Which of the sensors does not require external power supply?

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Which of the following device is self powered control device?
What is the smallest leak that an electronic leak detector is cable of sensing per year?
In which of the following heat pump cycle, the auxiliary heating element will be operated?
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What is the maximum allowed relative humidity to maintain indoor air quality as per ASHRAE?
Where does the defrost thermostat is located in heat pump?
If there is a voltage reading in voltmeter which is connected across thermostat terminals indicates ……………………
Which of the following is not a heat pump class?
In heat pump, what is the function of indoor coil in cooling cycle?
The amount of water vapor that moisture contains increases rapidly with increase in temperature.
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The defrost thermostat closes when the temperature of outdoor coil drops to …………….
Which of the following are benefits of HVAC control system?
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A bourdon tube sensor is used to measure ………..
Which of the following heating mechanism will have high efficiency?