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What is the difference between a transmitter, intelligent sensor and sensor controller?

Sentera offers three sensor types: transmitters, intelligent sensors, and sensor controllers. The main difference between these types is the functionality, or the behaviour, of the output.
Sentera offers devices to measure, regulate or control the following parameters: temperature, relative humidity, CO2, air quality or VOC, toxic gases (CO, NO2, LPG), ambient light, differential pressure, air volume flow or air velocity. Most sensors measure at least two parameters simultaneously. 
A transmitter or sensor is a device that measures a certain parameter. The device translates the measured value(s) into analogue output(s) or Modbus RTU register(s). You can use these sensors to only measure and not control, in which case they are not suitable for demand-based ventilation. However, it can still be interesting to know how much of a certain parameter is present in a room or to have a sensor with an alarm module. You could also use some of these sensors for demand-based ventilation. In that case, you must select one output to control your fan. 
E.g. a temperature and relative humidity sensor will transfer both measured values into two separate 0-10 Volt output signals. Either both values are readout values, the temperature sensor controls the fan (speed controller), or the relative humidity sensor controls the fan (speed controller):

 T and rH graph for Sentera Sensor


An intelligent sensor can define a range for each of the values that it can measure and control. Intelligent sensors have only one output. This output is regulated to keep all measured values within their predefined ranges. The sensor can switch its output control between values “intelligently” when one of them threatens to go out of bounds. 

When all measured values are at their minimum range, the sensor output will remain at its minimum value. When one of the measured values starts to rise towards its maximum range, the sensor output will also increase towards its maximum value. Intelligent sensors are typically used for demand-based ventilation or demand-based fan speed control. They are used in circumstances where multiple parameters in an environment must be controlled. For example, in a restaurant kitchen, both relative humidity and temperature control are important. 

E.g.: an intelligent sensor that measures temperature and relative humidity regulates its output to keep both temperature and relative humidity within their pre-defined ranges. The output (AO1) changes automatically depending on the highest of the temperature or relative humidity values. This automatic change ensures that the highest of the two output values controls the output. In the diagram below, the green line is the output control value. 

 T and rH diagram

A sensor controller offers the possibility to define a setpoint for a single parameter. This setpoint is the greatest difference between this sensor type and the others. Instead of a range of values, only one point is acceptable for the sensor. 

This category contains only the Sentera sensors that measure differential pressure, volume flow and air velocity. It is a separate category because it does not have a proportional output, but a PI algorithm. PI stands for Proportional Integral. It is a control loop that continually calculates a correction between a setpoint and the actual measurement. 

The PI algorithm controls the analogue output. The PI algorithm ensures that the controlled parameter retains its setpoint value. 
E.g.: the differential pressure controller controls the 0-10 Volt output to maintain the differential pressure at the requested setpoint.

Differential pressure perational dagram

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