Solenoid Pinch Valves Pulse and Hold - Acro Associates - #1

ACEP

Innovators in Fluid Control Systems

Acro Associates' solenoid pinch valves employ a spring-loaded linear actuator to control motion of the pinching surfaces. Most

linear solenoid actuators are closing-the-air-

gap devices, where the force characteristics vary substantially throughout the stroke. Generally, actuators are designed so that the

force to power ratio increases by a factor of

3^4 as the unit moves towards the fully energized position. Utilizing these characteristics of solenoid actuators, the "Pulse and Hold" technique can hold a pinch

valve in the energized state at reduced power with respect to applied power required for initial activation. Power consumption is optimized, heat generation minimized and the

result is increased performance: higher actuation forces, longer strokes, extended

duty cycles and longer on times.

A solenoid actuator can be modeled as a fixed resistance in series with a variable inductance (an RL circuit). Resistivity of the wire used to wind the solenoid's coil determines the DC resistance of the solenoid. The arrangement of the windings and materials used to construct the actuator, in addition to the position of the ferrite plunger (or core), determine inductance of the solenoid. Because the solenoid is resistive, any current

passing through the windings produces heat.

Excessive heat may damage the actuator and consume unnecessary power. In general,

power management devices, such as Acro's

Model 900R, modulate output current to the

device, so that desired mechanical performance is achieved, while significantly

reducing energy consumption and waste-heat

production.

"Pulse and Hold" (also known as "Spike and

Hold", "Pick and Hold", and "Hit and Hold") is a technique whereby a strong, short duration

DC pulse is passed through the solenoid actuator to close the air gap; then current is

lowered to an appropriate hold level. In the hold state, Acro's Model 900R controller

operates the power switch in PWM mode and

the reduced current maintains the solenoid's energized state. When the control signal is removed, the power switch shut offs and the cycle ends.

Acro's Model 900R is a rugged, cost effective

control module designed for interfacing high

performance solenoid actuators (such as Acro's Model 904, 955. 958 and 960 solenoid pinch valves) to computer systems and digital logic. Its primary purpose is to provide "Pulse & Hold" actuation, which improves valve efficiency and performance. This allows Acro

to solve difficult pinch valve applications.

1990 Olivera Road, Suite A Concord, CA 94520-5455

E-mail: support@acroassociates.com

Phone: 925) 676-8828 Fax: (925)-680-8113