Agricultural fan control system

Agricultural fan control system for controlling operation of fan in an agricultural installation including a thermostat temperature control, a manual constant speed adjustment temperature control, and an automatic variable fan speed with a minimum temperature setting. The control system is fully enclosed in a dustproof, waterproof box with a spring-loaded cover for use in a barn. The sensor unit can be remote from the control unit, and accounts for a seven-degree fahrenheit temperature rise on modulating setting from minimum to maximum c.f.m. Voltage curve of the electrical system is inverted and slower so that there is a slower fan speed increase on the first five degrees than on the last two degrees temperature-wise. The system includes a minimum setting allowing for a constant minimum air movement while including a manual setting for maintaining constant maximum air movement. The c.f.m. to heat requirements is adjusted accordingly between 45.degree.-110.degree. F. The system will handle one or more fan units operating on either 110 or 220 line voltage VAC.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to an agricultural electrical control 
system, and, more particularly, pertains to an agricultural fan control 
system where the fans are utilized in barns or other agricultural 
buildings. 
2. Description of the Prior Art 
The prior art agricultural fan control systems have suffered from two major 
deficiencies. The first deficiency is that the systems were never intended 
to handle more than one fan motor unit and therefore were strictly limited 
in application in a large agricultural building typical of that found on 
the farms. The units were only intended to handle a single unit fan 
assembly, which was less than desirable considering the fact that 
sufficient air can sometimes not be moved by one fan assembly, the units 
were not flexible enough or modulated to control building temperature, and 
the systems would not accurately maintain a desired temperature range or 
desired movement of cubic feet of air through the agricultural building. 
A second major deficiency of the prior art systems was that the systems 
were not protected against the elements of the environment, such as dust 
and moisture, and were forever requiring maintenance and repair which was 
less than desirable for the typical farmer, such as the midwestern farmer 
with little electrical or agri-electrical background. 
Some of the deficiencies with the other units were that a specialized 
installation was required which was not available to the typical farmer or 
agricultural environment, the expense of the installation was prohibitive 
to the facility such as the barn and the individual, as the farmer, and 
the system while sometimes having all of the "bells and whistles" failed 
in the end to truly modulate the fan or fans in maintaining a desired 
temperature and moving a desired amount of air through the agricultural 
building. 
The present invention overcomes the disadvantages of the prior art by 
providing an economical, totally enclosed agricultural fan control system 
which passes all national electrical codes and provides three types of 
temperature control through a thermostat, manual control, and automatic 
variable speed with minimum setting. 
SUMMARY OF THE INVENTION 
The general purpose of the present invention is to provide an agricultural 
fan control system having three types of temperature control of 
thermostatic setting, manual constant speed adjustments, and automatic 
variable speed with a minimum setting for an operating range of 45.degree. 
to 110.degree. F. and for handling one or more fan units on either 110 or 
220 line voltage. The unit is totally enclosed in a dustproof, waterproof 
box providing that an entire agricultural building such as a barn can be 
washed down without affecting in any way the agricultural fan control 
system. 
According to one embodiment of the present invention, there is provided an 
agricultural fan control system including a modulator electrical unit with 
a low-voltage control system, a high-voltage regulator circuit connected 
to a motor, and an LED-photocell optical control circuit coupling the 
low-voltage control circuit to the high-voltage power circuit, a 
thermister sensor connected in the low-voltage circuit, and at least one 
or a plurality of fan units connected across a phased fired triac in the 
high-voltage circuit, a speed adjustment in the high-voltage circuit, the 
temperature sensor positioned in the environment of the agricultural 
building adjacent to the electrical control system, the one or more than 
one fan unit positioned in the agricultural building, the modulator 
electrical control circuit of the agricultural fan control system 
including a thermostat switch and a speed adjustment switch, the modulator 
electrical control circuit including provisions for thermostatic 
temperature control, manual constant speed adjustment for the fan, an 
automatic variable speed with a minimum temperature sensing, whereby the 
system provides for a slower fan speed increase on the first five degrees 
on temperature than on the last two degrees of temperature rise 
fahrenheit, provides a minimum setting which allows a constant minimum air 
movement, and has a manual setting for maintaining the constant maximum 
cubic feet per minute of air movement thereby providing an operating range 
of 45.degree.-110.degree. F. 
