Closed loop electro-pneumatic controls

Pneumatic systems & components

1st Quarter 2013 Pneumatic systems & components

Proportion-Air’s electro-pneumatic controls, which have been a staple in the industry for over 20 years, can be electronically reconfigured to accept feedback from its F-Series flow monitors. This combination of components provides a complete flow control package for flow ranges ranging from 0,016–0,16 l/sec to 118 l/sec. Because the feedback is real-time, the series of flow controllers can respond instantly to changes in command or system fluctuations. This fast response allows manufacturers and machine builders to use flow control in applications using high cycle rates.

The Proportion-Air F-series is a line of flow transducers designed specially to provide real-time flow measurement of compressed gases for many demanding applications. It utilises differential pressure (DP) technology to sense the pressure change across an internal venturi. This differential pressure (DP) measurement is fed into an onboard electronic circuit that converts the DP signal into a linear analogue output signal which represents the flow through the F-series.

The DP sensor and circuit are completely analogue in order to offer the fastest possible response time and eliminate the digital stepping often seen in the flow transducers of other technologies. Pipe sizes range from 0,6 to 3,8 cm. Both NPT and BSP threads are available. It has an IP65 housing, 25 G rating, and its large venturi can digest contaminants and moisture. The F-series is also insensitive to mounting position and vibration.

The differential pressure technology is ideally suited for rugged commercial and industrial applications. It allows measurements of flows from 10% to 100% of the maximum calibrated range. The benefits of real-time measurement make the F-series a must in many rapid sequence applications.

The servo valve and flow transducer (our flow control package) are plumbed into a directional valve so that it can control the cap end or the rod end of the cylinder’s speed. Speed is adjustable on the fly with a command signal. Speed is visual unless an LVDT is used and velocity can be monitored via a PLC if required. Repeatability is excellent. If the correct speed is achieved with 5 V d.c., for example, one can be assured that speed results with a 5 V d.c. command will be very repeatable.

Ramped speed is easily achieved as well. So if a ramped command is given to the device, it will track that command with a ramped velocity. This is typically done when throttling back speed just before reaching the end of the actuator’s stroke. Proximity sensors could be mounted on the actuator to the switch signal sent back to the PLC to start the ramp function.

For more information contact Loraine Lundall, FCE Technical Services, +27 (0)12 808 0142, [email protected], www.fcets.co.za

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Closed loop electro-pneumatic controls

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