EC (solenoids) Ch 5 Flashcards
(19 cards)
What is the standard symbol for a solenoid coil?
A coil or rectangle labeled ‘SOL’ or similar, often shown connected in a control circuit.
A visual diagram may be helpful for better understanding.
What happens if the plunger is prevented from completing its stroke?
The coil draws excessive current continuously, leading to overheating, possible burnout, and reduced lifespan.
At what position of the solenoid plunger does inrush current appear?
When the plunger is fully extended (initial position), before movement, when magnetic flux is low and inductance is minimal.
Why must solenoid pull always exceed the load?
To ensure reliable actuation and complete plunger travel for full mechanical motion and electrical control.
What happens if solenoid operation exceeds its design?
Overheating, premature failure of coil insulation, reduced performance or erratic actuation.
What happens to the valve spool when a spring-return solenoid is deenergized?
The spring pushes the spool back to its original or default position.
What components are included in a control circuit with a solenoid?
2 push-buttons, control relay, solenoid.
What is solenoid current with the plunger closed?
Sealed or holding current, which is lower than inrush current because inductance is higher with plunger closed.
What happens to the spring in a single-solenoid, spring-return valve when the solenoid is energized?
It is depressed (loaded) as the solenoid compresses the spring during actuation.
What causes the force on the solenoid plunger?
A magnetic field that is produced about the coil.
What is the difference between a proportional and an ON/OFF DC solenoid?
ON/OFF solenoid is binary – fully on or off; proportional solenoid allows variable plunger movement based on input current.
How can you move the spool more or less in a proportional solenoid?
By varying the input current: more current = more force = greater spool movement.
How is force direction reversed in a force motor?
By reversing the polarity of the current, changing magnetic field direction and thus reversing motion.
Describe the force/current relationship in a proportional solenoid vs. a force motor.
Proportional solenoid has a linear relationship over a range; force motor is more precise and linear over wider ranges with feedback.
What happens if a solenoid is overvolted for long periods?
Excessive heat buildup, insulation breakdown, failure of coil or surrounding components.
Compare inrush vs. holding current in DC-operated AC solenoids.
Inrush and holding current are equal in pure DC solenoids; AC solenoids have higher inrush due to inductive properties.
Why use shading coils when a DC solenoid is used on AC?
Shading coils reduce coil buzzing and help maintain the magnetic field during zero crossings in AC, preventing chatter.
What are two methods to measure solenoid temperature rise?
- Direct temperature measurement (with thermocouple or IR)
- Resistance method (measure resistance change due to temperature).
Which method is more practical for measuring solenoid temperature rise?
Resistance method, especially for built-in/encapsulated solenoids.
