Page 88
FCO770 Users Guide Issue 1
CALIBRATE FLOW PROCEDURE
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When leaks are displayed as a flow reading rather than differential pressure, the FCO770
measures the leak as a pressure drop and then calculates the flow reading. The calculation
relies on the test volume being known as well as the pressure drop in a given time.
The following calculation can be used to convert between flow specifications and pressure
drop per unit time specifications as follows:
(V + Y) x DP/min = cc/min
101325
Where
V = Volume of test com jig + pipework (in cm
3
)
Y = Internal Volume of leak detector (in cm
3
).
DP/min = Measured differential pressure/minute (in Pascals/min)
101325 = Standard atmospheric pressure in Pascals.
This formula can be transposed to determine the test time and fail level as follows:
D.P. per min = cc/min x 101325
and
D.P. per sec = D.P. per min
V + Y
60
The FCO770 can automatically calculate the volume from a known applied leak. There are
three steps required to calibrate the FCO770 to show leakage in flow units.
1.
Set up a good test item in a leak tight test system.
2.
Set a known leak on the test system.
3.
Calibrate the instrument to display the known leak.
Setting up a Leak Tight System.
♦
Connect a known leak tight test item to the Test Port.
♦
Connect an FCO210 Microcalibrator either to the front panel calibration port (if
fitted) or via a 'tee' in the Test Circuit. Turn the Isolation Valve of the FCO210 to
CLOSE.
♦
Set the Leak Units to cc/min, cc/hr or mm
3
/S as required.
♦
Ensure that the test has the test pressure level, fill and stabilisation times and the
approximate volume set up for the test item connected. Set the test time to a suitable
time to give a stable leak reading; this will vary from 1 second for very small volumes
to several seconds for volumes of 1 litre and above. The time will also depend on the
size of the leak set in proportion to the test volume, small leaks on large volumes will
need longer times and large leaks on small volumes will need shorter times.
♦
Run the test several times, starting with the test item fully vented each time or with a
new test item each time if the item does not give consistent results, for example
moulded plastic parts. Adjust the Fill and stabilisation times as necessary and cure
any leaks to give a zero or acceptably small leak reading. Fit an identical leak tight
test item to the Reference port, if necessary, to reduce the overall cycle time.
Summary of Contents for FCO770
Page 2: ......
