Thermocouples & Thermopiles
How does a standard thermocouple generate an electrical potential?
By converting thermal energy directly into electrical energy at a junction of two dissimilar metals
What is the defining characteristic of a Negative Temperature Coefficient (NTC) thermistor?
Internal resistance decreases as temperature increases
On an oscilloscope display, how many times does a standard residential single-phase AC sine wave hit zero efficiency per cycle?
Twice
What is the primary purpose of a Variable Frequency Drive (VFD) in an HVAC application?
to precisely control AC motor speed to match system load and save energy
According to commercial facility metrics, what combined percentage of a standard building's total energy budget is consumed by space cooling, heating, and ventilation?
34%
What is the expected Direct Current (DC) voltage output of a healthy standalone residential thermocouple operating under a load?
30 millivolts
What is the defining characteristic of a Positive Temperature Coefficient (PTC) thermistor?
Internal resistance increases as temperature increases
What is the angular displacement between the three overlapping voltage waves in a commercial three-phase electrical system?
120 degrees out of phase
Which electrical components are used in the DC Bus section of a VFD to smooth out voltage ripples?
Capacitors
Fan airflow pressures are usually measured in which units?
Inches of water column (WC)
How are individual thermocouples wired together inside a thermopile?
Series configuration
How does an electronic inductive pressure transducer identify pressure changes?
By shifting a magnetic iron core within an electromagnetic field to change inductance
What is the primary practical advantage of three-phase power over single-phase power for commercial motor operations?
The net flow of delivered power never drops to zero, ensuring smooth efficiency
What specific component type does the Inverter stage of a VFD utilize to rapidly switch DC voltage?
Insulated-Gate Bipolar Transistors (IGBTs)
What is the generally accepted range for evaporator air flow in CFMs per ton of residential air conditioning?
350 to 450
What is the standard voltage output range produced by a functional industrial thermopile?
750 millivolts
How does a potentiometric pressure transducer modify circuit metrics?
It moves a mechanical wiper arm across a resistive track to change resistance
How can a technician instantly reverse the operational spinning direction of a three-phase AC motor?
By swapping any two of the three incoming hot power wires
What electrical modulation technique do VFDs use in the inverter stage to reconstruct an artificial AC sine wave?
Pulse Width Modulation (PWM)
The temperature rise method formula for determining air flow is written as:
CFM = BTU ÷ (1.08 x Delta-T)
What type of gauge is used to measure a deep vacuum of 500 microns?
An electronic vacuum gauge
A compound pressure gauge measures which two metrics
Pressure and vacuum
What is the function of the Rectifier stage within a standard Variable Frequency Drive?
It uses a network of diodes to convert incoming AC power into rough DC voltage
How does a VFD directly regulate the physical speed of an attached AC motor?
By adjusting the applied line frequency (Hz) up or down
10 lbs. of refrigerant passes through a water-cooled condenser, losing 20 BTUs of heat per lb. If 10 lbs. of water passes through entering at 80°F, what is the leaving water temperature?
100 degrees F.