GB2054904A - A method of and apparatus for controlling the output of a power supply unit - Google Patents

Abstract

Apparatus for controlling the output of a power supply unit comprises a graphical representation 14 of continuously variable relationship which is driven across an array of photocells disposed beneath a slit 7 in a housing 1. The array is illuminated and is obscured by the representation so that the output from the array varies in accordance with the representation as it progresses across the array. This variation is employed to control a triac to correspondingly vary the output from a power supply. <IMAGE>

Description

SPECIFICATION A method of and apparatus for controlling the output of a power supply unit The present invention relates to a method of and apparatus for controlling the output of a power supply unit.

A continuously variable voltage supply is often required in the operation of mains operated electrical equipment, such as an electric furnace heater, electric pumps, electric stirrer motors and mixers, electric filament lamps and electric fans.

According to the present invention, there is provided a device for controlling the power output of an electrical supply in accordance with a known continuously variable relationship comprising a graphical representation of the relationship, control means for controlling the power output from the device in dependence upon the position of the representation and means for producing relative movement between the representation and the control means.

A preferred embodiment of the invention may comprise any one or more of the following advantageous features:- (a) The control means comprises an array of photoreactive elements.

(b) The photoreactive elements of (a) are photo transistors.

(c) The photoreactive elements of (a) are photo resistors.

(d) The control means comprises a triac.

(e) The firing point of the triac is adjusted by means of the photoreactive elements of (a).

(f) The means for producing relative movement comprises a drive motor and the graphical representation is supported on or forms part of a frame which is adapted to be driven with respect to the control means.

In order that the invention may be more clearly understood, one embodiment of the invention will now be described, by way example, with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic plan view of a power supply unit, and Figure 2 shows a circuit diagram of the unit of Figure 1.

Referring to Figure 1, the unit comprises a housing 1 inside which a drive motor and electrical control circuitry are disposed. The top face of the housing supports a fixed guide 2 in which one edge of a frame 3 carrying a transparent plate 4 is adapted to run. The opposite edge of the frame 3 is formed with teeth 5 which mesh with the teeth of a pinion 6 which is connected to the output shaft of the drive motor disposed in the housing 1.

The top face of the housing 1 defines an elongate slit 7. This slit 7 extends at right angles to the direction in which the framed plate 4 is driven by the drive motor. An electrical power supply lead 8 leads into the housing 1 and a power output socket 9 is fitted to the side of the housing. An ON/OFF switch 10 for the supply is provided with a power on neon indicator 11.

A control knob 12 is provided for adjusting the speed of the drive motor and therefore the speed at which the framed plate 4 is driven across the top face of the housing.

The plate 4 supports an opaque control card 1 3 which has an upper periphery 14 which represents the variation with time required of the voltage appearing at the output socket 9. Alternatively the plate 4 itself may be formed with transparent and opaque areas separated by a border 1 4 of the desired form.

The circuitry for controlling the voltage appearing at the output socket 9 is shown in Figure 2. The circuit is fed from the supply lead 8 via the switch 10. A fused spur 20 supplies the drive motor and a lamp 21 which is disposed above the top face of the housing 1. An array of photocells 22 is disposed beneath the slit 7 in the housing 1. This array 22 forms, with the resistor R1 variable resistor VR2 and capacitor C1, a phase change network. This network is connected, via a series connection of a resistor R2 and a diac D, to the gate of triac T and via, a further resistor R to one other terminal of triac T. A series connection of a resistor R3 and capacitor C2 connected between the triac T and the live lead of the power lead 8 protects the triac T from high transient voltages and also acts to suppress interference.A full wave rectifying bridge comprising resistors Rei, R5 and R6 and diodes D1, D2, D3 and D4 is provided to stabilise the triggering voltage of the diac D and improve hysteresis.

In operation of the device the plate 4 is driven at a predetermined speed by the drive motor across the photocell array 22 disposed beneath the slit 7. The number of photocells open the the light emanating from the lamp 21 varies independence upon the form of the periphery 14.

