Description The PR-276 incorporates sophisticated integrated circuits and a new micro-machined glass-on-silicon (Gl-Si) capacitance sensor to not only provide a high level, fully conditioned and temperature compensated output, but also to offer up to three (3) field selectable pressure ranges in one unit. The field selectable feature eliminates costly inefficiencies by providing a single unit which can be configured to cover all the pressure ranges for a particular application. For instance, 1.25", 2.50" and 5.00"wc are in one unit. To substantially reduce installation cost and to eliminate costly control panels, the PR-276 incorporates a pressure sensor and a static pressure tip integrated as one assembly. Two industry standard output versions are available, 4-20mA 2-wire loop or field selectable 0-5 VDC/0-10 VDC. Wide 12-40 VDC or 12-35 VAC unregulated supply voltage and a broad 25°F-150°F compensated temperature range ensures compatibility to most of the applications. Rugged NEMA 4 (IP-65) enclosure, gasketed cover, external mounting bracket, fully temperature compensated NIST traceable accuracy, and a liberal five year warranty are some of the features which make the PR-276 not only the most reliable, but the lowest installed cost duct pressure sensor in the industry. The PR-276 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-276 offers up to three field selectable pressure ranges in one unit. In this way, a customer does not need to know the exact pressure range prior to selection. A unit can be field configured for the desired pressure range in the field. With fixed range units, in case of engineering error or 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-276 with the field selectable pressure range feature eliminates above mentioned costly inefficiencies. A single unit can be configured to cover all the 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. To substantially reduce installation costs and to eliminate costly control panels, the PR-276 incorporates a pressure sensor and a static pressure tip integrated as one assembly. Instead of installing two devices, running a tubing from the static pressure probe to the pressure transducer and using up expensive space in the control panel, with the PR-276 one has to merely drill a 7/16" hole in the duct, insert the integral pressure tip, and use two sheet metal screws to complete the installation. The pressure tip has two precision orifices which are protected by baffles to significantly reduce any velocity pressure induced errors. The probe assembly is constructed out of extruded 6061T aluminum alloy. A gasket is provided on the bottom of the enclosure to seal against the duct. On 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 the 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, this protection circuit is designed in to ensure trouble-free start-up. The VDC output unit is also designed to handle low impedance circuits. In fact, the unit can drive up to 1K ohm minimum. In this way, multiple controllers, indicators, or other devices can be paralleled to the output without performance degradation. The 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 reverse polarity protection built in. As a result, it is next to impossible to damage the unit by mis-wiring. By using sophisticated low drop-out voltage regulators and CMOS integrated circuits, the mA output unit can drive very high output impedance. In fact, with only 12 VDC supply, the unit can drive 400 ohms. At 40 VDC, the unit is capable of handling up to a 3000 ohms load. In this way, the output loop can be tied in series to multiple controllers, indicators, and other devices without degrading the performance. Due to the low mass of the micro-machined capacitance Gl-Si sensor, the mounting orientation error is negligible. For extremely precise applications, 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. The PR-276 incorporates a rugged NEMA 4 (IP-65) fully gasketed, dust proof, and splash proof enclosure. The 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 is 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. The unit also has additional features for ease of installation including unpluggable terminal block, easily accessible zero and span trimmers, and conveniently located dip switches for field selection.