Glossary of Technical Terms

A list of terms and definitions you may find helpful.

Duty Cycle (ED)

The duty cycle is expressed as a percentage and represents the proportion of time a solenoid is powered. If a solenoid is energised for 15 seconds and switched off for 45 seconds before being powered again, then the total on/off cycle time is 60 seconds, expressed as a 25% duty cycle.

If the energised period is continuous, the solenoid must be rated at 100%. The duty cycle is based on a standard ambient temperature of 35°C and a chosen voltage.

Many solenoids come with a 100% duty cycle ideal for most applications. However, if your requirement requires a greater force for shorter periods, the duty cycle can be modified to provide the energy the application needs.


Force measurement is in Newtons. Once energised, a solenoid will develop a force to start the movement of the plunger, defined as the pull-in force.

As the plunger moves, the force available will increase until the maximum power is at the end of a stroke. This is the force of the solenoid shown in our technical data.

Other forces include the holding power of bi-stable solenoids with the armature in a home position at the start. The available strength may depend on the mounting orientation and if a return spring is being used.

Force output is affected by temperature. The higher the temperature, the lower the force. The quoted torque or force figures are given at 90% of the rated voltage and with a warm winding. The value is significantly higher with a cold winding and the rated voltage. Rotary solenoid output is defined as available torque. Note: 1 Newton = 0.1Kgf = 0.225 lbf.


You should specify the operating voltage of your solenoid; most solenoids are DC.

A solenoid can be overvolted to achieve a more significant force; however, the overvoltage will create additional heat, thus reducing the duty cycle. For example, a 24V DC wound coil might be overvolted by 300%, but only for milliseconds.


In solenoid construction, power is usually defined as the rate of energy transfer expressed in Watts. In solenoids, it establishes the amount of energy/power available to do work.

The power transfer required to achieve a (mechanical) force output will be very much the same irrespective of operating voltage, but the current consumption will vary.

The current defines the wire size used in the coil windings and will affect the solenoid’s electrical driving circuit.

A solenoid may draw more power when moving from rest than in its holding position.

Life Expectancy

Life expectancy for solenoids is dependent more on the application than on the design of the solenoid itself.

Temperature, loads, moving positions, and operation frequency will all affect a solenoid’s total life expectancy.

Typical standard solenoids have operating lives of 107 - 108 cycles, with heavy-duty designs capable of 1012 cycles, but this is a guideline only as the solenoid is part of a more complex mechanism.


The standard solenoid reference temperature is an ambient 35°C. The warm operating condition is when a steady temperature is reached.

The effect of temperature on a solenoid is significant. For example, a solenoid rated for a 100% duty cycle generates 80% force if the ambient temperature increases to 50°C.

Pull in Time (Actuation Time)

The total time it takes from switch-on to when a linear solenoid completes its stroke or a rotary solenoid has moved through its rotation angle.

Included is the coil excitation time. It is sometimes possible to reduce overall pull in time by over-exciting (overvolting) the coil for a short period (milliseconds).

Drop Out Time

The total time the solenoid returns to its resting position after the current is switched off. The drop-out time depends on the mass moved and the influence of any springs. Drop-out times are not shown in our data tables.


Torque is the power output of a rotary solenoid, usually measured in Newton centimetres (Ncm).

Solenoid torque is measured at 90% of the rated voltage and with warm windings (see force). A rotary solenoid has a set angle of travel, usually 25°, 35°, 45°, 65° or 95°. The highest torque is at the end of the movement.

Operation Frequency

Cycle rate usually per minute or second made up of on-time and off-time. It has a bearing on the duty cycle and life expectancy.

Surface Preparation

The standard surface finish is galvanised zinc. For special finishes, please ask.

IP Rating

An IP rating is a two-figure code number, for example, IP40, the first digit being the degree of protection against the ingress of solids and the second digit being the degree of protection against water.

Plunger or Shaft

The armature on the energisation of the coil moves the plunger or shaft.

Most solenoids can be customised to suit each application with individual shaft threads, chamfers, slots, and flats.


The part of the solenoid which moves within the magnetic field generated by the coil.

It is separated from the coil by the minimum air gap possible. Armature systems vary, combining flat faces and conical shapes to achieve different stroke/force combinations.


The winding of many turns of fine wire around a hollow core, which, when energised by the current, will develop a magnetic field inside the body.

In solenoid design, the coil is defined by the specific operating voltage for a given duty cycle.

The more opportunity for the coil to remain cool, the greater the number of turns that can be wound onto any single spool.

This way, a stronger magnetic field is developed to achieve higher operating forces and torques; similarly, the current measured in mA is higher for any given voltage if the duty cycle % is low.

It is possible to overvolt a solenoid beyond its specified voltage, in which case a stronger magnetic field is developed with quicker pull-in times achieved. But this can only be done under strict control for short periods (ms); otherwise, the coil will likely be permanently damaged.

Frame or Body

There are different body shapes or frame types. Some design aspects affect movement, mounting and the available space envelope.

Check out the difference in design on these pages from the smallest open-frame linear solenoids used for many locking vending machines to the heavy-duty E series rotary solenoids and RM heavy-duty linear solenoids.

Silicon Bridge Rectifier

Most solenoid applications use DC, allowing compact design, long life, accuracy and versatility.

If the application may be one where only AC is available, it may be possible to use a silicon bridge rectifier. A 230V AC supply, for example, operates from a 205V DC wound coil in this way.

The coil is still DC, but the application is AC. Using a silicon bridge rectifier gives all the benefits of a DC coil without the disadvantages of an AC.