Those cells beneath this periphery receive no light whilst those above it do. The number of photcells irradiated determines the photo-conductive voltage and through the diac D the point in the cycle at which the triac switches on and therefore the voltage available at the output socket 9. The device may be zeroed using the variable resistance VR2 so that maximum voltage is available say when the periphery 14 is at zero, and each photocell is individually adjustable, by means of an associated variable resistor. This individual adjustability enables the output voltage from the array to be set to represent a wide range of mathematical laws. Generally, each photocell variable resistor would be set to be practically equal such that movement of the plate 4 across the housing gives a linear voltage response.For special purpose applications, however, the photocell resistors could be set to give a square law response where the movement across is related to the square of the output voltage. Any other mathematical relationship could equally well be chosen.

It will be appreciated that the above enbodiment has been described by way of example and that many viriations are possible without departing from the invention.

it will also be appreciated that the described device or instrument enables a very wide range of equipment to be controlled. For example, the heat energy from electrical furnace heaters can be varied from zero to a maximum in accordance with the periphery of graph 14. The speed of rotation of electrical motors, pumps, blowers, dryers, and fans can be varied between zero and full speed so that flow rates, for example can be made to follow the graph. The illumination of lamps can be varied to different levels to follow the graph.

Consequently, ultra-violet (U.V.) and infra-red (I.R.) tubes for radiation processes can be graphically controlled.

The opening position from closed to fully open of electrical solenoid control valves can follow the graph so controlling the flow rate of chemical processes.

Claims (14)

1. A device for controlling the power output of an electrical supply in accordance with known continuously variable relationship comprising a graphical representation of the relationship, control means for controlling the power output from the device in dependence upon the provision of the representation and means for producing relative movement between the representation and the control means.

2. A device as claimed in Claim 1, in which the control means comprises an array of photoreactive elements.

3. A device as claimed in Claim 2, in which each element of the array is individually adjustable.

4. A device as claimed in Claim 3, in which each element is provided with an associated variable resistor to provide for the individual adjustment.

5. A device as claimed in Claim 2, 3 or 4, in which the photoreacteve elements are photo transistors.

6. A device as claimed in Claim 2, 3 or 4, in which the photoreactive elements are photo resistors.

7. A device as claimed in any preceding Claim, in which the comtrol means comprises a triac.

8. A device as claimed in Claim 7, when appendant directly or indirectly to Claim 2, in which the firing point of the triac is adjusted by means of the photoreactive elements.

9. A device as claimed in any preceding Claim, in which the means for producing relative movement comprises a drive motor and the graphical representation is supported on or forms part of a frame which is adapted to be driven with respect to the control means.

10. A device as claimed in Claim 9, when appendant directly or indirectly to Claim 2, in which the means for producing relative movement is housed in a housing and the upper face of the housing defines a slit extending at right angles to the direction in which the representation is driven, the array being disposed directly beneath the slit such that, in operation of the device, the representation is progressively driven across the array.

1 A device as claimed in any preceding Claim, in which the means for producing relative movement is speed adjustable.

12. A device for controlling the power output of an electrical supply in accordance with a known continuously variable relationship substantially as hereinbefore described with reference to the accompanying drawings.

13. A method of controlling the power output of an electrical supply in accordance with a known continuously variable relationship including the steps of producing a graphical representation of the variable relationship and moving that graphical representation relative to control means in order to activate the control means to control the power output in accordance with the relationship.

14. A method as claimed in Claim 13, in which the control means comprises an array of photoreactive elements which are illuminated and across which the representation is progressively driven to prevent the illumination reaching the array to an extent proportional to the representation in order to control the power output in accordance with the representation.

1 5. A method of controlling the power output of an electrical supply in accordance with a known continuously variable relationship substantially as hereinbefore described with reference to the accompanying drawings.