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1. Explain how a mechanically operated device works.
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2. What are the three basic components of a limit switch?
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Motor Control ch 3

Automatic Pilot Devices

QuestionAnswer
1. Explain how a mechanically operated device works. opened or closed by the physical contact between a moving part.
2. What are the three basic components of a limit switch? body, operator head, actuator
3. Limit switches are ____ devices that are activated by ___ contact with a moving object. mechanical, physical
4. Limit switches must be selected for the right application and mounted correctly. Name four installation guidelines that will aid in limit switch installations. 1)Mount them rigidly and in easily accessed locations. 2) Never mount where heat exceeds specified limits. 3) Provide adequate clearance for easy service and replacement. 4) Mount switch bodies so cover plates face maintenance access points.
5. A correctly installed limit switch permits allowed-travel and prevents ___. over travel
6. Name four limit switch actuators. lever, fork lever, wobble stick, and push rod.?
7. A sub class of limit switches, micro switches have similar ___ and ___ characteristics. physical , electrical
8. Miniature switches are often used in equipment enclosures to detect ___ and ____. open panel doors, missing equipment guards.
9. The force applied to the actuator required to operate the switch contacts is called ___. operating force
10. Define total travel position (TTP) position of actuator when it releases the stopper.. check my answer page 10
11. Name four automatically operated input devices that are triggered by a change in a process. liquid level, pressure, fluid flow, and material temperature
12. 15 and 19 Need to draw something
13. Give three examples of where a flow switch might be used. boilers, cooling lines, and air compressors. also fluid pumps
14. A discrete switch (ON/OFF) used to control the level in a tank or a bin is called a ___ or ___ switch. level or float switches
16. Briefly describe the operation of a mercury bulb type float switch. Electrical contacts are inside the bulb. The bulb floats on liquid in the tank. If liquid drops, the bulb turns vertical and closes.
17. Name the three categories of pressure devices. diaphram, bellows, and piston
18. When would a positive pressure switch be actuated? When there is an increase in pressure compared to atmospheric pressure
20. In your own words, define deadband. An area with a signal range where no action occurs.
21. Pressure and temperature devices utilize ___ control more often than other types of automatic control. deadband
22. What are the three most common pressure sensing devices and their pressure ranges (low, medium, and high) diaphragm is low pressure, Bellows is medium, piston is high
23. Name three frequently used mechanical temperature sensing devices. bimetallic strip, capillary tube, and direct immersion probe
24. Briefly describe how the bimetallic strip temperature sensing device operates. Made of 2 metals with different rates of expansion and contraction. It bends when temperature changes and opens or closes contacts.
25. Describe how the capillary tube temperature device operates. Has a bulb, tube, and bellows all filled with liquid. The fluid volume increases as the temperature increases. This pushes the bellows and opens the contact. page 52 text
26. Name the two categories that limit switch problems can be grouped in. operator problems and contact problems
27. List three conditions that may cause a sticking or sluggish operator. Dirt on mechanical linkages, improper adjustment of linkage arms and cams, corrosion of bearings in rotational linkages and mechanisms.
28. If all parts of the pressure control circuit are good except for the ___, then troubleshooting the ___ is necessary. pressure switch, pressure switch
29. The ___ for temperature switches are easy to access since only the capillary tube bulb is in the process system. operators
Created by: JoshHampton
 

 



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