What are the commonly used terms for pressure sensors?

When it comes to sensors, the different terms or specifications they use can be confusing in many places. Here's a collation of relevant information to help you get a clear explanation of some of the terms and understand what they mean exactly in the context of pressure sensors.

Absolute Pressure - (PSIA): This type of sensor measures the equivalent of a pressure in an ideal vacuum. In other words, at sea level, when the pressure port is exposed to the atmosphere, it is measured (1 atmosphere = .

The output of the sensor will change with the change in atmospheric pressure.

Gauge Pressure- (psig): The sensor measures the pressure relative to the ambient pressure. The back of the sensing diaphragm is exposed to the atmosphere through some kind of vent, so any change in ambient pressure will affect both the exhaust port and the pressure port, so the output is stable.

Seal Pressure- (PSIS): This type of sensor measures the pressure relative to the atmospheric pressure of the seal. The back of its diaphragm is completely sealed, and it is sealed at about one atmosphere.

Differential: This sensor measures the pressure at one port and compares it to the pressure at the other port. Maximum Pressure: Maximum rated working pressure.

Pressure range: The algebraic difference between the maximum and minimum pressures, according to which the device can be calibrated.

Withstandable pressure: The pressure that can be applied to the sensing element of the sensor without causing a permanent change in the output characteristics. If this pressure is exceeded, the sensing element may be destroyed.

Damaged Pressure Rating: The maximum pressure applied to the sensor can lead to catastrophic failure. It must not exceed the damage pressure, which is several times the maximum pressure and the withstand pressure.

Linearity: Linearity refers to the maximum deviation from the linear relationship between the sensor output and the pressure within the operating pressure range. It is represented by the percentage that corresponds to the full output.

Repeatability: Continuous application at the same pressure produces the same output.

Hysteresis: The maximum difference in pressure from minimum to maximum and then from maximum to minimum output, the deviation is expressed as a percentage.

Typical accuracy – This is a combination of linearity, repeatability, and room temperature hysteresis.

Total Error – The maximum allowable error for each linearity, repeatability, and hysteresis at operating temperature.

Standard pressure: The pressure expressed by atmospheric pressure is the standard, and the pressure greater than the atmospheric pressure is called positive pressure; Less than atmospheric pressure is called negative pressure.

Absolute pressure: The amount of pressure expressed in absolute vacuum.

Relative Pressure: The amount of pressure for the comparison object (standard pressure).

Atmospheric pressure: Refers to the pressure at which it is atmospheric. The standard atmospheric pressure (1atm) is equivalent to the pressure of a column of mercury at a height of 760mm.

Vacuum; Refers to a state of pressure below atmospheric pressure. 1 torr = 1 760 barometric pressure (atm).

Detection pressure range: refers to the applicable pressure range of the sensor.

Withstandable pressure: The acceptable pressure that does not degrade its performance when restored to the detection pressure.

Round-trip accuracy (on off output): The pressure fluctuation value at the operating point obtained by removing the output and reversing the pressure value when the pressure is increased or decreased at a certain temperature (23°C).

Accuracy: At a certain temperature (23°C), when zero pressure and rated pressure are added, the value that deviates from the specified value of the output current (4mA, 20mA) is removed by the full-scale value. Units are expressed in %fs.

Linearity: The analog output varies linearly with the detected pressure, but deviates from the ideal straight line. The value that represents this deviation as a percentage for a full-scale value is called linearity.

Hysteresis (linear): Draw an ideal straight line between the output current (or voltage) value with zero voltage and rated voltage, and find the difference between the current (or voltage) value and the ideal current (or voltage) value as an error, and then find the error value when the pressure rises and falls. The maximum value of the absolute value of the above difference is the maximum value obtained by removing the current (or voltage) value of the full scale, and the resulting value is hysteresis.

Units are expressed in %fs.

Hysteresis (on off output: The value obtained by removing the difference between the pressure at the output point at the ON point and the pressure at the off point is the full-scale value of the pressure.

Non-corrosive gases: refers to substances (nitrogen, carbon dioxide, etc.) and inert gases (argon, neon, etc.) contained in the air.

There are many types of pressure sensors, and there are two commonly used types: piezoresistive pressure sensors and piezoelectric pressure sensors.

The working principle of piezoresistive pressure sensor is that when the varistor is pressurized, the resistance becomes higher and the pressure is repented, and the pressure can be detected by amplification by the amplifier and standard pressure calibration. The performance of a piezoresistive pressure sensor depends primarily on the varistor element (i.e., varistor), the amplification circuitry, and the calibration and aging processes in production.

Piezoresistive sensors use integrated circuit process technology to fabricate four equivalent thin-film resistors on a silicon wafer and form a bridge circuit. When not subjected to force, the bridge is in equilibrium and has no voltage output; When a force is applied, the bridge loses its balance and outputs a voltage proportional to the stress. Piezoresistive sensors work on the same principle as conventional semiconductor strain gauge sensors, which are based on the piezoresistive effect of semiconductor materials.

The piezoelectric pressure sensor principle is based on the piezoelectric effect. The piezoelectric effect is when some dielectrics are deformed by an external force in a certain direction, and their internal polarization will occur, and positive and negative opposite charges will appear on its two opposite surfaces at the same time. When the external force is removed, it will return to a state of non-positive charge, a phenomenon called positive piezoelectric effect.

When the direction of the force changes, the polarity of the charge also changes. Conversely, when an electric field is applied in the polarization direction of a dielectric, these dielectrics are also deformed, and when the electric field is removed, the deformation of the dielectric disappears, a phenomenon known as the inverse piezoelectric effect. There are many types and models of piezoelectric pressure sensors, which can be divided into diaphragm type and piston type according to the form of elastic sensing element and force mechanism reconstruction.

The diaphragm type is mainly composed of a body, a diaphragm and a piezoelectric element. The piezoelectric element is supported on the body, and the measured pressure is transmitted to the piezoelectric element by the diaphragm, and then the piezoelectric element outputs an electrical signal with a certain relationship with the measured pressure.

This sensor is characterized by its small size, good dynamic characteristics, high temperature resistance, etc. Modern measurement technology places increasing demands on the performance of sensors. Piezoelectric materials are best suited for the development of such pressure sensors.

Quartz is a very good piezoelectric material, and the piezoelectric effect is found on it. At present, the more effective method is to choose a quartz crystal cutting method suitable for high temperature conditions.

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