Position sensing is offered on several models of Acro Associate’s pinch valves. Position sensing supplies electronic feedback on a valve's position (OPEN or CLOSED). This feedback confirms that a valve is in the state dictated by a control input. In addition to switching LEDs or sending error messages, a key benefit of position sensing is that it facilitates closed-loop control: subsequent events in a system may be triggered based on a valve's actual state, not a state predicted from an input command.

Depending on their type of output, position sensors are classified in one of two ways: analog or digital. An analog sensor outputs a signal that varies with valve position. For example, as the valve translates from the CLOSED to the OPEN state, the sensor's output voltage may vary from 4.0V to 9.5V, passing through an infinite number of different voltages in the process. By contrast, a digital sensor produces only two outputs. In the earlier example a digital sensor might switch from 0V to 10V as the valve moves from CLOSED to OPEN, with the switch point occurring at 50% of the valve's stroke (the switch point is adjustable and is set at the factory). The decision to use an analog or digital sensor depends on the application, the manner in which the feedback will be processed, and the accuracy required of the feedback.

In addition to the type of output, position sensors may also be classified by type of sensor. Acro Associates offers two types of sensors: Hall Effect sensors and Microswitches.

A Hall Effect Sensor, or Hall Sensor, senses the strength of a magnetic field and outputs a voltage according to that strength. The magnetic field is generated by a permanent magnet that is
incorporated with the pinching mechanism. As the valve changes state, the permanent magnet travels toward or away from the stationary Hall sensor, causing its output to adjust accordingly. Hall sensors are available with either analog or digital outputs, both of which require a 3-wire interface: power, ground, and output. Supply voltage is 0 to 30 VDC while current draw averages 13mA and peaks at 30mA.

In contrast to Hall Sensors, which may be analog or digital, Micro switches are inherently digital as they have only two states, OPEN and CLOSED. A mechanical connection links the state of the switch to that of the valve. The location at which the Microswitch changes state is adjustable but must be near the end of the valve's stroke to prevent over travel and damage to the switch. Microswitches feature three solder terminals - common, N/O, and N/C - which make normally-open and normally-closed configurations possible. Acro offers several types of Microswitches, all having different electrical ratings. Please contact Acro for information regarding minimum and maximum voltage and current specifications.

Position sensors are typically mounted to the ends of valves and add approximately 1" to their overall length. Both analog and digital types of Hall sensors are potted inside an aluminum enclosure to prevent contamination. For applications requiring position sensing and the noise control of a dashpot, a Hall sensor may be fitted to the outside of the dashpot.

To learn more about position sensors or to discuss which type of position sensor would best suit an application, please contact an Acro Applications Engineer either by e-mail or at 1-800-672-2276.