GB2069304A - Improvements relating to incubators - Google Patents

Abstract

An incubator is designed for the eggs to lie in a temperature controlled convection air stream. An air permeable tray (11) is surrounded by a barrier (4) supported within a closed box (1), with spaces between the barrier and the box walls (2), base (9) and top (3). Electrical heating elements (10) outside the barrier create a convection current which passes over the barrier and down through the egg tray. The heating elements are thermistor controlled, with a triac in their A.C. power circuit which reduces the power to alternate half-cycles as the desired temperature is approached, and cuts off the power when it is attained. <IMAGE>

Description

SPECIFICATION Improvements relating to incubators This invention relates to incubators. It is primarily concerned with incubators for hatching out poultry eggs, but there are other applications where a carefully controlled environment is important and to which this invention could be applied.

Egg incubators have to kept within very fine limits of temperature: too high or too low for any length of time can 'kill' the eggs. Thermostats have therefore been in general use for governing electric heating means. However, they are subject to wear and deterioration with time and it is difficult to achieve the very narrow range of temperatures required without the thermostat 'hunting' between on and off. Also, the usual heating means, either a fan heater or radiant elements are not ideal. A fan requires a motor, which is subject to mechanical wear and does not take kindly to repeatedly being switched on and off.With radiant elements, it is difficult to obtain an even distribution of heat, and so while the thermostat may operate at the desired temperature, some of the eggs remote from it may be too hot or too cold, or there may be too big a temperature differential across individual eggs.

It is the aim of this invention to achieve an incubator in which there is good, uniform distribution of heat, reliably and accurately controlled to a set temperature, all without mechanically moving parts.

According to one aspect of the present invention there is provided an incubator comprising a closable container, an air permeable tray, a barrier surrounding the tray and being supported to be substantially clear of the side walls, top and bottom of the container, and heating elements between the barrier and the side walls, top and bottom of the container, and heating elements between the barrier and the side walls of the container, the arrangement being such that when the heating elements are energised a convection current of warm air is generated to surmount the barrier and permeate down through the tray.

The barrier will preferably be double walled, with the heating elements mounted on the outside wall. Thus the tray is largely insulated from conduction heating through the barrier. The heating elements can be controlled to fine limits of temperature as described below.

According to another aspect of the present invention there is provided a temperature controller for electrical heating elements, comprising a resistive bridge network including a thermistor, and electronic switching means responsive to the state of balance of the bridge and including a triac in an A.C. power circuit to the heating elements, the arrangement being such that the triac is on only on alternate half-cycles when the desired temperature is approached, is fully on when the temperature is below a first predetermined limit and is fully off when the temperature is above a second predetermined limit.

Generally the bridge will include a variable resistor of potentiometer for the user to set the desired temperature, and another one for initial calibration.

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 diagrammatic perspective view of an incubator, with parts broken away and removed, Figure 2 is a vertical cross-section of the incubator, and Figure 3 is a circuit diagram of a heating control system for the incubator.

The incubator is housed in a container 1 which is an open-topped rectangular box closable by a lid (not shown), preferably transparent. The side walls 2 of the container have inturned flanges 3 from which is supported a rectangular double-walled barrier 4 of generally U-section. The inner walls 5 of this barrier are slightly higher than the outer walls 6 and at the corners they project even higher, forming angled lugs 7 by which the barrier is supported from the flanges 3. This arrangement provides vents 8. The bottom wall or floor of the barrier 4 is clear of the floor 9 of the container 1, and the outer walls 6 are spaced from the walls 2.

Mounted on the outside of walls 6 are elongated electrical heating elements 10. A tray 11 with a wire mesh, perforated metal or other airpermeable bottom is suspended within the barrier.

In use, eggs placed on the tray, the container is closed and the heaters 10 are energised to create convected currents of air as indicated by the arrows in Figure 2. The eggs are shielded from too direct and thus possibly unbalanced heating, and the movement of air, without mechanical aid, ensures even distribution of heat.

The control of this heat can be achieved by the circuit of Figure 3. When reduced to hardware, it can be housed in a compact box attached to the outside of the container 1, as indicated by 12 in Figure 1. This has a knob 1 3 for setting a desired temperature, with reduction gearing as a precaution against excessive adjustments. A thermistor which senses the temperature will be housed in the container 1. The arrangement of the circuit and its components will be evident from the Figure and will not be desribed in detail.

ThermistorTH and resistor R1 and R2 form a bridge, as do resistors R4 and R5. TransistorT1 is a bridge balance detector and provides drive to transistor T2, which in turn provides gate drive to the triac.

This part of the circuit is operated from 12 volts DC, which is derived from the mains transformer at 1 3.5 volts AC. After rectification by the diodes D1 and D2 and smoothing by capacitor C2, it is reduced to 12 volts by regulator VR. This arrangement allows for main fluctuation.

When power is first applied, the thermistor bridge is out of balance, and so transistors TR1 and TR2 are driven hard on. The gate drive to the triac is above 35mA, and so the triac is hard on for both half cycles of the mains AC, thus supplying full power at 50 Hz to the heaters. This shows on the neon tube. As the incubator warms up and the thermistor temperature approaches the intended operating temperature, transistors T1 and T2 are only partially on and the gate drive to the triac falls below 35mA, although remaining above 1 5mA.

This causes the triac to be off for alternate half cycles, and thus to deliver half power at 25 Hz to the heaters. When the temperature tries to rise above the set limit, both transistors and triac close down, cutting off power to the heaters.

The resistor R2 corresponds to the knob 13, and its adjustment sets the desired operating temperature. The resistor R1 is adjusted initially when calibrating the system.

Claims (9)

1. An incubator comprising a closable container, an air permeable tray, a barrier surrounding the tray and being supported to be substantially clear of the side walls, top and bottom of the container, and heating elements between the barrier and the side walls of the container, the arrangement being such that when the heating elements are energised a convection current of warm air is generated to surmount the barrier and permeate down through the tray.

2. An incubator as claimed in Claim 1, wherein the heating elements are mounted on walls remote from those immediately surrounding the tray.

3. An incubator as claimed in Claim 2, wherein the barrier is double walled, with the heating elements mounted on the outside of the outer walls.

4. An incubator substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

5. A temperature controller for electrical heating elements, comprising a resistive bridge network including a thermistor, and electronic switching means responsive to the state of balance of the bridge and including a triac in an A.C. power circuit to the heating elements, the arrangement being such that the triac is on only' on alternate half-cycles when the desired temperature is approached, is fully on when the temperature is below a first predetermined limit and is fully off when the temperature is above a second predetermined limit.

6. A temperature controller as claimed in Claim 5, wherein the bridge includes a variable resistor or potentiometer for setting the desired temperature.

7. A temperature controller as claimed in Claim 6, wherein the bridge include a further variable resistor or potentiometer for initial calibration.

8. A temperature controller for electrical heating elements substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

9. An incubator as claimed in any one of Claims 1 to 4, equipped with a temperature controller as claimed in any one of Claims 5 to 8.