It is very difficult to make accurate low pressure
measurements (5 inches of H20 to 15 psig) without taking
barometric pressure into consideration. Barometric pressure is not
constant. It is a function of atmospheric conditions. Normal
Barometric pressure will normally change very slowly in the course
of a day. However, barometric pressure inside a facility can
change quickly when an HVAC system cycles on or off, when a door
opens or closes, or a fan turns on or off. Barometric pressure has
a large effect on low pressure differential measurements.
The solution for accurate low pressure measurements is to take
control of the reference side of the pressure sensor or pressure
scanner. There are several things the user can do to control and
minimize Barometric changes. The first thing is to place the
pressure scanner or pressure transducer in a pneumatically benign
location that is not near a fan, room doors, or air conditioning
systems. A good solution would be to connect the reference input to
a static basket, or static bottle, part number 81263-1, to minimize
the potential for measurement errors. This bottle should be mounted
somewhere accessible to the reference side of the pressure sensor,
or pressure scanner. The end result is a quiet barometric immune to
small changes in the room ambient.
For larger facilities where many pressure measurements are made
and multiple static lines may be used, a static basket may be the
preferred choice. Scanivalve Corp offers a pressure static basket,
part number 80893.
