7. MAINTENANCE OF TRACEABILITY AND RECALIBRATION
Page 143
© 2005 - 2007 DH Instruments, a Fluke Company
Calculate the mass load value corresponding to one count by dividing the
number of counts (
<N>
) by the total true mass loaded since the balance was
zeroed. To obtain the total true mass value, add up the true value of all the
masses loaded (except the first 500 g that was tared out). The true values of
the individual masses can be found in the mass set Calibration Report.
For
example:
Total true mass load: 1501.756 g
Counts (
<N>
) indicated with total true mass load: 1 488 663
Value of 1 count: 1 488 663 / 1501.756 g = 991.2815 count/g
Predict the balance output at other mass loads by multiplying the value of 1
count calculated in by the true mass load.
For
example:
Total true mass load 500.664 g
Predicted output (
<N>
): 550.664 g * 991.2815 count/g = 545 863 count
Find the difference between the predicted output and the actual output
logged when the mass was loaded:
Predicted output (
<N>
): 545 863 count
Actual output (
<N>
): 545 862 count
Difference: 1 count
Compare the difference between the predicted output and the actual output
to the linearity tolerance to determine an pass or fail condition.
Difference between the predicted and actual outputs: 1 count
Linearity tolerance: +/- (2 (2 ppm * 454 863)) = +/- 3 counts
Pass fail condition: Pass
If the any load cell linearity verification point results in an fail condition, repeat the
verification process, including the initial zeroing of the load cell with the CLB and
500 g mass loaded. Be sure the load cell output is stable at each point.
If the load cell linearity verification consistently has one or more fail conditions,
the FPG8601 requires factory service. Contact DHI or an DHI Authorized
Service Provider (see Table 26).
7.2.6
FPG8601 AND PG7601, ZERO REFERENCE VACUUM CDGS
The FPG8601 and PG7601 use independent capacitance diaphragm gauges (CDGs) to
measure the reference vacuum pressure in absolute measurement mode.
The CDGs are known to often have significant zero drift that is easily corrected by zeroing
their output at a very low vacuum.
The CDGs cannot be zeroed properly in the normal operating position but the ADCS-601-AF
includes facilities to easily zero the CDGs on the system. This avoids requiring separate vacuum
facilities and offers the convenience of not needing to disconnect the CDGs electrically.
To zero the ADCS-601-AF CDGs proceed as follows:
Prepare the ADCS-601-AF:
Put the ADCS-601-AF system into gauge mode and wait for the mode change to
complete (see Section 4.2.3).
Vent the ADCS-601-AF system by pressing the
[VENT]
button on the
ADCS Run
Screen
. Wait for the operation to complete.
