A brief discussion on the negative pressure issue in pressure sensors

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Pressure sensors used to measure negative pressure or vacuum are commonly encountered. Those who work frequently with such sensors find that the maximum range for measuring negative pressure with these sensors is usually -100 kPa, or -0.1 MPa. However, a very small number of manufacturers claim to be able to measure -300 kPa or even lower. What exactly is going on? Actually, this is an analysis from two different perspectives. Those who have studied physics know that the pressure in a vacuum is -100 kPa. That’s why the lowest pressure that can be measured by ordinary pressure sensors is -100 kPa; this is based on that value. As a result, most negative pressure sensors available on the market are capable of measuring up to -100 kPa at the lowest. So what about sensors that can measure -300 kPa? -300 kPa is not actually based on atmospheric pressure; in physics, a reference point is necessary. You can think of it this way: inside a sealed box, there is high-pressure gas at 300 kPa, and inside that box there is another box that is vacuum. We use a negative pressure sensor placed in the outer box to measure the pressure inside the inner box, and this results in a reading of -300 kPa. That’s how a pressure of -300 kPa is generated. It is not based on atmospheric pressure. Understanding this concept is very helpful when choosing a negative pressure sensor; that’s why, when helping customers select sensors, we first ask about their operating environment and then about the range they require. Only in this way can one avoid choosing the wrong pressure sensor.