10-9
10
Pressurized Line Leak Detection
Pressure Offset
Pressure Offset
New transducers are now factory sealed and their internal chamber cannot be equalized to atmospheric pressure
by opening a vent screw as in the past. The Pressure Offset test procedure described in this section
must
be
performed when using new PLLD transducers with serial numbers of 100,000 or above, in sites located at
altitudes above 2,000 feet (609 m). Note: this procedure can also be used with transducers having serial numbers
below 100,000 instead of using the vent screw to equalize pressure.
Table 10-1 illustrates approximate absolute pressures that are for reference only. The transducer’s actual reading
may vary slightly due to its construction, A/D conversion, head pressure in the lines, etc.
Before this procedure is performed, the pressure in the line MUST be vented to zero. It is recommended that this
procedure be performed immediately after installing the transducer, before energizing the STP.
The first step is to vent the line(s). The second step is to go to the Diagnostic Mode and run a Pressure Offset Test
for each transducer to determine its Pressure Offset value. The third step is to return to the Setup Mode and enter
the Pressure Offset determined in the tests, for each transducer.
VENTING THE LINE
1. Turn Off, lock out, tag power to the STP.
2. Vent the line to zero.
3. Reseal the line.
4. Turn On power to the STP. Follow the procedure below.
Table 10-1. Reference of Absolute Pressure Offsets at Various Altitudes
Altitude
ft (m)
Atmospheric Pressure Offset
psi (kPa)
Sea level - 2000 (609)
No Change
2000 - 3000 (609 - 914)
+1 (+6.9)
3000 - 4000 (914 - 1219)
+1.5 (+10.3)
4000 - 5000 (1219 - 1524)
+2.0 (+13.8)
5000 - 6000 (1524 - 1829)
+2.5 (+17.2)
6000 - 7000 (1829 - 2134)
+3.0 (+20.7)
7000 - 8000 (2134 - 2438)
+3.4 (+23.4)
8000 - 9000 (2438 - 2743)
+3.8 (+26.2)
9000 - 10,000 (2743 - 3048)
+4.2 (+28.9)
10,000 - 12,000 (3048 - 3658)
+4.6 (+31.7)
12,000 - 14,000 (3658 - 4267)
+5.4 (+37.2)
14,000 (4267) - above
+5.7 (+39.3)
OFF
