DH Instruments FPG8601, Руководство по эксплуатации и обслуживанию

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8. GENERAL MAINTENANCE
Page 121 © 2007 DH Instruments, a Fluke Company
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8.1 OVERVIEW
The topics in this section describe how to maintain the bubbling system and how to verify and correct the
zero of the vacuum reference sensor. The bubbling system is used to humidify the lubrication gas
surrounding the load cell. This prevents electro-static effects that can significantly effect system performance.
Whenever humidity cannot be obtained even after proper purging, check the bubbling system to make
sure there is still water in the system.
The vacuum reference sensor is a high accuracy low range device that is used by the FPG8601 to define
an absolute reference pressure, from the natural differential pressure determined from the load cell,
piston and cylinder (see Section 2.5). The most significant calibration aspect of this sensor is the change
in zero. Since the sensor only measures residual vacuum pressure typically less than 1 Pa (depending
on the vacuum pumps used), span error does not significantly impact the overall uncertainty of the FPG.
However, any zero offset in the sensor is directly transferred to the zero offset of the FPG. Therefore, it is
recommended that the zero of the sensor be checked prior to a series of calibrations in absolute mode.
An isolation valve is included with the FPG to minimize zero drift by avoiding the shock associated with
the change to atmosphere.
8.2 REFILLING THE BUBBLER ON THE FPG
When the bubbler’s water supply is diminished, the humidity of the lubrication pressure will decrease
causing instability in the system. This procedure states how to add water to the FPG bubbling system. In
this process, the FPG lubricating volume is vented. This will ensure that all gas has been removed from
the lubricating volume and the surrounding areas. Once the process is complete, the system will be
returned to normal calibrating conditions.
Table 43. Bubbler Maintenance Equipment
EQUIPMENT
FPG
FPG Tools Software
Distilled Water
Remove the pressure from the FPG by pressing the
[Shut Down]
icon on FPG Tools when the FPG
is in gauge mode (see Section 5.9).
It is critical to never tilt the FPG when there is pressure in the system. If this occurs, water from the
bubbler will be forced through the lubrication gas lines and into the lubricating volume. This can cause
permanent damage to essential parts of the FPG.
Wait for FPG Tools to display “The FPG is shut down” on the
<Status Bar>
.