The Smart Pressure Device SPD series of pressure sensors are silicon based and encapsulated in all kind of housings. The pressure range can vary between about 10 mBar and 20 Bar gauge and differential. In case of an absolute version the reference vacuum chamber is formed on the die during manufacturing. Due to fact that the bridge resistance values, the bridge output pressure sensor is especially suited to use in combination with the Universal Transducer Interface (UTI03).
The Smartec Pressure Devices are based on the principle of bending a membrane caused by the pressure in a liquid or gas. On the membrane is a very thin conductive screened layer that that follows the bending of this membrane. The resistance of the conductive layers will change when the membrane is bended. A smart mechanical layout of four resistive structures can form a stable Wheatstone bridge, comparable with the classical strain gauge sensors.
The bending of the membrane (and also the layer) is very small (<< 1 mm), but is still large enough to measure the changes in the resistive values. The resistive structures on the surfaces can be compressed or stretched depending what direction the membrane is bended. When the layer is compressed the resistance value will decrease and when stretched this value will increase. In practice this means that the Wheatstone bridge is imbalanced in a positive and in a negative way respectively.
In general the screened resistors are also sensitive to temperature which means a compensation for temperature effects is required. For the Smartec pressure sensors this compensation is done in the amplifier to obtain a stable analogue output.
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