" neon indicator.

The drawing also shows a lamp 52 associated with switch 54 connected across the mains supply 28,36.

Such a lamp 52 will be used in a pig creep to attract the piglets into the temperature controlled house.

Finally, reference 56 denotes a fuse.

Another important advantage of the invention resides in the power capability of the triac 42, which can be as high as 60 or more amps. This is a power capability sufficient for as many as eight or more heaters 44, which can be located in separate houses, e.g. separate pig creeps within a piggery, and which are electrically connected in parallel. The temperatures within the eight or more houses can thus all be controlled simultaneously (provided that the same temperature level is required for all the houses) by a single suitably positioned unit of the control apparatus. In practice this unit will take the form of a casing incorporating all the illustrated circuitry except the heater 44 and lamp 52, with the two on/off switches 46, 54 and the calibrated rheostat 24 accessible on the outside of such casing and the neon indicators 47, 50 visibly mounted thereon.

It is to be appreciated that the above-described arrangement may be modified in various ways within the scope of the invention. In particular, various circuit modifications are possible which nevertheless enable production or absence of a train of pulses responsive to temperature comparison, which train of pulses, when present, is used to switch on a heater-controlling triac.

Claims (1)

1. Apparatus for controlling the temperature of an animal house such as a pig creep by switching an electrical heater on and off in accordance with variation in environmental temperature below and above an adjustable preset temperature level, said apparatus comprising an electrical control circuit which comprises:: a) means for adjustably presetting a reference voltage representative of a required temperature level, b) means for producing an operational voltage variable in response to changes in the environmental temperature, c) a comparator for comparing the reference voltage with the operational voltage, d) pulse generating means driven by the cornparatorfor producing a train of low current pulses only when the operational voltage is either greatertflan or less than the reference voltage, and e) a high current electronic switch connected in a power supply circuit for the heater, the switch having a control element connected to the output of the pulse generating means and being operative to pass a supply current to the heater only when the control element is either fed or not fed with said train of pulses.

2. Apparatus according to claim 1, wherein the trajn of pulses is produced only when the environmental temperature falls below the required temperature level, and the high current electronic switch is rendered and maintained conductive when and while the train of pulses is being supplied to its control element.

3. Apparatus according to claim 1 or claim 2, wherein a current limiting resistor is connected between the output of the pulse generating means and the control element of the high current electronic switch.

4. Apparatus according to claim 3, wherein said current limiting resistor is adjustable.

5. Apparatus according to claim 4, wherein said current limiting resistor is adjustable to restrict the normal train of a low current pulses to pass only alternate pulses to the electronic switch.

6. Apparatus according to any of claims 1 to 5, wherein said high current electronic switch is a triac, with its control electrode connected to the output of the pulse generating means.

7. Apparatus according to claim 6, wherein a breakdown resistor for minimising triac spikes is connected across the heater power supply circuit.

8. Apparatus according to any preceding claim, wherein the pulse generating means comprises an a.c. zero voltage level detector producing a spike pulse each time the voltage level crosses zero.

9. Apparatus according to claim 8 when appendant to claim 6 or claim 7, wherein the pulse generating means also includes a pulse stretcher.

10. Apparatus according to any of claims 1 to 9, wherein the means for producing the operational voltage comprises a thermistor connected in a voltage divider connected across a d.c. power supply.

11. Apparatus according to claim 10, wherein the means for producing the reference voltage comprises a variable resistor connected across the d.c.

power supply.

12. Apparatus according to claim 11, wherein the inputs to the comparator, taken from the voltage divider and the variable resistor, are shunted by a capacitor.

13. Apparatus according to claim 10 or claim 11 or claim 12, wherein the d.c. power supply is obtained by rectification of the heater power supply.

14. Apparatus according to any of claims 1 to 13, in combination with an animal house such as a pig creep having a heater controlled by said apparatus.

15. The combination of claim 14, wherein the control apparatus is contained in a unit located externally of the animal house, with supply leads to the internal heater passing through holes of the minimum necessary in the wall of the house.

16. The combination of claim 14 or claim 15, comprising a single control apparatus and a plurality of animal houses having individual heaters all controlled by the said single control apparatus.

17. The combination of claim 16when appendank to claim 15, wherein a single external unit contains more than one control apparatus each controlling some of said plurality of animal houses.

18. The combination of claim 17, including switches on said unit enabling selective operation of said more than one control apparatus.

19. Temperature control apparatus substantially as hereinbefore described with reference to the accompanying drawings.

New claims or amendments to claims filed on 19 Aug.1981.

Superseded claim 1.

New or amended claim: CLAIMS

1. Apparatus for controlling the temperature of an animal house such as a pig creep by switching an electrical heater on and off in accordance with variation in environmental temperature below and above an adjustable preset temperature level, said apparatus comprising an electrical control circuit which comprises: : a) means for adjustably presetting a reference voltage representative of a required temperature level, b) means for producing an operational voltage variable in response to changes in the environmental temperature, c) a comparator for comparing the reference voltage with the operational voltage, d) pulse generating means driven by the comparatorfor producing a uniform frequency train of low current pulses only when the operational voltage is either greater than or less than the reference voltage, and e) a high current electronic switch connected in a power supply circuit for the heater, the switch having a control element connected to the output of the pulse generating means and being operative to pass a supply current to the heater only when the control element is either fed or not fed with said train of pulses.