A sensor is simply a device that has to perform the duty of detecting or discerning the change or variation in its surrounding or any parameter assigned to it and is further sent either to a display or to a controller. The key features that a sensor needs to have are unerring accuracy & precision, high resolution, high sensitivity, good response time, reproducibility etc.
Sensors are devices that can be found in most of the appliances you see around. From an iron box, electric geyser, air conditioner to bikes and cars. The objective or its purpose in each item may be different, but its plays a vital role in each of them.
Commercial buildings have larger floor areas & occupancy and hence distribution of LED lights is widespread in these areas. Given the flexibility of today’s work culture, these are never fully occupied and always have some area where there is zero occupancy with no illumination required. It is humanly not possible to keep a tab over this & manually control them. Here come the ceiling mounted motion sensors that use infrared signals to detect heat and movement thereby illuminating only the occupied area & help save power
With speed limits come in place while driving on highways, you simply look at the speedometer to keep a tab on it and avoid being fined. But ever wondered how these speedometers work? Yes, sensors again. Magnetic sensors to be precise whose signals/outputs are further amplified & that help display not just the speed but also the total distance traveled which is a function of the odometer
Talking about pharmaceutical factories, hospitals, hotels etc., the critical parameters to be controlled here are mainly temperature, pressure & RH (Relative humidity). In any plant, the most power sucking systems are always the HVAC systems and hence, it is extremely crucial to monitor and control these when the desired condition is achieved & avoid consuming excess power. Listed below are the types of sensors and the ones that we use in our installations.
Sensors basically segregate into 2 types:
- Passive Sensors
- Active Sensors
1.Passive Sensors :- Passive Sensors detect and respond to inputs from the physical environment. These do not require an external power source and gather data through the detection of vibrations, light, radiation, heat or other phenomena related to the subject’s environment. For example, Thermocouple, Resistance temp detectors, Antennas etc.
2. Active Sensors :- Active Sensors require an external power source so as to control current or voltage & thereby perform the desired task. These sensors might transmit energy or drive a signal. For example, the active sensor (0-10 V) used for measuring temperature in ducts.
- Active Temperature Sensors:
In HVAC projects, these are mounted in the return air duct to monitor the temperature of the area.
Recommended where only temperature is to be maintained (CNC areas) and control over RH is not required.
They sense as per the set point and accordingly give an analog output i.e. 4-20mA or 0-10 VDC.
The controller received this input and will switch on/off the DX (Direct Expansion) unit or modulate the supply of chilled water in case of a CHW system.
- Active RH Sensors:
These too are mounted in the return air duct to monitor the humidity of the area.
They sense as per the set point and accordingly gives analog output i.e. 4-20mA or 0-10 VDC,
- Temp + RH Combo sensor:
These are the most commonly used sensors because of its 2 in 1 configuration.
Recommended for all classified areas where temperature & RH both are to be controlled.
They sense as per the set point and in turn give 2 analog outputs; One to control the temperature by switching on/off the DX unit or modulating the supply of chilled water & the other to control the RH by switching on/off the heater or modulating the supply of hot water.
- Multi Point Velocity Sensor:
Mounted in the supply air duct to measure the velocity of air discharged by the AHU.
Recommended where the AHU’s plug type blowers run in tandem with a Variable frequency drive (VFD) that delivers only the required frequency to the blower motor thereby leading to high savings in power.
It has multiple sensing points that monitor the air velocity and provides an analog output on any variation from the set point. (Air velocity drops when filters aren’t cleaned regularly and start choking)
The VFD receives this signal and will ramp up/down the blower’s motor frequency accordingly.
- Differential Pressure Transmitter (DPT):
Mounted in the supply air duct to measure the differential pressure of air discharged by the AHU.
Recommended where the AHU’s plug type blowers run in tandem with a Variable frequency drive (VFD) that delivers only the required frequency to the blower motor thereby leading to high savings in power.
Operation is very similar to Velocity sensors except that these measure the drop in pressure or variation from the set point when the filters start choking.
Above mentioned sensors are the ones regularly used in HVAC projects for monitoring and controlling the key parameters i.e. temperature, pressure & RH. As the need to monitor increases & with many opting for EMS/BMS, more and more sensors get added which are similar to these but are compatible to EMS/BMS systems.
Sensors play a very important role in not just monitoring and controling the various parameters in the appliances we see around us but these highly efficient detectors also help in drastically reducing the consumption of electricity and save power which in today’s world is the most sought out feature in any item. For any query or clarification, do write to us at fernando.n@hvax.in .