15 - LIMIT/END SWITCHES

Question 1

What is a Limit/End Switch?

Answer 1

A limit switch is a switch operated by the motion of a machine part or the presence of an object. A limit switch can be used for controlling machinery as part of a control system, as a safety interlock, or as a counter enumerating objects passing a point.

Question 2

How does a Limit/End Switch work?

Answer 2

A mechanical lever, roller, plunger, or whisker is used to detect mechanical motion and open/close electrical contacts to control a circuit.

Question 3

How to determine adjustment requirements

Answer 3

Reference mfg specs or given situation in which limit switch is present.

Question 4

What constitutes high resistance

Answer 4

OL / Check mfg specs

Question 5

What are roller or lever arms, how to determine they are faulty or replace them

Answer 5

Roller/level arms are the component on the switch used to detect mechanical motion. The roller is the wheel on the end, the lever arm is the physical lever itself. If the lever is unable to register mechanical motion, it is faulty and must be replaced.

Question 6

What is a stop or cam

Answer 6

A stop is present to limit the range of motion for the lever arm. The cam converts the rotary motion of the lever into linear motion, which then depresses the plunger and closes/opens the electrical contacts.

Question 7

Limit switch bracket mount, what is it

Answer 7

The method used to secure a limit switch in place, subjective to each given switch

Question 8

How to conduct an examination of a limit switch, or determine it has failed

Answer 8

Depress switch and check resistance on contacts. If the contact is NO and displays high resistance / OL, the switch has failed. Vise versa for NC contacts.