EC ( Control Units ) Ch 3

Question 1

How would you panel mount an oil-tight unit?

Answer 1

Drill a correctly sized hole in the control panel.
• Insert the oil-tight unit from the front.
• Secure it with a locknut or mounting ring from the rear.
• Ensure the gasket or sealing ring is properly seated to maintain the oil-tight seal.

Question 2

Why is a low-voltage bulb preferred in a pilot light?

Answer 2

It will withstand vibration.

Low-voltage bulbs, especially LED types, are more rugged and less prone to filament breakage due to vibration.

Question 3

Symbol for a mushroom-head push-button (1 NO, 1 NC contact)

Answer 3

• Large mushroom cap symbol
• One normally open (NO) contact (open switch)
• One normally closed (NC) contact (closed switch)

Question 4

Are lenses for pilot lights available in more than one color? If so, why?

Answer 4

Yes, lenses come in various colors to indicate different statuses:
• Red – Fault/Stop
• Green – Normal/Go
• Amber/Yellow – Warning
• Blue – Special function
• White – Power ON or neutral

Question 5

Advantage of panel mounting a contact block?

Answer 5

Panel mounting provides space for terminal block installation, allowing neater wiring and easier maintenance.

Question 6

Symbol for a red push-to-test light

Answer 6

• Pilot light symbol
• Circle with a test button indicator (often a T or diagonal slash)
• Label or fill indicating red

Question 7

Symbol for a 3-position, 4-contact selector switch

Answer 7

Position 1: Contacts 1 & 3 closed
• Position 2: All open
• Position 3: Contacts 2 & 4 closed

This would be drawn using:
• A rotary selector with three positions
• Four contacts shown with connection status per position

Question 8

Explain push-to-test pilot light & circuit diagram

Answer 8

Function:
• Normally off when system is off
• Pressing the test button manually completes the circuit, illuminating the bulb to verify it works

Typical circuit:
• 120V source -> switch -> light
• Test push-button in parallel with control circuit to allow manual test

Question 9

Circuit: 2-position selector + green push-to-test pilot light

Answer 9

Function:
• Selector switch in “ON” = pilot light active
• Push-to-test allows checking the lamp without system being ON

Circuit includes:
• Selector switch (ON/OFF)
• Pilot light with parallel test button
• 120V supply and neutral return

Question 10

Problem with first type XYMOX above 65°C?

Answer 10

Material degradation – adhesives or polymers may fail or deform, causing loss of tactile response or electrical contact issues.

Question 11

What makes membrane switches rigid in rigid construction?

Answer 11

Backplates or stiffeners (metal or fiberglass layers) give structural support and prevent flexing.

Question 12

Uses of LEDs in programmable controllers (PLCs):

Answer 12

Status indicators (input/output status)
• Error or fault indication
• Power-on indication
• Communication activity

Question 13

Uses for an annunciator

Answer 13

• Visual/audible alerts for system faults
• Alarm conditions in industrial processes
• Operator guidance for troubleshooting
• Monitoring multiple system points

Question 14

What does liquid crystal material consist of?

Answer 14

Organic compounds that exhibit liquid and crystalline properties – usually nematic molecules with rod-like shapes that align under electrical fields.

Question 15

Three types of liquid crystal display (LCD):

Answer 15

1. Twisted Nematic (TN)
   
   2. In-Plane Switching (IPS)
   3. Vertical Alignment (VA)

Each has unique traits for contrast, viewing angle, and response time.