Uson SPRINT LC, Owner'S Manual

Page: 184 / 208

Downstream Sensing
In some test parts, the crack (pressure change) is so gradual or low in
magnitude that the sensor can’t detect the pressure change. This isn’t a
fault of the sensor, rather the placement of the sensor in the test circuit
becomes an issue. Being upstream from the product, the normal sensor is
subjected to constant makeup air.
To test products that open slowly or merely “weep,” Uson can provide a
separate sensor used downstream from the cracking device to detect very
slight pressure or flow changes. In this arrangement, the downstream
sensor measures the small pressure or flow variations caused by changes
in the product being tested. This arrangement works if downstream air can
be routed back to Sprint LC.
The Crack Event
In a crack test Sprint LC is equipped with two sensors. The standard
transducer measures the pressure rise being feed to the test part, on the
upstream side. The second sensor is the downstream sensor. The crack
event is a change in pressure or flow on the downstream side of the test
part. This downstream sensor can be either a pressure or flow sensor.
Two measured values are associated with an event value—
X
The peak pressure attained. (Upstream side)
X
The amount of pressure or flow rise. (Downstream side)
Both sensors are monitored at the same time. To register as a pass, the
upstream peak pressure must be within the min and max crack window
AND the downstream pressure or flow must exceed the event setting. For
example, if the event is set at 0.05 psig, the down stream pressure is
monitored till it increases more than 0.05 psig. At that time: the peak
upstream pressure must fall within the minimum and maximum crack
settings for the test to pass.
Appendix 24