EC ( Pressure Control ) Ch 8

Question 1

What does Normally Open (NO) mean in pressure switches?

Answer 1

Closes on pressure rise

NO switches complete the circuit when pressure exceeds a certain threshold.

Question 2

What does Normally Closed (NC) mean in pressure switches?

Answer 2

Opens on pressure rise

NC switches break the circuit when pressure exceeds a certain threshold.

Question 3

What is the definition of Differential in Pressure Switch Operation?

Answer 3

The difference between the cut-in and cut-out pressure

This prevents rapid cycling in systems with fluctuating pressure.

Question 4

List the four major types of pressure switches.

Answer 4

• Diaphragm-type
• Piston-type
• Bourdon tube-type
• Bellows-type

Question 5

What prevents oil leakage past the piston in a piston-type pressure switch?

Answer 5

An O-ring

The O-ring seals the piston to prevent leakage.

Question 6

Why is dampening used with the Bourdon-tube pressure switch?

Answer 6

To reduce pressure pulsations or spikes

This helps prevent false tripping or wear on the mechanism.

Question 7

What is the usual pressure operating range for diaphragm-type pressure switches?

Answer 7

Typically ranges from 0 to 1500 psi

The range depends on design and application.

Question 8

What components are included in the control circuit described?

Answer 8

• 2 Push-button switches: Start (NO) and Stop (NC)
• Relay (CR)
• Pressure switch (NC contact)
• Solenoid valve (SOL)

Question 9

How is switching accomplished in the solid-state pressure switch?

Answer 9

Using semiconductor circuits (transistors, op-amps)

These circuits detect a pressure threshold and control an output.

Question 10

List the four switching configurations in solid-state pressure switches.

Answer 10

• Normally open (NO) output
• Normally closed (NC) output
• SPDT (single-pole double-throw)
• Analog output (e.g., 0–10 V or 4–20 mA)

Question 11

How is the differential resistance in a pressure transducer measured?

Answer 11

By applying a constant voltage to a Wheatstone bridge

The measurement is based on output caused by diaphragm deflection.

Question 12

Fill in the blank: The pressure switch turns on at the _______ pressure.

Answer 12

[cut-in]

Question 13

Fill in the blank: The pressure switch turns off at the _______ pressure.

Answer 13

[cut-out]

Question 14

True or False: A normally closed pressure switch allows current to flow when pressure is low.

Answer 14

True

Normally closed switches are designed to break the circuit when pressure rises.