Control System for the Ventilating Means in a Poultry Building or the Like

This invention relates to a control system for opening normally closed ventilating means in a poultry building or the like in response to power failure of the building ventilating system.

U.S. Pat. No. 3,429,298 issued Feb. 25, 1969 discloses a poultry house and an associated curtain raiser which includes an electric motor controlled by a relay, a thermostat and a timer to operate the building curtains through a system of controlled cables.

U.S. Pat. No. 4,605,162 issued Aug. 12, 1986 discloses a bimetal strip mounted to a mechanical arm and inserted into a power resistor used as a heater. In arrangements of this type, the time delay following power failure cannot be determined with any degree of accuracy and the energy required is substantial.

According to this invention in one form the operating handle of a winch used to operate building curtains is arranged with its handle physically connected with the armature of an electromagnet. The electromagnet is energized from a source of direct electric current through circuit elements including a MOSFET operated as a switch. The gate of the MOSFET is arranged in parallel with a resistor and a capacitor so that upon the occurrence of power failure discharge of the capacitor through the resistor the drain to source resistance of the MOSFET is increased. At a predetermined point proportional to the product of the resistance of the resistor and the capacitance of the capacitor the MOSFET is switched off to deenergize the electromagnet and to release its armature which in turn allows the winch to rotate and to open the curtains.

In the drawings, FIG. 1 is a schematic representation of the elements of the invention which control a winch and its associated cable arranged to operate building curtains not shown;

FIGS. 2a, 2b and 2c are enlarged separate views of an armature which is secured to the winch handle and is controlled by an electromagnetic device; and

FIG. 3 is a system wiring diagram showing the details of the electric components provided according to this invention.

In the drawings the numeral 1 designates a power module which is a commercially available power unit such as Technical Device P/N AD-0630 supplied by Technical Devices, Inc. having a place of business at 8529 North Dixie Drive, Dayton, Ohio 45414. These units require only two watts of power for proper operation. Power module 1 may be energized from a wall outlet either from a source 1a of 120 volts AC or from a source 1b of 240 volts AC. In either event the output is 6 volts direct current. As shown in FIGS. 1 and 3, monitor unit 2 is energized through conductors 3 from power module 1. Monitor unit 1c provides the control functions necessary and is identified as P/N 691 built by T&M Inc. located at P.O. Box 1, Young Harris, Ga. 30582. An armature 4 is interconnected with crank handle 5a of winch 5. The armature 4 is held in position immediately adjacent the electromagnet 6 when that magnet is energized. When current to the electromagnet 6 is interrupted, the armature 4 is released and the winch handle rotates thereby to relax the tension on the curtain control cable 7 and to allow the associated curtains to open as is well known. If desired, several electromagnets could be connected in parallel and their associated armatures would drop out at about the same time. Ordinarily only one electromagnet is required.

Under normal conditions with the ventilating means closed, the electromagnetic device 6 is energized by current from power module 1 through conductors 3 and 8, diode 9, the source to drain elements of MOSFET M, and conductor 10. Conduction through MOSFET M is controlled by gate 11.

During normal operation, the capacitor 12 is charged from conductor 8 through diode 13 resistor 14 and conductor 15. The capacitor 12 and resistor 16 are connected in parallel and upon occurrence of a power failure, capacitor 12 begins to discharge through resistor 16. Since the discharge rate of capacitor 16 is proportional to the product of the resistance of resistor 16 and the capacitance of capacitor 12, the time required for discharge down through the threshold of the MOSFET M is readily determined. When the capacitor 12 is discharged to threshold, the MOSFET drain to source resistance increases and reduces current through the electromagnet 6. At a predetermined point, the MOSFET switch is off and the current through the electromagnetic device 6 is reduced and the magnetic field is reduced. When the magnetic field strength is no longer sufficient to maintain the armature 4 in position of control by the electromagnetic device 6, the armature is released and then is free to rotate with the handle 5a of the winch 5. Tension on cable 7 is reduced and the curtains fall to open the building windows.

The zener diode 17 is inserted into the circuit for limiting spike voltage at the gate 11 of the MOSFET.

The capacitor 18 provides for filtering of the unregulated full wave rectified output from the power module 1.

The battery 19 maintains energization of the electromagnet 6 during the time delay period determined on the basis of the values of resistor 16 and capacitor 12.

From the above description, it is apparent that there are no cables to become entangled because there are no cables between the armature 4 and the electromagnetic device 6. Also the unit is ideally mounted on a horizontal level to the winch handle which is free to swing out of the path of the winch as it rotates. The components of the structure enclosed by the dotted line box 1c are sealed in epoxy and the electromagnetic coil is coated and sealed so that moisture, dust etc. have no effect on the operational characteristics of the unit.

The voltage across conductors 8 to 10 is 6 volts direct current and the current is 0.30 ampere so that the entire unit requires less than 2 watts of power.

The time delay period is provided so as to preclude operation of the unit in case a temporary loss of power occurs. This time delay is accurately determinable due to the fact that the discharge rate of capacitor 12 through resistor 16 is proportional to the product of the resistance of resistor 16 and the capacitance of capacitor 12. This fact enables the time delay to be predetermined precisely.

According to this invention a reliable, fail safe, low power, antifouling means for activating the mechanical emergency apparatus in the event of an electric power failure is provided.

Also the system requires very low maintenance and is easily reset and requires no replacement of expended parts after each power outage.

The arrangement can instantly reset upon reapplication of power even if such reapplication occurs during the delay time.

The device can be quickly and easily tested without the expense of expendable parts and of time consuming delays.

Also the operation of the unit is effected without any risk that cables could become entangled in the winch handle.

The operating characteristics are not altered by exposure to environmental conditions.

A state of the art channel enhancement mode MOSFET was chosen because of the extremely high gate input impedance (10.sup.12 ohms) which allows a simple RC integrator network when charged to a voltage above threshold to maintain the gate voltage above threshold for a predetermined time which is dependent only upon the product of the resistance of resistor 16 and the capacitance of the capacitor 12.