One significant aspect and feature of the present invention is an 
agricultural fan control system, trademarked as "MODU-STAT", providing 
three types of temperature control of thermostatic, manual constant speed 
adjustment of a fan, and automatic variable speed adjustment of the fan 
with minimum setting. 
Another significant aspect and feature of the present invention is 
providing a slower fan speed increase on the first five degrees of 
temperature than on the last two degrees of temperature rise fahrenheit. 
This has a great advantage where supplementary heat is needed so that the 
fan does not waste heat source and waste fuel. 
A further significant aspect and feature of the present invention is a 
manual setting of the system so that a constant maximum air movement can 
be maintained, which is very important where auxiliary heat such as 
brooder stoves is used. In this way air movement can be matched to heat 
requirements. 
An additional significant aspect and feature of the present invention is a 
broad temperature range of 45.degree.-110.degree. F. 
Having thus described one embodiment of the present invention, it is a 
principal object hereof to provide an agricultural fan control system for 
use in an agricultural environment, such as a barn, having one or more 
fans for maintaining temperature as well as air flow through the barn. 
Another object of the present invention is to provide a fan control which 
is totally enclosed in a waterproof, dustproof box so that a barn can be 
washed down without affecting the agri-electronics. 
A further object of the present invention is an agricultural fan control 
system which handles one or more fan units, operates on line voltage of 
either 110 or 220 VAC, and providing for external wire hookup with 
color-coded wires which can be installed by the average individual farmer, 
not requiring a professional electrician or agri-electronic expert.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a plan view of an agricultural fan control system 10 
including an electrical modulator control housing 12, a sensor 14, and 
load fan motors 16 and 18 in a barn 20. A line cord 22 connects to the 
modulator electrical control housing 12 which is waterproof and dustproof. 
FIG. 2 illustrates a front view of the modulator electrical control box 12 
with a flip cover 26 at hinges 24 flipped in an upright position. A panel 
28 supports a fan speed switch 30, a temperature switch 32, and positions 
behind an outer cover 34. A plurality of color-coded wires 36 extend out 
from the bottom of a junction 38. The box 12 can be die-cast, the panel 28 
can be screwed on and the cover 26 can be spring-hinged to encompass the 
outer cover 34 with a gasket 40 therebetween. 
FIG. 3 illustrates an electrical circuit schematic of the agricultural fan 
control system 10 where the circuit 50 includes power supply components 
52-58 including a voltage dropping resistor 52, a rectifier 54, the zener 
diode 56, and a filter capacitor 58. These components maintain voltage 
regulation. Resistors 60 and 62 are voltage dividers operating in 
conjunction with the operational amplifier 66 with feedback resistors 64 
and 68. Resistor 70 is an input limiting resistor. Switch 72 is coupled to 
the speed variable resistor 90 which is a speed control 30. Resistor 74 
connects to the switch 72 and resistor 68 and other components, as 
illustrated. Resistor 76 is a bridge resister and variable bridge resistor 
77 connects accordingly. The thermistor 78 is the temperature sensor 14. 
An LED 80 connects at the top side of the low-voltage portion of the 
circuit to a photocell 82 which is on the bottom side of the high-voltage 
portion of the control circuit. A phase control resistor 84, a phase 
control control capacitor 86, a phase control capacitor 88, and a phase 
control variable resistor which is the fan control 30 connect accordingly 
in the portion of the high-voltage side of the power circuit. A gate 
current line resistor 92 connects to a diac 94 which connects to the gate 
of a triac 96. The commutating capacitor 98 which limits peak transients 
during synchronized switching connects in series with a commutating 
network resistor 100 across the triac 96. A motor 102 representing a fan 
or a plurality of fans connects between the triac and one side 104 of the 
line voltage 22. 
