mensor PCS 400, Operation Manual

Page: 83 / 118

8a – Gauge Transducers (Absolute Emu-
lation) without BRT
A
PCS 400
equipped with from one to three internal
gauge pressure transducers (no Barometric Refer-
ence Transducer) with the absolute pressure emu-
lation option is configured as shown in the
pneumatic schematic of figure 9.3 in the
Appendix .
A requirement for absolute emulation with this
configuration is a vacuum source of at least 21
liters per minute capacity on the REFERENCE
port. Each transducer that will function in the
emulation mode will require separate zero and
span calibrations for each mode to achieve the
greatest possible accuracy. To control pressures at
or below atmospheric pressure a second vacuum
pump is required on the EXHAUST port (see Op-
tion 7). Mensor supplies both gauge and absolute
calibration data for each transducer with this op-
tion. These calibrations should be maintained
separately throughout the life of the instrument.
8b – Gauge Transducers (Absolute and
Vacuum Emulation) with BRT
This system configuration is shown in figure 9.4 in
the
Appendix. All internal transducers (except the
Barometric Reference Transducer) must be gauge
units. With the internal BRT the REFERENCE port
vacuum pump is not required. Each tranducer that
will be used to control negative (vacuum) pressures
must be bi-directional to –15 psig (see Option 7).
The effect on a transducer when toggled between
gauge and absolute modes depends on the
transducer’s native mode and which direction it is
switching to as shown in table 8.1.
NOTE:
Techniques and equipment are
currently not available for calibrating ex-
tremely low range absolute transducers.
Instruments using such sensors may not
achieve the rated accuracy when control-
ling absolute pressure near a perfect vac-
uum. Use only transducers above 7 psi in
the absolute emulation mode for best
results. Refer to the ‘Limits’ function in
the Local Operation section to see how to
select specific transducers.
Table 8.1 - Effects of mode switching (Gauge Transducer)
Transducer Native Type Effect when Gauge mode
is switched to absolute
Effect when Absolute mode
is switched to gauge
Gauge
1. The current control point is aug-
mented by 14.696 psi. 1. The current control point is aug-
mented by 14.696 psi.
2. The control limits are increased
by 14.696 psi. 2. The control limits are decreased
by 14.696 psi.
3. All subsequent pressure read-
ings are the sum of the active
transducer reading and the current
barometric pressure.
3. All subsequent pressure read-
i n g s a r e t h o s e o f t h e a c t i ve
transducer
Table 8.2 - Effects of mode switching (Absolute Transducer)
Transducer Native Type Effect when Absolute mode
is switched to gauge
Effect when Gauge mode
is switched to absolute
Absolute
1. The current control point is increased
by 14.696 psi. 1 . T h e c u r r e n t c o n t r o l p o i n t i s
decreased by 14.696 psi.
2. The control limits are increased by
14.696 psi. 2. The control limits are reduced by
14.696 psi.
3. All subsequent pressure readings
are calculated by subtracting the
current barometric pressure from the
active transducer reading. 3. All subsequent pressure readings
are those of the active transducer.
OPTIONS
PCS 400
8-10 www.mensor.com