Wednesday, 28 September 2011

Tiny pressure transmitter

Festo has launched a compact pressure transmitter module providing a very flexible solution for closed-loop control and monitoring of pneumatically-operated automation components. Capable of sensing both pressure and vacuum, the new SPTE pressure transmitter is a highly versatile and easy-to-use feedback device. Typical applications include vacuum detection in pick-and-place machines, such as those used in semiconductor chip testing, and surface-mount component placement machines for PCB assembly.

Designed primarily for cost-sensitive high volume applications, SPTE is the smallest pressure transmitter in theirproduct range. It has a grid size of just 10 mm, facilitating extremely tight packing densities in crowded control racks, and a very low weight which makes it ideal for integrating directly with moving machine parts. The transmitter's extremely small physical dimensions also mean that it has minimal internal volume, enabling it to react quickly to changes in pressure and provide a fast response output signal.

The SPTE uses a piezo-resistive pressure cell capable of measuring vacuum over the range 0 to -1 bar and pressure over the range 0 to 10 bar. The pressure transmitter is available with a choice of 0 to 10 V or 1 to 5 V analogue output, enabling users to employ the control scheme of their choice without need for conversion circuits - the signal can be fed direct to a PLC or other form of control system, helping to minimise installation costs.

A unique benefit of Festo's SPTE pressure transmitter is that it offers users considerable flexibility in mounting, with a choice of three configurations featuring different pneumatic connection schemes.

One configuration, available in 4 mm and 6 mm sizes, enables the transmitter to be plugged directly into pneumatic socket-type connectors. Another provides push-in fittings for standard pneumatic tubing and is available in 3 mm and 4 mm sizes. This form of transmitter module can also be used in conjunction with single and 8-way mounting brackets, which use a simple clip retaining mechanism to facilitate fast assembly and disassembly without the need for tools. The third type of configuration uses a highly cost-effective flange-mounting arrangement, which requires no additional hardware. The module is secured direct to the body of the pneumatic component that it is monitoring - such as a cylinder or valve - and uses an O-ring seal to secure an air-tight connection. By dispensing with the need for pneumatic tubes this approach provides the shortest path between the component and transmitter, minimising evacuation time and resulting in the fastest possible signal generation.

Typically, high throughput pick-and-place machines use any array of tightly packed vacuum gripper nozzles of various sizes, depending on the types of parts to be moved. Each nozzle may require a different vacuum level, the presence or absence of which indicates whether or not a part has been successfully picked. Due to limited space, it is often impractical to use sensors with built-in teach functions to determine the performance of each nozzle at its point of use. By using SPTE pressure transmitters to monitor the vacuum levels, the various thresholds can be defined on the control unit.

Festo's SPTE pressure transmitters are supplied complete with a 2.5 m cable for electrical connection. Designed for operation with filtered compressed air, the transmitters have a full-scale accuracy of 3 percent, and accommodate media and ambient operating temperatures over the range 0 to 50 degrees Celsius.

If required, the SPTE pressure transmitter can be combined with a Festo SVE4 signal converter to produce two digital output signals for applications where an analogue input is not available or cost-effective within the control unit. This arrangement can be used, for example, to monitor upper and lower operating limits.

The SPTE pressure transmitter is a direct result of Festo's on-going research into all-electronic, contactless sensors; in recognition of the advances that the company is making in this area, the product received an honourable mention in the Red Dot Design Awards for 2011.

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