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Latest Silicon pressure sensors show huge improvements

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Latest Silicon pressure sensors show huge improvements

The historical problems associated with silicon oil-filled pressure sensors are well documented. However, recent advances in sensor design has led to improved versions that overcome many of these disadvantages, says Sam Drury, Sales & Marketing Director at Impress Sensors & Systems Ltd.

Historically, oil-filled pressure sensors that use silicon sensing elements have suffered in terms of their measurement performance and reliability due to a number of different factors. However, the latest versions now coming onto the market benefit from much-improved mechanical designs and are therefore able to overcome these drawbacks.

Most silicon pressure sensors are of the media-isolated type, i.e. they operate by using an isolated diaphragm. When measuring pressures, this diaphragm flexes and transfers the pressure via the oil onto a silicon chip. Compared to the latest sensor designs, traditional oil-filled, isolated diaphragm, silicon pressure sensors used a much higher volume of oil.

Whilst the cost of this oil is generally not an issue for users, the effects this oil has on the overall performance and thermal stability of the sensor is a critical design factor. With traditional designs, air often penetrates the housing and becomes trapped within the oil, which can cause problems. As the sensor’s operating temperature flucuates, the physical propoerties of the oil change as the air within it expands or contracts, which leads to measurement errors. Over time, as the sensor becomes less airtight, more air will enter the chamber and the problem worsens.

In order to solve these issues, the latest silicon pressure sensors use much-improved mechanically-sealed designs, which use only a fraction of the volume of oil compared to previous versions. This means that even if any air does get through to the oil, there is less oil and so the effects of temperature fluctuations on the oil are much less, which results in more reliable measurement performance and improved thermal stability. The effects are not completely eliminated but are greatly reduced compared to conventional versions. This means the latest sensors with improved mechanical sealing are now suitable for use in vacuum conditions.

Higher overpressures are also now possible. Typically, the latest silicon pressure sensors offer five times overpressure when operating at 1bar and above, which is much higher than devices on the market and therefore offering customers added security that the sensors will last even in an over pressure state on their system. Similarly, for pressure ranges below 1bar, the latest sensors typically provide 10 times overpressure therefore protecting the sensitive low range diaphragms.

Accuracy is also improved to less than ± 0.1%, which compares very favourably with traditional sensors. There are similar improvements in resolution, repeatability and thermal stability of the sensor.

Oil-filled silicon pressure sensors with an all-stainless steel construction can also be used in food and beverage processing. The latest sensors operate with food-grade oils and due to their improved sealing, are resistant to frequent washdowns, chemicals and other cleaning detergents.

In the past, oil-filled silicon pressure sensors have suffered from orientation issues. For example, if a sensor is factory calibrated to 4mA in the horizontal position, but in the application, is then mounted at an angle or becomes slightly offset, the changes to the physical properties of the oil (due to gravitational effects) may affect the sensor’s measurement performance. The latest versions, which use significantly less oil, do not suffer to the same extent and the effects of gravity on the oil are greatly reduced.

There are many reasons why users select silicon pressure sensors over alternative pressure sensing technologies. Here are some of the technical advantages:

  1. Perfect Elasticity
  2. Low Hysteresis
  3. Great Repeatability
  4. High Gauge Factors giving high output signal
  5. Compact and Lightweight
  6. Acceleration, high vibration and impact shock resistant
  7. Superb Stability
  8. High Over pressure capability
  9. Dynamic Response for fast acquisition applications

Please click here to see the products available in this range of silicon pressure sensors.

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