8. GENERAL MAINTENANCE
Page 127
© 2007 DH Instruments, a Fluke Company
Table 46.
Effective Area Calculation Variables
VARIABLE
DEFINITION
ρ
air
Calculated density of air.
ρ
N
Nominal density of Air at 0°C, 101.325 kPa and 0 %RH.
The value is = 1.2928 kg/m
3
.
P
Measured ambient pressure in Pa.
PN
Nominal ambient pressure = 101325 Pa.
T
Measured ambient temperature in K.
TN
Nominal ambient temperature = 273.15°K.
Z
Compressibility of air at the current ambient pressure
and temperature. This value can be obtained from the
NIST web site.
ZN
Nominal compressibility of air = 0.99941.
H
Measured percentage of relative humidity.
ρ
mass
Density of calibration mass.
M
Indicated mass of the calibration mass. This value is
read directly from the scale.
mT
Calculated true mass of the internal calibration mass.
8.4.5
PUT THE MASS BACK INTO THE DRIVE ASSEMBLY
Lift the drive assembly high enough from the standoffs to slide the mass into the assembly.
Gently place the mass and drive assembly back onto the standoff. Make sure that the
cables going from the drive assembly to the motor and pass through do not obstruct any
functions of the mass or load cell. If the cables make contact with the mass, the internal
calibration of the load cell will fail or yield faulty results.
Attach the drive assembly with the four M4 SHC screws and split washers.
8.4.6
REATTACH THE LOAD CELL COVER
Remove the cap from the load cell cover.
Form the large o-ring into the O-ring groove of the load cell plate. Note that sometimes
the o-ring will come out of the groove. Be careful not to tighten the load cell cover until
you are certain that all of the O-ring is within the groove.
Hold the load cell cover on its sides so that the bubble level is towards you. Gently slide
the back right internal wall of the load cell cover on the external wall of the heat sink.
Once the load cell cover is almost down, ensure that the post extending upward from the
load cell is aligned with the load cell cap.
Secure the load cell cover using the six M6 SHC screws.
8.4.7
FINAL STEPS
Turn on the FPG terminal. The calibration drive assembly will automatically raise the mass.
FPG Tools will re-establish communications with the FPG within 30s after the power is
turned on. If this does not happen, make sure that the RS232 cable is properly
connected to the FPG and PC. If communications still does not re-establish, remove the
load cell cover and make sure that the internal calibration mass is properly mounted and
that there are no cables interfering with the load cell or internal calibration mass assembly.
In FPG Tools select the
[Config]
,
[FPG Calibration Setup]
menu choice. On the
<FPG
Calibration Setup>
form, enter the new true mass value in the
<Calibration Mass>
field.
Click the
[Save]
button to activate the change.
Run a new internal calibration prior to running any calibrations with the FPG.
