3. OPERATION
Page 67
© 1995 - 2010 Fluke Corporation, DH Instruments Division
3.4.4.4.2
Run AutoZ
Run AutoZ is the function by which the current RPT reading is compared to a
reference,
P
std,0
, at atmospheric pressure to determine a new value of
P
offset
.
The value of
P
offset
is then used by AutoZ to automatically correct the RPT for
possible change in zero over time (see Section 3.4.4.4, PRINCIPLE).
There are 3 program limits on the entry of
P
std,0
in place to reduce the possibility
of erroneous entries from either method, limits given in kPa absolute but directly
convertible to the current unit of measure:
1) The entry must be within the limits of 70-110kPa absolute;
2) If the entry is => 0.01% of nominal full scale from the current reading of either
RPT, the will warn that the value is high for the specific
transducer(s) but accept the entry;
3) If the entry is => 0.02% of nominal full scale from the current reading of either
RPT, the will warn that the value is too high for the specific
transducer(s) and reject the entry;
In the case of 3), the pressure calibration of the RPT’s or the accuracy or
calibration of the pressure reference used to obtain
P
std,0
should be double-checked.
While an entry within the limits of 1) or 2) is acceptable, if running AutoZ results
in a value of Poffset that is greater than ± 0.005 % FS of the span of the RPT that
is being AutoZeroed, the RPT and/or the reference used as the source of Pstd,0
may be out of tolerance or the AutoZ process may have been faulty. Before
activating a new Poffset greater than ± 0.005 % FS of the active RPT, check to
be sure that both the RPT and the reference were in good working order,
properly vented to stable atmospheric pressure, at the same height, and reading
in the same pressure units when AutoZ was run. A good laboratory practice
would be to keep a log of the resulting AutoZ
P
offset
values for the two
transducers over time to look for trends.
To access run AutoZ, press
[TARE]
,
<4AutoZ>
,
<4run>
. The display is:
1.
Selection of source of
P
std,0
reference from
which to AutoZ.
AutoZ by:
1Entry 2COM2
Selecting
<1Entry>
allows the value of
P
std,0
to be entered from the front panel keypad.
Selecting
<2COM>
allows the value of
P
std,0
to be read automatically from a
DHI
RPMx connected to ’s COM2 communications port.
When AutoZ is run, the internal valves are actuated to connect both
RPTs to the channel A, Hi port on the rear panel (see Figure
14 in Section 5.2.4.1). Be sure the channel A, Hi port is fully open to atmosphere
when running AutoZ. Note that the quick connectors and to
molbloc pressure lines are self sealing and therefore DO NOT open to
atmosphere unless a quick connector stem is inserted. Use a quick connector stem
(
DHI
P/N 3068652, equivalent to Swagelok SS-QM2-S-200) supplied with the
accessories to open the port to atmosphere.
Note
•
Allow the to stabilize at atmospheric pressure
and ambient temperature for 10 to 15 minutes before
running AutoZ.
