While the 24-volt electrical control system could only energize a damper fully open or fully closed, a pneumatic control system can hold that damper at 25%, 40% or 80% open. The pneumatic system is very durable, is safe in hazardous areas where electrical sparks must be avoided, and most importantly, is capable of modulation, or operation at part load condition. The copper or plastic tubing carry the control signals around the building, which is relatively inexpensive. By varying the discharge air pressure from these devices, the signal can be used directly to open valves, close dampers, and energize other equipment. Pneumatic actuators are described in terms of their spring range.Ĭompressed air with an input pressure can be regulated by thermostats and humidistat. The most popular control system for large buildings historically has been pneumatics which can provide both On-Off and modulating control. Liquid Level Measurements which include:.Quartz Crystal Relative Humidity Sensor.Relative Humidity Sensors which include:.The typical current range is 4 to 20 mA (milliamps). Current sensors could be used for temperature, humidity, and pressure.Typical voltage input ranges are 0 to 5 Vdc (Volts direct current), 1 to 11 Vdc, and 0 to 10 Vdc. Voltage sensors could be used for temperature, humidity and pressure.Examples are BALCO elements, Copper, Platinum, 10K Thermistors, and 30K Thermistors.
Resistance sensors are ‘Resistance Temperature Devices (RTD’s)’and are used in measuring temperature.
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