CFSensor Pressure Sensors: Innovation and Reliability for Industrial Applications
Thanks to advanced manufacturing technology, dedicated R&D teams, a scientific approach to production management, and rigorous packaging and testing standards, CFSensor is able to produce high-quality pressure sensors at exceptionally competitive prices.
Absolute, gauge, and differential pressure
Fundamentally, sensors measure the pressure difference, P, between the upper side (P1) and the lower side (P2) of a diaphragm, expressed as P = P1 - P2.
Absolute pressure sensor: Here, P = P1 - P2, but since P2 is sealed at zero pressure (vacuum), the result is simply P = P1.
Gauge (relative) pressure sensor: This measures P = P1 - PA, where PA represents the ambient atmospheric pressure.
Depending on the sensor type, P1 can be either higher or lower than the atmospheric pressure.
Differential pressure sensor: This measures the difference between two pressures, P = P1 - P2.
Again, depending on the sensor type, P1 may be higher or lower than P2.
Depending on the type and pressure range, the sensors are designed to withstand 1,5 to 2 times the rated pressure without damage or parameter drift.
Some types also specify a pressure level that will not yet cause mechanical failure (burst pressure), typically around three times the rated pressure. However, once a sensor is exposed to this pressure, its parameters will no longer comply with the datasheet specifications.
How a piezoresistive MEMS pressure sensor works
Piezoresistivity
Electrical resistivity, ρ, quantifies how much a material opposes the flow of electric current.
The resistance, R, of a body with length ℓ, constant cross-section A, and resistivity ρ is:
When a resistor made of p-type silicon is subjected to stress, the resistance change caused by the piezoresistive effect (ρ) is significantly larger than any change caused by geometry (ℓ, A). Because of this, we can neglect geometric changes and express the resistance shift as:
Here πL and πT are the longitudinal and transverse piezoresistive coefficients, while σL and σT represent the stress on the piezoresistors.
The simplest practical sensor
At its simplest, a practical pressure sensor consists of four piezoresistors integrated into a flexible silicon diaphragm. The diaphragm is an n-type silicon wafer, typically tens of micrometres (µm) thick.
P-type piezoresistors are implanted onto it using boron ions, roughly a few micrometres thick. Pressure bends the diaphragm, creating high tensile stress zones near the edges, exactly where the resistors are placed.
These four resistors form a Wheatstone bridge. The two longitudinal resistors (R1, R3) increase resistance under tension, while the transverse ones (R2, R4) decrease resistance.
Nodes Vs+ (1) and GND (3) are connected to a known input voltage Vin or current source Iin. Output voltage Vout appears between nodes Vo+ (2) and Vo- (4).
Uncompensated sensors
These sensor units contain only the four piezoresistors on a flexible silicon diaphragm, forming a Wheatstone bridge, connected directly to the package pins.
They can be powered using constant voltage or constant current, but for the XGZP160, XGPZ166, XGPZ167, XGPZ168, XGPZ183, XGPZ185, and XGPZ190 series, a constant current source is a better approach, as it gives you better temperature coefficients TCO (offset) and TCS (span).
The XGZP170 and XGZP182 series, however, are designed for constant voltage.
Depending on the sensor and pressure, you'll see a nominal output (FSS – Full Scale Span) between 30 and 120 mV at 5 V or 1 mA.
| Important: Manufacturing tolerances mean that the output voltage is not zero at zero pressure (offset), and that sensors with identical specifications will still show slightly different output levels at the same pressure. Both offset and FSS are also temperature-dependent. While offset can be compensated relatively easily, variations in FSS and temperature effects cannot. If your application demands higher accuracy, a sensor with offset and span compensation, or a fully calibrated sensor, is the better choice. |
Example: The XGZP160040S gauge pressure sensor (40 kPa), powered by a constant current source of 1 mA, has an offset of ±10 mV and an output voltage at nominal pressure of 55…75 mV (65 mV ±15,4%).
The TCO and TCS are ±0,02 %FS/°C (typ.) and ±0,05 %FS/°C (max.) over a temperature range of 0 to 60 °C.
Sensors with offset and span compensation
These sensor units take the uncompensated core and add laser-trimmed resistors to compensate for the offset and span spread. They also come with a thermistor to handle temperature compensation.
Example: The XGZP195050SG gauge pressure sensor (50 kPa, gauge, 10 V), has an offset of ±1 mV and an output voltage at nominal pressure of 38,5…41,5 mV, or 40 mV ±3,8%.
The TCO and TCS (Temperature Coefficient of Offset and Span) are ±20 µV/°C (max.), corresponding to ±(0,048…0,052) %FS/°C over the temperature range of 0 to 60 °C. These are impressive figures, especially considering that voltage-powered sensors typically exhibit TCO and TCS values of around ±0,2 %FS/°C.
Calibrated sensors with digital or voltage output
Calibrated sensors take things a step further. They use a dedicated ASIC to compensate for offset and span errors, non-linearity, repeatability, pressure hysteresis and temperature effects. This allows the manufacturer to specify a single, meaningful parameter: total accuracy.
Sensors by CFSensor offer either a digital I²C interface or a voltage output. Most devices achieve a total accuracy of ±2% or ±2,5% of Full Scale Span (FSS) over a temperature range of 0 to 60 °C. Most sensors operate from a 5 V supply, but customised versions for 3,3 V or 3 V systems are also available.
The XGZP6891D series supports a wide supply range from 2,5 to 5,5 V.
| If you need higher accuracy (for example ±1% FSS), operation from 3,3 V or 3 V, or a customised output voltage range, just let us know. We’ll discuss your requirements directly with the manufacturer and make sure to find the right solution. |
A wide range of CFSensor pressure sensors is available on our website. The most commonly used types are in stock and ready for immediate shipment, while additional variants can be supplied on request. We're also here to help you select the right solution for the application.
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