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Overview / Design Principle:
This unit is designed to control pneumatically can record two separate temperature variables on a common chart. Relative humidity can be governed through the control of wet and dry bulb temperatures. Two independent control systems in a single case. Humidity and temperature control, output 3-15 psi. Manual reset adjustment with adjustable throttling range 5-25%.
Operation:
The dual RFHAA operates air powered throttling valves regulating the flow of steam, water or gas or actuates other pneumatic devices such as pressure switches or relays. Wet and dry bulbs are recorded when it is used to control temperature and relative humidity.
Two instruments with independent pen arms comprise the control. Pen arms are set at two-hour time differential on a 24 hour chart to prevent interference when recording at or near the same control temperature.
Pen arms move up or down scale in response to the expansion or contraction in the thermal sensing element. As a pen arm enters the throttling range an approaches set point, it changes the effective orifice size in its control mechanism's bleed valve.
The control produces an outpu pressure of 3 to 15 psi, approximately 16 psi input pressure is required to obtain this range. Throttling span is adjustable within the extreme of 5 to 15% of the scale range.
Load arm, inherent in throttling controls, is compensated by a manual reset adjustment.
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