Fluid Gas Handling

Pulse Width Modulation Control for Solenoid Valves

Pulse Width Modulation Hold Control Methodology for Solenoid Valves - medical device - Parker Precision Fluidics

Pulse width modulation (PWM) is a method of reducing the average power delivered by an electrical signal, by breaking it up into predefined pulses. When utilized to operate direct acting solenoid valves, a PWM signal can result in significant power saving and heat reduction while maintaining the desired pneumatic function. This blog explains the PWM methodology, as it applies to direct-acting solenoid valves, and provides guidance in establishing the appropriate PWM parameters. 

 

 

Pulse Width Modulation Hold Control Methodology For Solenoid Valves - download the white paper - Parker Precision FluidicsThis blog is part three of a three-part series that comprises a complete white paper "Efficient and Effective Direct Acting Solenoid Valve Control: The Benefits of Using Hit and Hold Electrical Control on Direct Acting Solenoid Valves". Download a copy here.

 

 

 

Figure-14

Pulse Width Modulation Hold Control Methodology for Solenoid Valves_Hit and Hold Curren Valve State Graph - Parker Precision Fluidics

The arbitrary parameters illustrated above in Figure-14, describe two continuous hit and hold current values being supplied to the valve, (IMax) and (I5) respectively. In order to deliver the two separate input current levels, the power supply must be variable or the system must have two independent supplies delivering (IMax) and (I5). Given that both options are not ideal from a cost and power efficiency standpoint, the same power-saving gains can be realized by using a single/continuous DC power supply and adding a PWM, (pulse width modulation) circuit. The following example explains this concept in greater detail.

In the prior example, (Figure-14), a continuous 100mA signal is applied to the valve prior to implementing the 50mA continuous, power saving, signal. In order to implement an equivalent PWM power saving system, the same/initial 100mA continuous hit signal is required to ensure the actuation of the valve. Once actuated, a 50% duty cycle PWM 'hold' signal can then be applied to obtain the equivalent power savings. Figure -15 illustrates the hit and PWM hold scenario described above.
 
Figure-15

Pulse Width Modulation Hold Control Methodology for Solenoid Valves_Hit & Power Hold Current -Parker Precision Fluidics

The average power consumed in this example can then be calculated by multiplying the square of average current, (IMAX x % duty cycle), by the coil resistance. {PAVG = IAVG2 x R = (0.100s x 0.50)² x 136 Ω = 0.34 W}.

End users should be aware that, although the theoretical/calculated hold power is equivalent in each case, (continuous supply and PWM), the actual power consumed at drop out may vary slightly. Therefore, it is important for the end-user to characterize the drop-out parameter utilizing the selected power saving method. Specific to the PWM method, this can be accomplished by simply reducing the duty cycle of the PWM hold signal until the drop-out condition is observed.  

Figure-16 illustrates the output of an arbitrary duty cycle vs. valve state test. In this example, the drop-out condition is observed when the duty cycle is decreased to 40%. It should be noted that the duty cycle step sizes presented in this illustration are course and are intended for explanation purposes only. In practice, the duty cycle step size changes should be no larger than 1%.

Figure-16

Pulse Width Modulation Hold Control Methodology for Solenoid Valves_Decreasing Duty Cycle vs. Valve State - Parker Precision Fluidics

It should be noted that the frequency of the PWM signal illustrated in Figures-15 and 16 is intended for instructional purposes only. Given the fast responding characteristics of a solenoid valve, the frequency of the applied PWM signal must be fast enough to prevent any mechanical oscillation of the armature; to prevent the mechanical components of the valve from chasing the oscillating electrical input signal. Specific to all solenoid valve platforms offered at Parker Precision Fluidics, PWM signals greater than 15KHz are typically recommended to prevent this condition from occurring.

Valve design/type considerations

In the second blog in this three-part series titled: "Capitalizing on Valve Mechanics with a Hit and Hold Circuit", we touched on some of the application parameters which influence the drop-out characteristics of the valve. Of the parameters listed, (vibration, ambient temperature, elastomer compatibility, valve function/porting), valve function/porting is the only parameter which is tied directly to the design of the valve. This parameter is commonly referred to as valve type and given the significant impact of this parameter on drop-out current, it must be considered when creating a test plan.    
 
The solenoid valve operating principles and illustrations presented in this document are representative of a simple 2-way/2-position normally closed type valve configuration. This is a common valve design, which is incorporated into this article to explain basic valve mechanics. Considering the variations in current valve designs and corresponding valve types, (2-way vs. 3-way, mono-directional vs. bi-directional flow, normally closed vs. normally open vs. distributor vs. universal), the scope of this topic is too large to address in this article. Furthermore, if the end-user is unfamiliar with the valve design, mechanical requirements for the valve type, and the corresponding effects on drop-out current, it is highly recommended that they consult the technical support team at Parker Precision Fluidics. Our engineering staff can assist in identifying the appropriate test conditions based on the application requirements and the selected valve design.
 

Pulse Width Modulation Hold Control Methodology For Solenoid Valves - download the white paper - Parker Precision FluidicsThis blog is part three of a three-part series that comprises a complete white paper "Efficient and Effective Direct Acting Solenoid Valve Control: The Benefits of Using Hit and Hold Electrical Control on Direct Acting Solenoid Valves". Download a copy here.

 

Paker Precision Fluidics has been designing and building solenoid valves for over 25 years. Our engineers specialize in helping OEMs update original valves that are producing low yields. Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications. Call 603-595-1500 to speak with an engineer.

To learn more about Precision Fluidics' miniature solenoid valves, download the catalog

 

Capitalizing on Valve Mechanics With a Hit and Hold Circuit - Phil Dodge - Parker Precision FluidicsThis article was contributed by Phil Dodge, senior engineer at Parker Precision Fluidics.

 

 

 

 

 

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