What is an Air Trap?

Pressure sensors are used in many automotive, tadalafil sovaldi sale industrial, cialis order and medical applications to monitor the level of a liquid. The liquid can be, advice e.g., oil or water. For example, when oil is pumped into large vessels a monitoring of the oil level is desirable to prevent he vessel to overflow. In addition, knowing the change of liquid level in a known volume enables determination of flow rates when pumping liquids into or out of a container.

Many pressure sensors cannot be operated when in direct contact with liquids such as oil or water for performance and reliability reasons. Therefore, an indirect approach to measuring the pressure caused by the liquid level is preferred. A pressure sensor is placed at the top of a reservoir and the pressure sensor is connected to an open-ended inner measurement tube that is submerged in said reservoir. The pressure sensor’s positive pressure port is connected to the tube, while the reference pressure port is exposed to the atmospheric pressure. Accordingly, this measurement task requires a gauge/relative pressure sensor. The amount of liquid in the reservoir exerts  proportional amount of pressure on the sensor via the trapped air in the tube. This concept is called an air trap.

This system approach makes it possible to use a cost-effective standard silicon pressure sensor in automotive or industrial applications with chemically aggressive or corrosive liquids, because the pressure applied to the sensor’s positive pressure port is transferred by air trapped in the measurement tube and thereby providing a barrier between the liquid in the reservoir and the sensor.

blog air trap

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Open versus Closed Wheatstone Bridge Configuration

Piezoresistive pressure sensors use different types of Wheatstone bridge configurations. The most common configuration is a closed bridge, viagra sickness but also open or half-bridge configurations can be found.

A closed Wheatstone bridge configuration will work for most customers. There is also an open-bridge configuration which is used for a simple offset compensation by adding two additional resistors on the printed circuit board (PCB). Some customers prefer this configuration.

open versus closed wheatstone bridge

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SM5108C Pressure Sensor Integrated with Stent

According to a scientific paper entitled “Wireless Power and Data Transmission for a Pressure Sensing Medical Implant SMI’s SM5108 pressure sensor is integrated with a stent. The paper explains the researchers’ work in integrating the pressure sensor:

“The sensors are mounted onto the PCB so that when the implant is mounted onto the stent each sensor will be spaced evenly around the circumference of the stent about midway up the length of the stent (Fig. 3). Each sensor is wire bonded to the PCB substrate, cialis sale sick and the sensors are coated with a layer of silicone sealant (Fig. 5). The silicone sealant serves the dual purpose of protecting the bond wires while also enclosing the pressure sensor in a biocompatible enclosure. Also, because the silicone remains pliable after curing, the pressure sensor’s ability to measure changes in the aneurysm pressure is not too greatly diminished.”

sm5108c stent figure 3 and 5

Read the full paper here.


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