Fluke 6270A - Component Servicing; Pressure Leakage Test (on-board diagnostics)

Pressure Controller/Calibrator
Rear-Panel Manifold Pressure Connections
21
The REF port can be sealed from atmosphere in most applications where the test
times are relatively short. This isolates the port from pressure changes in the
atmosphere and results in very stable pressure measurement and control.
If the test times are relatively long, in addition to connecting the reference ports
together, they should also be connected to a buffer tank with a large volume (size
depends on application). Vent the tank to atmosphere through a small orifice
bleeder valve at the other end of the tank. Shield the entire reference assembly
from rapid fluctuations in air temperature and flow. Set the vent valve
experimentally. In an environment with no temperature change, the vent valve is
closed. In an environment with no pressure fluctuations the vent valve is wide
open. The appropriate setting varies but a good compromise can be found. To
see the variations, connect the reference as discussed and open the test port to
atmosphere. In Measure mode, the Product indicates the variations. A good filter
can be used in place of the valve if it provides nearly the correct restriction of air
flow.
One consideration is that if the reference port is completely sealed from
atmosphere, its pressure changes due to barometric pressure changes or
temperature changes in the environment. If the pressure in the REF port
becomes lower than the barometric pressure, then a vacuum pump needs to be
attached to the EXHAUST port to allow the Product to control down close to
0 psig.
For Products that have a BRM installed, the barometer is tied to the reference
port. When Gauge mode is used, connect the REF port as noted above. When
used in the Absolute mode, if the ambient pressure is not stable, sealing the
reference port from atmosphere improves the control stability of the Product.
VENT Port
The VENT Port ties the internal volume to atmosphere when the Product is
vented.
Note
Leave the VENT port open to atmosphere to ensure proper
operation of the Product.