Minimum requirements for solenoid selection.
The following are needed as a minimum to enable solenoid selection
| Function required: |
pull / push / rotary/ latching / locking / etc |
| Stroke movement: |
travel in mm / inches |
| Force needed: |
Newtons / Kgf / Pounds / etc |
| Duty cycle: |
on time / off time ratio |
| Power supply: |
voltage / AC or DC |
| Additional information to assist in making a solenoid selection |
| Operating life: |
how many cycles |
| Environment: |
ambient temperature / wet or dry / clean or dusty/ vibration / etc |
| Installation factors: |
space envelope / mounting preference / plunger design |
| Power supply factors: |
any power (Watts) or current (Amps) limitations in the system |
|
| Solenoid construction |
When selecting a solenoid it is useful to know something about the basic features and characteristics :
- A solenoid is a linear actuator in which, when the coil is energised, the armature (plunger) is Pulled in to the pole piece (stop).
- If a Push function is wanted, then a non-magnetic push-rod is required – see Fig 1.
- Rotary solenoids are selected in much the same way, except that instead of a linear stroke, there is an arc of rotation.
- Generally the force increases as the armature closes on the pole piece – see Fig 2.
- The Duty Rating (%) defines the power of the coil in the solenoid and is the ratio of the ON time to the total time per cycle of operation.
| Duty Cycle = |
time ON
|
X 100% |
|
|
(time ON + time OFF)
|
Examples
- a Continuously Rated (100%) coil may be energised indefinitely but has a lower power consumption resulting in lower magnetic force
- a Short-Rated (e.g. 25%) coil has more force but must be switched off for part of the cycle
Further details and technical definitions can be found in Technical Explanation GXX |
| Fig 1. Linear solenoid, bearing construction |
Fig 2. Force Characteristic |
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| AC solenoid vs DC solenoid? Pro’s & cons : |
AC solenoids
- have an in-rush current, providing high initial stroke force
- can utilise longer strokes than DC solenoids for the above reason
- may hum in operation, according to the application conditions
- the armature (plunger) must always be allowed to seat, otherwise over-heating of the coil may occur.
DC solenoids
- are generally quieter in operation
- have longer operating life (bearing construction versions)
- any DC Solenoid can be operated from an AC supply via a simple bridge-rectifier, also available from us – ask for details.
|
| Other solenoid types |
There are many other variations in solenoid design which may incorporate features such as
- 2 coils & 2 pole pieces
- permanent magnets
- different force/stroke characteristics ; proportional, decreasing
Details on these and many others can be found in the product-specific data sheets, or contact us on 01483 794700 or contact a technical expert. |
