DH Instruments GFS2102, Руководство по эксплуатации и обслуживанию, Страница: 22 / 206

GFS2102™ OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company Page 6
In order to mitigate mass measurement errors due to balance drift over time, the balance sits inside an
automated mass handling platform assembly, AMH-GFS2102, that allows the cylinder assembly to be lifted off
the balance, and a reference mass to be loaded on the balance, without interrupting the flow measurement.
The Laboratory Conditions Monitor (LCM) is a central piece of hardware for GFS system operation. It performs
several different functions for the system. These include measurement of temperature under the AMH platform,
measuring temperature and humidity surrounding the reference gas cylinder, measuring the temperature of the
reference gas cylinder, actuating the AMH platform movement, measuring ambient pressure and recording the
precise time at which each balance reading is taken. Another piece of support hardware, MFC-CB is used for
sending flow command signals to the flow controllers, and possibly reading the device under test if the device
has a voltage output.
2.1 BALANCE AND AMH-GFS2102
GFS2102 measures the changing reference gas cylinder mass using a high precision 2.3 kg range mass
balance. It is a mass comparator type balance, so there is no significant deflection of the mass tray while
the mass load is placed on it. The balance has a digital serial output which is read by the LCM.
In a typical mass measurement, the balance can be zeroed, or tared, immediately before placement of the
mass, and the measurement can be made relatively quickly after zeroing. Since gravimetric gas flow
measurements can require up to several hours or days for some gases and flow ranges, the balance’s
stability over time and level of influence from surrounding conditions becomes very significant to GFS2101
measurements.
A key to reaching the desired level of uncertainty using GFS2101 is to eliminate or minimize the uncertainty
due to drift of the mass balance over time. In order to quantify and correct for the balance drift, a specialized
automated mass handling platform called AMH-GFS2102 has been developed to allow the GFS balance to
be AutoZeroed at selected intervals during a flow measurement. The AMH alternately lifts the reference gas
cylinder assembly off the balance, loads a fixed reference mass in its place for measurement, and returns the
reference gas cylinder assembly without interrupting the flow measurement.
Figure 2. Reference gas cylinder resting on GFS balance and AMH-GFS2102