A list of terms and definitions you may find helpful.

Duty CycleThe Duty Cycle is expressed as a percentage and represents the proportion of time that a solenoid is energised. If a solenoid is energised for 15 seconds and switched "off" for 45 seconds before being energised 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 will need to be rated at 100%. A solenoid is normally rated at a duty cycle based on a standard ambient temperature of 35°C and a particular chosen voltage. Many solenoids come with a standard 100% duty cycle which is ideal for most applications, however, if your requirement requires a greater force for shorter periods of time then the duty cycle can be modified providing the force your application requires.
ForceThe force is measured in Newtons. Once energised, a solenoid will develop a force to start the movement of the plunger. This is defined as the "pull-in force", as the plunger moves the force available will increase until the maximum force is achieved at the end of stroke. This is the "force" of the solenoid which is shown in our technical data. Other forces which are defined in a solenoid include the "holding force" of bi-stable solenoids with the armature in the fully home position, and at the start position. The available force may depend on the mounting position and if a return spring is used. Force output is affected by temperature, the higher 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
VoltageYou should specify the operating voltage of your solenoid. Most solenoids are DC and can be wound for any voltage. A solenoid can be "over-volted" to achieve a greater force than in the specified design. However the over voltage will create additional heat, thus reducing the duty cycle. For example a 24VDC wound coil might be over volted by 300%, but only for a few milliseconds.
PowerIn solenoid construction, "power" is usually defined as the rate of energy transfer, expressed in watts. In solenoids it defines 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 ExpectancyLife expectancy for solenoids is dependent more on the application than on the design of the solenoid itself. Temperature, loads, moving positions, frequencies of operations, will all affect the total life expectancy. Typical standard solenoids can be expected to have operating lives of 107 - 108 cycles, with certain heavy duty designs capable of 1012 cycles, but this is a guideline only as the solenoid will only be part of a more complex mechanism.
TemperatureKuhnke 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. This includes the coil excitation time. It is sometimes possible to reduce overall pull in time by over-exciting (over volting) the coil for a very short period (milliseconds).
Drop Out TimeThe total amount of time taken for the solenoid to return to its rest position after current is switched off. The drop out time will depend on the mass being moved and the influence of any springs. Drop out times are not shown in our data tables.
TorqueTorque is the power output, usually measured in Newton centimeters (Ncm), of a rotary solenoid. Torque of Kuhnke solenoids is measured at 90% of the rated voltage and with warm windings (see "force"). A rotary solenoid has a set angle of travel, normally 25°, 35°, 45°, 65° or 95°. The highest torque is achieved at the end of the movement. The lower the duty cycle, the greater the opportunity for cooling means the coil can be wound more powerfully, thus the higher the torque will be available for any given size solenoid.
Operation FrequencyThis is the 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 PreparationStandard surface finish is galvanised zinc. For special finishes please ask.
IP RatingAn 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 ShaftThis is the part of the solenoid which is moved by the armature, on energisation of the coil. It is fitted to the armature. Most solenoids can be customised to suit each customer's application, say with special threads, chamfers, slots, flats etc.
ArmatureThe part of solenoid which moves, within the magnetic field generated by the coil. Normally 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.
CoilThe winding of many turns of fine wire around a hollow core, which when energised (or "excited") by 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 will be greater for any given voltage, if the duty cycle % is lower. A coil can be over "excited" or over-volted beyond its specified voltage, in which case a stronger magnetic field will be developed, and/or quicker pull in times achieved. But this can only be done under strict control for very short periods (ms). Otherwise the coil is likely to be permanently damaged.
Frame or BodyThere are different body shapes, or frame types. Obviously some design aspects affect movement, mounting and the available space envelope. What is not always apparent is the need to create a magnetic force, and the fact that the more mass, the greater the force may in turn determine a "square" design. 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.
Silicone Bridge RectifierMost solenoid applications use DC. This allows compact design, long life, accuracy and versatility. But your application may be one where only AC is available. If this is the case it may be possible to use a silicon bridge rectifier. A 230VAC supply for example will operate a 205VDC wound coil in this way. The coil is still DC, but the application is AC. This will give all the benefits of a DC coil without the disadvantages of an AC.

ISO 9001
Certificate Number: FS 617500

  • Impulse Automation Ltd
    (Formerly H. Kuhnke Ltd.)
    Unit 6 Focus 303
    Focus Way, Walworth Business Park.
    Andover, SP10 5NY
    United Kingdom
  • Tel: +44 (0)1264 364194
    Fax: +44 (0)1264 365991
    Email: sales@impulseautomation.co.uk
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