PR-274/275 incorporates a new micro-machined glass-on-silicon
(Gl-Si) capacitance sensor. This technology revolutionizes
very low pressure measurement. Temperature related zero
drift, calibration shift due to overpressure, non-repeatability,
non-linearity, and extremely low pressure sensitivity have
been some of the problems which have plagued the controls
industry. The PR-274/275 with the new Gl-Si technology
not only addresses all of the above shortcomings, but for
the first time offers a reliable, accurate means to measure
and control building/room pressure, air flow, duct pressure,
filter pressure drop, or any other extremely low pressure
application. Up to six field selectable direct or compound
enclosure types, field selectable outputs, fully temperature
compensated NIST traceable accuracy, non-interacting zero
adjustments, short circuit and reverse polarity protected
output, and a liberal five year warranty are some of the
features which make the PR-274/275 the industry's highest performance,
ultra-stable, low pressure sensor.
PR-274/275 incorporates sophisticated integrated circuits
to not only provide a high level, fully-conditioned, and
temperature compensated output, but also to offer field
selectable flexibility which was unheard of in the industry.
The PR-274/275 offers up to six field selectable pressure
ranges in one unit. In this way, a customer does not need
to know the exact pressure range prior to selection. By
merely knowing the application, a unit may be selected
and then later field configured for the desired pressure
range. With fixed range units, in case of engineering error
incorrect selection, the only solution is expensive
field recalibration or time consuming product exchange
or replacement. Similarly, numerous units have to be kept
in stock as spares to cover all ranges in case of field
failure. The PR-274/275 with the field selectable pressure
range feature eliminates above mentioned costly inefficiencies. A single unit can be configured to cover all pressure ranges in a particular application thereby eliminating
any possibility of incorrect range selection. Additionally, one unit can be kept in stock and, in the event of a failure, it can be field configured thereby eliminating the need to stock numerous fixed range units. (For a complete listing of all ranges available, please see the ordering information section on page three.)
VDC output units, two additional field selectable options
are available: dual outputs 0-5 or 0-10 VDC, and
dual unregulated supply voltages 12-35 VAC or 12-40 VDC. By
merely setting a dip switch, one can select the desired output for
the specific application. As far as supply voltage is concerned,
the unit automatically configures for AC or DC and no field
selection is necessary. Another feature is that the output
is fully protected from short circuit to ground, or if
the supply voltage is applied by mistake to the output.
Past experience demonstrates that field related wiring
problems do occur. Instead of denying this fact, the protection
circuit is designed in to ensure trouble-free start-up.
output unit is also designed to handle low impedance
circuits. In fact, the unit can drive up to 1k ohms minimum.
In this way, multiple controllers, indicators, or other
devices can be paralleled to the output without performance
mA output units can function over a wide unregulated supply
voltage range: 12-40 VDC without any effect on calibration
or performance. The unit has built-in reverse polarity protection. As a result, it is next to impossible to damage
the unit by miswiring. By using sophisticated low drop-out
voltage regulators and CMOS integrated circuits, the mA
unit can drive very high output impedance. In fact,
with only 12 VDC supply, the unit can drive 200 ohms. At
40 VDC, the unit is capable of handling up to a 1600 ohm
load. In this way, the output loop can be tied in series
to multiple controllers, indicators, and other devices
without degrading the performance.
to low mass of the micro-machined capacitance Gl-Si sensor,
the mounting orientation error
for ranges higher than 1.0"wc (250 pa) is negligible.
For extremely low ranges, if the unit is installed as indicated
on the label, there should be no orientation error. However,
due to space limitation, if the unit cannot be installed
in the indicated position, the error can be easily removed
by merely adjusting the zero trimmer.
Since the zero and span trimmers are non-interactive, adjustment
to the zero should under no circumstance affect the calibration
integrity of the unit including linearity and repeatability
specifications across the range.
PR-274/275 is available with two packaging options: a NEMA 4
(IP-65) fully gasketed, dust proof and splash proof enclosure,
or a lightweight but rugged panel mount chassis for ease
of installation with minimum space requirement in a control
panel. The NEMA 4
(IP-65) enclosure has an external mounting bracket to facilitate
field installation. A ½" (.875"/22.25
mm diameter) knock-out for conduit connection is also provided.
A liquid tight cable connector is also supplied if the unit
not being hard wired. Once installed, the enclosure maintains
its environmental rating and protects the electronics and
the sensing element from condensation, corrosive contaminants
and other environmental pollutants. Both packaging options
also have additional features for ease of installation, including
unpluggable terminal blocks, rugged brass hose barbs, easily
accessible zero and span trimmers, and conveniently located dip switches for field selection.