4. OPERATION
Page 59
© 2005 - 2007 DH Instruments, a Fluke Company
In normal operation, the
ADCS Tools
software that manages the ADCS-601-AF system,
determines which pressure standard system to use based on the pressure value to be set.
ADCS Tools
also handles the transition from one standard to the other when the requested
pressure point requires changing the active pressure standard.
There is always an active pressure standard (see Table 11). Active is defined as connected
to the ADCS-601-AF
TEST(+)
port. Changing the active pressure standard requires
changing the states of the PG and FPG ISOLATION valves (valves 1 and 2) (see Figure 29)
without causing excessive perturbation to the pressure applied to the
TEST(+)
port and the
device under test. This is accomplished by using the two PPC3 pressure controllers to set
the same pressure on either side of the isolation valve. Once this transition pressure has
been set and stabilized, the valves are operated. The default transition pressure is 15 kPa in
absolute mode and 14 kPa in gauge mode. The value can be changed in
ADCS Tools
,
[Setup]
,
[Configuration]
,
[Limits]
but this is not recommended.
The transition between standards is initiated automatically when a pressure request is made
that requires the standard that is not currently active. A transition can also be initiated using
the
[Standard Transition]
button on the
ADCS Run Screen Toolbar
(see Section 4.3.5.3).
Table 11
.
Valve states
Valve states
(1 = open, 0 = closed)
Meas.
mode
Active
standard
1
2
4
6
9
10
11
Reference
vacuum
pumps
PG7601 1 0 0 0 1 1 1
on
absolute
FPG8601 0 1 0 0 1 0 1
on
PG7601 1 0 1 1 1 1 1
off
gauge
FPG8601 0 1 1 1 1 0 1
off
Note: For valve references, see Figure 29, ADCS-601-AF simplified operational schematic.
Figure 29
.
ADCS-601-AF simplified operational schematic
4.1.4
DIFFERENCE BETWEEN REQUESTED AND ACTUAL SET
PRESSURE
ADCS-601-AF is not designed to set exactly the pressure that has been requested. Rather, it
sets a value of pressure very close to the requested pressure and returns the exact pressure
value it has set.
The majority of the ADCS-601-AF pressure range (15 kPa (4.5 inHg) and up) is covered by
an automated PG7601 piston gauge (see Section 2.2.1). The automated mass handling
system of the PG7601 can load mass in steps of 0.1 kg. On the PG7601’s 10 kPa/kg piston-