MODE OF OPERATION 
In the thermostat mode, the switch 72 is off. The difference on the inputs 
of the op-amp 66 is amplified by the feedback of the ratios of resistors 
64, 62, and 60 where pin 2 is the inverting input of op-amp 66. A resistor 
bridge is formed by resistors 60, 62, 76, 77, and 78 where the imbalance 
of the bridge is amplified by the op-amp 66 to turn on LED 80 which is 
proportional to the balance. The photocell 82 becomes a variable resistor 
as a function of the bridge imbalance where the actual photo effect takes 
place and isolates the low-voltage sensitive circuit from the high-voltage 
power circuit. 
In the manual constant speed adjustment, the variable resistor 90 
determines the speed with the switch 72 on, the resistor 74 is connected 
which allows the operational amplifier 66 to control the LED 80. The 
switch 72 is open, the LED 80 is now completely controlled by the op-amp 
66, capacitor 71, resistors 69, 70, 76, and 77, and thermistor 78. If the 
inverting input to the op-amp is negative, the output will swing positive 
and the LED will go into full illumination, resulting in minimum 
resistance of the photocell 82 affecting the phase shift of the network of 
capacitor 86 and parallel with capacitor 88. If the inverting input is 
positive, the output will swing negative and the LED will be at zero 
illumination, which makes the photocell 82 go to maximum resistance. 
The constant speed determined by the phase relationship of the trigger 
circuit comprising the capacitor 88 and the variable resistor 90 where the 
value of the variable resistor determines instantaneous voltage between 
point A of the RC network and the applied power line voltage. If the 
instantaneous power line voltage exceeds the value applied at the gate of 
the triac 96, the phase displacement network turns the triac on. 
In manual operation or to set minimum hand speed, the temperature lower 
knob is turned clockwise as far as it will go and then the upper knob for 
fan speed is set for the desired fan speed. In thermostat operation, the 
upper knob is turned to T and the lower knob is set to the desired 
temperature for turning the fan on and off. 
In automatic operation, the lower temperature knob is turned to the desired 
temperature. The fan will modulate based upon temperature but will not go 
below minimum speed on an upper knob setting. The voltage curve for the 
modulating setting for fan operation for air flow of minimum to maximum 
cubic feet per minute is based on a 7.degree. temperature rise fahrenheit, 
by way of example and for purposes of illustration only, and not to be 
considered as limiting of the present invention. The voltage curve is 
inverted and slower so that there is a slower fan speed increase on the 
first five degrees than the last two degrees of the temperature rise 
fahrenheit. This has its greatest advantage where supplementary heat is 
needed, so the fan does not work against the heat source and waste fuel. 
The minimum setting allows a constant minimum air movement. 
The fan motors are powered at a slower speed over the first five degrees of 
temperature rise and at a faster speed for the last two degrees of 
temperature rise fahrenheit. As the temperature increases over the 
predetermined set point, the speed increases and is controlled by the 
operational amplifier which fires the triac. The variable resistor sets 
the fan speed while the Wheatstone bridge sets the temperature through the 
variable resistor. 
The fan speed is controlled through the brilliance of the photocell which 
goes from a dark condition to maximum brilliance for the first five 
degrees fahrenheit, and then the remainder of the curve is determined by 
the fixed resistor 69 for sweeping through the remainder of the curve. 
The operation of the fan is directly proportional to the inverting log 
emitter operational amplifier for firing the triac and is dependent upon 
increasing brilliance function of the LED and photocell combination for 
increasing the speed of the fan. 
Various modifications can be made to the present invention without 
departing from the apparent scope thereof. The temperature ranges can be 
varied accordingly, depending upon the particular climates of operation or 
the particular conditions for agricultural usage.