Glossary of Technical Terms

A list of terms and definitions you may find helpful.

Duty Cycle (ED)

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 25% duty cycle.

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

Many solenoids come with a 100% duty cycle which is ideal for most applications, however, if your requirement requires a greater force for shorter periods, then the duty cycle can be modified providing the force that the application needs.

Force

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 force at the end of a stroke, this is the force of the solenoid shown in our technical data.

Other forces include the holding force of bi-stable solenoids with the armature in the full home position, and at the start position. The available force 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. With a cold winding and the rated voltage, the value is significantly higher. Rotary solenoid output is defined as available torque. Note: 1 Newton = 0.1Kgf = 0.225 lbf.

Voltage

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 a few milliseconds.

Power

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.

It is the current which defines the size of wire used in the coil windings, and which will affect the electrical driving circuit of the solenoid.

A solenoid may draw more power when moving from rest than when 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, frequency of operation, will all affect the total life expectancy of a solenoid.

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.

Temperature

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

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

Pull in Time (Actuation Time)

The full time it takes from switch-on to the moment 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 amount of time taken for the solenoid to return to its rest 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

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

Solenoids 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 per second made up of on-time and off-time. It has a bearing on the duty cycle and life expectancy.

Surface Preparation

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

Part of the solenoid which is moved by the armature, on energisation of the coil.

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

Armature

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 face and conical shapes to achieve different stroke/force combinations.

Coil

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 core.

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

The more opportunity there is for the coil to remain cool then the greater the number of turns can be wound onto any given 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 developed with quicker pull-in times achieved. But this can only be done under strict control for short periods (ms); otherwise, the coil is likely to 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 that appears in these pages as you see 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, and this allows 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.