Micromeritics FlowSorb III 2305 Operator's Manual page 52

Performing a Multipoint Surface Area Measurement
4. Use the Coarse and Fine Zero knobs to zero the instrument. Observe the
display for a few minutes to establish system stability. A change of no more
than 0.01 should be achieved.
The two primary factors leading to excessive instability are:
•
instrument warm-up, which may require up to 30 minutes after initial
power application, and
•
the progression of residue from a previous analysis, which can require as
much as 10 minutes for elimination.
Be sure these situations do not exist when setting the zero. Once set, the
zero should not be readjusted unless a sustained change beyond ± 0.02 units
occurs.
5. Depress the Surface Area and the Clear SA Display pushbuttons.
6. Hold the syringe at the rear flange so that body heat does not affect the gas
volume contained by the syringe barrel.
7. Insert the needle fully into the Inject septum.
8. Inject the gas at a moderate rate. Withdraw the needle when the syringe is
completely discharged.
•
After approximately one minute (five minutes for Long path), the Thresh-
old light begins to flash and the indicator starts to accumulate surface area
information.
•
When the Threshold light ceases to flash for 15 to 20 seconds
(approximately after three minutes), the accumulation may be considered
complete.
•
Completeness may be confirmed by pressing the Det pushbutton; it should
be 0.02 or less.
9. Use the Calibrate knob to set the gas volume at standard conditions (refer
to Appendix A). For example, if ambient temperature is 22 °C and atmos-
pheric pressure is 740 mmHg, set the gas volume as
as calculated by equation 8, Appendix A.
Hereafter the instrument will indicate the adsorbed gas volume (STP) instead
of the equivalent surface area of an adsorbent as in the single-point proce-
dure.
3-12
1.00 x (273.2/295.2) x (740/760) = 0.90
FlowSorb III
0.90
Mar 2012