Piston Position Detection Adjustment - Fluke PG9000 Series Operation And Maintenance Manual

5.2.2

Piston Position Detection Adjustment

 PURPOSE
To adjust the piston position measurement system.
 PRINCIPLE
The PG9000 piston position measurement operates on the LVDT (Linear Variable Differential
Transformer) principle. There is a pair of LVDT sensors embedded in the mounting post,
near the bottom, on opposite sides. The bottom of the mass loading bell has an iron speed
ring that couples with the field produced by the LVDTs. As the bell moves, the LVDT signal
changes proportionally to bell position, and therefore piston position. The signal is translated
into relative position in the ± 4.5 mm stroke of the piston (see Section 3.5). This provides a
non-contact method of determining piston position relative to a lower and upper travel stop.
The piston position and fall rate can be viewed from the [SYSTEM] run screen (see
Section 3.10.5.1).
The piston position indication system must be periodically realigned by a semi-automated on-
board routine. This routine defines and records the LVDT output at the piston HI and LO stop
positions.
 OPERATION
The operation of adjusting the piston position is different based on using a manual mass set
versus an AMH mass set. See the appropriate sections below based on which type of mass
set is being used.
•
Refer to piston stroke schematic Figure 14.
•
If the PG9000 Platform is equipped with an AMH mass set, see Special
Considerations When Using an AMH Mass Set.
Special Considerations When Using a Manual Mass Set
To adjust the PG9000 piston position indication system, load the mass bell on the piston and
a 5 kg mass disc. Then press [SPECIAL], <7cal>, <5Pposition>, <2cal>.
The prompt <Hold piston at max down stop> appears. Place the piston in the fully down
position – be sure the system pressure is vented and that the piston low stop springs are fully
compressed. Press [ENT]. The lower travel position is now defined.
The prompt <Hold piston at max up stop> appears. Increase pressure to the PG9000
TEST connection to raise the piston to the full top stop position.
The objective is to fully compress the springs so that the piston is truly at the high stop
position. Apply pressure underneath the piston that is the equivalent to at least 5 kg greater
than the pressure required to float the piston with the current load. For example, if a 10
kPa/kg piston-cylinder is being used, apply enough pressure that is at least equivalent to 5 kg
+ 5 kg = 100 kPag. Press [ENT]. The upper travel position is now defined.
Press [SPECIAL] and select <7cal>, <5Pposition>, <1view> to view the piston position
indication. Position is on the left and fall rate is on the right. The upper travel stop should be
+4.5 mm and the lower stop should be – 4.5 mm.
Special Considerations When Using an AMH Mass Set
The tubular binary masses of an AMH mass set have some influence on the piston position
detection system so it is important to adjust the piston position detection system with all the
binary masses loaded.
To adjust the PG9000 piston position system when an AMH mass set is being used, proceed
as follows:
 Vent pressure.
 Select [SPECIAL], <8AMH>, .<2control>, <2discreet> and load all of the binary masses
and none of the main masses (see Section 3.12.8.2). The binary mass values with an "*"
5. MAINTENANCE, ADJUSTMENTS AND CALIBRATION
Note
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