group 9 warehouse humidity controller
TRANSCRIPT
Instrumentation and Control System
Group 9
Warehouse Humidity Controller
In some warehouse, it is essential that the relative humidity be maintained above a certain level.
Two good examples are:
1. Warehouse that store explosives
2. Warehouse that store grains
For both of these commodities, it is dangerous to allow the relative humidity to fall below about 50%.If the grain dust gets too dry, spontaneous combustion may occur.
Figure (A) Physical system for maintaining warehouse humidity
Figure (B) The psychrometer detector and water-flow-control circuit
The nickel RTD’s have a resistance of 20kΩ at 60˚F.The dry bulb RTD is placed in a Wheatstone bridge in the R4 position, and the wet bulb RTD is placed in the R3 position. The resistance of the RTD are labeled Rdry
and Rwet , respectively. The left side of the Wheatstone bridge divides the 10-V dc supply evenly, since R1 and R2. The right side will not divide the supply voltage evenly because Rwet will be less than Rdry due to its lower temperature. Therefore the bridge will be unbalanced, with the bridge output voltage furnishing the input signal to op amp 1. This input voltage is identified as Vbridge .
On-Off Control System
This ensures a uniform atmosphere throughout the warehouse , preventing any dry pockets from forming
A continuous stream of air from the storage are sucked into the sampling chamber by a small sampling blower
Air is always pulled rather than pushed
In this system, the temperature detectors are nickel wire RTD’s
The dry bulb is always located nearer to the entry of sampling chamber
In this system, the temperature of the storage area is maintained near 60oF by an independent temperature control system
The relationship between the relative humidity and Vbridge is this: As the relative humidity goes down, the temperature difference between the bulbs becomes greater
As the temperature difference becomes greater, the difference between the Rwet and Rdry also increases, throwing the bridge further out of balance.Therefore , a decrease in relative humidity causes an increase in Vbridge.
Temperature difference=10oF
Group 9 Warehouse Humidity
Controller Alcantara, Christopher D.
Cruz , Eduardo A.
Cruz, Jerome
Del Carmen, Lorenzo
Gabriel, Genesis Jerome T.
Malang, Romeo P.