EC (Temperature Control) Ch 9 Flashcards
(12 cards)
What are the three basic types of temperature sensing devices?
- Thermocouples
- Resistance Temperature Detectors (RTDs)
- Thermistors
These devices are used to measure temperature in various applications.
What is speed of response in a temperature controller?
The time it takes for a controller to react to a change in temperature
A faster speed of response allows for better control over temperature fluctuations.
Explain the difference between controller resolution sensitivity and controller operating differential.
Resolution sensitivity refers to the smallest change in input that the controller can detect, while operating differential is the range of temperature over which the controller operates before switching states.
Understanding these concepts is crucial for precise temperature control.
Explain the thermocouple operating principle.
A thermocouple generates a voltage when there is a temperature difference between two junctions of different metals.
This principle is based on the Seebeck effect.
Explain the function of time-proportioning control.
It adjusts the output of a controller based on the time spent in the ‘on’ and ‘off’ states to maintain the desired temperature.
This method is useful for controlling temperatures in systems with variable loads.
What size of loads can be handled with a relay output controller? Can this load capacity be increased? If so, how?
Relay output controllers typically handle small to medium loads. Load capacity can be increased by using contactors or relays with higher ratings.
This allows for controlling larger devices or systems.
If the band width in an 800°F temperature controller is set for 2%, what is the band width in degrees?
16°F
Calculated as 2% of 800°F.
Explain how the mechanical-link temperature switch operates.
It uses a mechanical linkage that expands or contracts with temperature changes to open or close an electrical circuit.
This type of switch provides a simple and reliable method of temperature control.
What are the disadvantages or problems found in the use of a liquid-filled sensing element as used with a temperature switch?
Potential for leakage, slower response time, and limited temperature range.
These factors can affect the reliability and accuracy of the temperature measurement.
Draw the symbols for a normally open and normally closed temperature switch contact.
Normally Open (NO): (symbol)
Normally Closed (NC): (symbol)
Symbols are important for schematic representations in electrical diagrams.
What is the approximate millivolt output of a type J thermocouple at 500°F?
Approximately 20 millivolts
This output is specific to type J thermocouples and can vary with temperature.
On what principle does the bimetal type of temperature switch operate?
Uneven expansion of two different metals when heated
This principle allows the switch to open or close based on temperature changes.
