Latching Solenoids: A Green Solution

Green EarthThere are many definitions of what constitutes a “green” product as well as the variable degrees of “greenness” a product may exhibit. Many consider a product green if it provides superior or even comparable performance to an alternative product while consuming fewer resources to be produced and utilized. The latching solenoid technology designed by TLX Technologies easily falls into this “green” category. TLX’s latching solenoids consume no power, produce no heat and generate no electrical noise while holding in either the on or off position. This technology also provides superior performance over the constantly powered solenoid actuators manufactured by other companies.

Permanent Magnet (PM) latching solenoid actuators utilize permanent magnets in conjunction with the solenoid coil to maintain the position of the plunger with no current applied. The permanent magnet generates a small magnetic flux in the magnetic circuit generating an attraction of the plunger and the fixed pole piece with no power applied. When a short pulse of electrical current is applied to the coil, the resulting electromagnetic flux generated by the coil can either add to or subtract from the permanent magnet flux depending on the polarity of the applied current.

Intrinsically Safe Latching SolenoidIn applications where the load is acting to extend the plunger away from the fixed pole, latching solenoids can maintain the extended or retracted position without consuming continuous power. In applications where there is no load to act on the plunger, a spring can be used to hold the plunger in the extended position. In either case, a pulse of current is applied to generate magnetic flux to add to the permanent magnet and move the plunger to the fixed pole piece. When the current is removed, the plunger is held in the “latched” position by the permanent magnet. Conversely, applying a reverse polarity pulse will cancel the flux of the permanent magnet allowing the load or spring to release the plunger and move to the extended position.

Residual Magnetism (RM) latching solenoid actuators operate in much the same way as permanent magnet latching actuators do. However, there are some unique design differences. While both types of latching actuators maintain the latched position without electrical power, residual magnetism actuators remain latched without the use of permanent magnets. Residual Magnetism Latching SolenoidRM latching actuators offer the same benefits as PM latching actuators by consuming no power, producing no heat and generating no electrical noise while in the latched position. RM latches utilize the inherent “residual magnetism” common to all DC actuators which has been enhanced through special internal design features to provide exceptional latching force without permanent magnets. Latching the RM latch is accomplished by providing a short pulse of electrical current of either polarity to pull-in and latch the plunger to the fixed pole piece. Unlatching the actuator is accomplished by applying a pulse of lower current in the opposite polarity of what was used to latch the actuator. Unlike the PM latching actuators which can be manually latched, RM latching actuators cannot be reset after de-latching without applying a pulse of electrical current.

Both styles of latching actuators are equally “green” and well suited for applications where high speed actuation and long open or close times are desired. The relative power consumption comparison between conventional constant current solenoids and “latching” solenoids is illustrated in the diagram.Constant Current vs. Latching The response time to move the plunger is the same for both solenoids. However, as the conventional solenoid is required to maintain the current (consume power) for the full on cycle, the “latching” solenoid moves with a “pulse” of current and is turned off (consuming no power) for the duration of the on cycle. Conventional solenoids are restricted to generating forces up to a 100% duty cycle and may be subject to heat dissipation problems. The “latching” solenoid can be turned off during most of the on cycle allowing the use of a higher current pulse which produces faster speed operation and generates higher pull force without the excessive power consumption or heat generation of a conventional solenoid. In addition, the possibility of applying a higher current to generate more force may allow for a smaller actuator to be used in an application and offer the potential benefit of overall cost reduction.

While latching actuators can offer performance advantages in a variety of applications, latching actuator technology may not be well suited for use in applications where the actuator is required to “fail” to a known position upon power failure. Since latching actuators need to be powered to change state, the actuator would remain in the position it was in when the power failed. However, it is feasible to include a drive circuit with an energy storage feature in the control circuitry to allow the actuator to be positioned properly in the event of a power failure if desired.

Both PM and RM latching actuators can be custom designed in either open frame or tubular solenoids as push, pull or bi-stable (push-pull) arrangements. They can also be designed in two or three-position configurations depending on the application requirements. In addition, a variety of drive circuits ranging from a simple diode-resistor circuit to the more complex PWM current control circuit can be used to offer the most cost effective and “green” solution for your application problem.

If you are looking for ways to “green” your application, contact our Technical Team to discuss your current or future project needs. TLX Technologies has successfully helped customers improve efficiency, reduce product size and lower power consumption for their applications.


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TLX Technologies LLC will consistently provide products that meet or exceed the requirements of our customers. The company complies with all the requirements of the ISO 9001:2015 Quality Management System Standard and TS16949:2009 where applicable. We will establish, monitor and work to continuously improve customer satisfaction, technology, productivity, quality and employee engagement.