Differential Pressure Indicator, Low and High Limit Control, 4-20 mA Transmitter

the 3000SGT Series Photohelic● / Switch / Differential Pressure Gauge / Transmitter combines several key control functions in one unit and is easy to install. This multifunction instrument uses the industry-recognized standard Dwyer Magnehelic differential pressure gauge to reliably measure low-pressure air. It can measure positive, negative, or differential pressure within ±2% accuracy. This time-tested differential pressure gauge reliably displays the pressure of air or compatible gases on a 4-inch diameter, 80° scale dial. The gauge operates completely independently — it can even work normally during a power outage. In addition, adding two low/high limit controls (or pressure switches) with double-pole double-throw relays can directly drive 10 Amps @ 28VDC or 120/240 VAC. Each setpoint has a deadband of one pointer width — less than 1% of full scale — just enough to ensure a definite position and prevent oscillation. Internal holding coils allow users to connect and separately control the deadband for both changes, making it ideal for positive pressure systems in cleanrooms and buildings, heating, ventilation and air conditioning systems, automatic air filters, air calibration, and many other applications. Setpoints can be freely adjusted across the full pressure range using the red pointer and front knob. Finally, the Photohelic switch/differential pressure gauge/transmitter includes a separate 4-20 mA, 2-wire transmitter that operates on 10-35 VDC and has separate zero and span adjustments at the rear. For 100-240V AC input to 24-28V DC output, it’s best to use the A-700 power converter, and the transmitter works well for driving variable-speed fans and blowers, valve positions, and is also suitable for computer VAV systems or continuous data acquisition on strip chart recorders. Besides combining all these control functions in one unit to significantly reduce cost and space, it also uses a single set of pneumatic connections to replace three or four, saving both time and materials.