13 Flashcards
Temperature sensing device that changes its resistance to current flow based on its
temperature.
Thermistor
Device that uses two dissimilar metals that react differently to changes in temperature.
Outer tube has a high expansion rate and an internal rod of metal with a low expansion rate.
Rod and tube
Two unlike metal strips attached back-to-back, often brass and steel. The most
common device used to detect thermal change.
Bimetal
The changing volume of a liquid, when heated or cooled, is used to actuate a control.
Fluid expansion
Multiple devices wired in series with each other to provide a higher output voltage.
Thermopiles
This device uses a quick open-and-close feature in controls that stop and start electrical loads.
Snap disc
Temperature control used to maintain space or product temperature and to protect equipment from damaging itself.
Thermostat
Two unlike metals joined together at one end called the “hot joint”, that when heated on the fastened end, an electrical current flow is started.
Thermocouple
Thin flexible metal disc with a large area that will flex when pressure is applied
Pressure changes underneath the disc cause it to flex up or down.
Diaphragm
A split phase motor with a run capacitor only.
Permanent split capacitor
Accordion shaped device that has a lot of internal volume and a lot of travel.
Bellows
Explain how a thermocouple is used in a control system.
it sences the temp of the air intake of the room and shuts the unit off when it reaches the desired temp.
How are bimetal strips shaped/formed to increase range of movement?
They can be curved, shaped into a helix, or coil
A thermistor’s resistance increases when its temperature increases is known as -
PTC
What does the PTC thermistor do?
Regulates when current should be flowing
The output of a pressure transducer is typically a value of
Capacitance, inductance, resistance.
Controls can be classified as
Mechanical
Electrical
Electromechanical
Pneumatic
Digital
The faster a switch is opened, the longer it will last. T/F
T
Contact surfaces are bad if you see pitting or electrical arc burn marks. T/F
F
Brass and steel have a different rate of expansion and contraction when heated or cooled. T/F
T
Fluid expansion is a way to sense temperature change. T/F
T
Bellows are normally used with a vapor instead of a liquid inside it. T/F
T
A thermistor is a device that produces a voltage across the hot and cold junctions
when heated T/F
F
The resistance of a Negative Temperature Coefficient (NTC) thermistor decreases as its temperature decreases. T/F
F
Modulating controls are used to start or stop blower motors.T/F
F
Before removing pressure switches, ensure the removal will not cause an uncontrolled release of refrigerant from the system. T/F
T
A shorter bimetal will have greater travel. T/F
F
A loose electrical connection can cause an overload to function. T/F
T
Vapor is more sensitive to temperature change. T/F
F
The metal tube in the rod-and-tube control expands and contracts faster than the
steel rod. T/F
T
The control used to regulate temperature is called a
Thermostat
Bimetal controls are limited in application by what?
Warp
A thermal system overload may occur if a specific electrical or mechanical component is not cooled properly, resulting in
Overheating
A thermocouple is a device that
Converts heat to electrical energy
An example of a bimetal device is a
Snap disc
Fluid flow can be used to indicate temperature when used in this type of device. It operates the same as an analog gauge manifold to indicate pressure.
Burdon tube
