Understanding Pressure Sensor Specifications

General Pressure Descriptions

Absolute Pressure:  Pressure measured relative to a “perfect” vacuum.

 

Barometric Pressure Transducer:  An absolute pressure transducer measuring the local ambient (absolute) pressure

 

Differential Pressure: The pressure difference measured between two pressure sources.  When one source is a perfect vacuum, the pressure difference is called absolute pressure. When one source is the local ambient, the pressure is called gage pressure.

 

Gage Pressure: Pressure measured relative to ambient pressure.

 

Vacuum Range: The range of absolute pressure between a perfect vacuum (0 psi A) and one standard atmosphere (14.697 psi A)

 

Pressure Transducer:  A pressure sensor that translates the change in pressure to a high level voltage output or digital signal.

 

Pressure Transmitter:  A sub group of pressure transducers that translate the change in pressure to 4-20mA output.  The group of sensors typically require a sensing “load” resistor where the change in current is translated to a voltage.

 

Transducer Parameters

Burst Pressure:  The maximum pressure that can be applied to a sensor without rupture of either the sensing element or product housing.

 

Common Mode Pressure:  The maximum pressure that can be applied to both ports simultaneously of differential sensor.

 

Full Scale:  The algebraic difference between endpoints.  Where one endpoint is actual offset voltage and the other endpoint is the upper limit of the range.

 

Offset Voltage:  The output signal obtained when the reference pressure is applied.

 

Operating Pressure Range:  The specified range over a sensor’s intended measurement range.  Specified by the upper (Pmax) and lower (Pmin) limits.

 

Proof Pressure:  The maximum pressure that can be applied without changing the sensor performance or accuracy.

 

Reference Pressure:  The pressure used as a reference in measuring a sensor’s errors.

 

Reference Temperature:  The temperature used as reference in measuring a sensor’s thermal errors.​

 

Span or Full Scale Span (FSS):The arithmetic difference in the sensor output usually measured at the specified minimum and maximum operating pressures.

 

General Error Terms

 Auto Zero:  A technique for eliminating errors by sampling at one or more reference pressures, then correcting the output signal function.

 

Best Fit Straight Line (BFSL):The best straight line chosen such that the sensors response curve contains three points of equal maximum deviation.

 

Common Mode Error:  An error that is independent of the major input variable (pressure).For example, all offset errors are common mode errors.

 

Error Band:  The deviation of sensor response from it BFSL, define by lines on either side of its BFSL and including the maximum deviation measured for a given normal mode or common mode error.

 

 

Ideal Transfer Function:  The mathematical representation of the input (pressure) variable and determined output (voltage) of the sensor.

 

Normal Mode Error:  An error that is a function (proportional) of the major input variable (pressure).For example, all span errors are normal mode errors.

 

Temperature Coefficient: The error band resulting from maximum deviation of a sensors output parameter (offset, span) as temperature is varied from 25°C to any other temperature within the specified range.  Typically measured in V/°C and divided by sensitivity to express the magnitude of the error band in psi/°C.

 

Common Error Terms

Offset Calibration: The error band defined by the maximum error in calibrating the offset voltage.

 

Offset Error: The error band defined by the maximum deviation of the offset voltage from its specified valued.  This may include calibration, temperature coefficient repeatability and stability errors.

 

Offset Repeatability: The error band expressing the ability of a sensor to reproduce the offset voltage, measured at 25°C, after exposure to any other temperature and pressure within the specified range.

 

Offset Stability:  The error band expressing the ability of the sensor to maintain the offset voltage with constant pressure and temperature.

 

Offset Temperature Coefficient:  The error band defined by the maximum deviation in offset voltage as the temperature is varied from 25°C to any other temperature with the specified range.

 

Normal Error Terms

Hysteresis of Pressure:  The error band defined by the maximum deviation in output signal obtained when a specific pressure point is approached first with increasing pressure, then with decreasing pressure (vice versa) at a constant temperature.

 

Hysteresis of Temperature:  The error band defined by the maximum deviation in output signal obtained when a specific temperature point is approached first with increasing temperature, then with decreasing temperature (vice versa) at a constant pressure.

 

Linearity: The maximum deviation of measured output at constant temperature (25°C) from, best straight line determine by three points (offset pressure, half scale pressure, full scale pressure).

 

Sensitivity Calibration:  The error band defined by the maximum error in calibrating sensitivity.

 

Span Error:  The error band defined by the maximum deviation of the span voltage from its specified valued.  This may include sensitivity calibration, coefficient, linearity, hysteresis, repeatability and stability errors

 

Span Repeatability:  The error band expressing the ability of a sensor to reproduce the span voltage and temperature held constant.

 

Span Stability: The error band expressing the ability of the sensor to maintain the span voltage with constant pressure and temperature.

 

Span Temperature Coefficient:  The error band defined by the maximum deviation in offset voltage as the temperature is varied from 25°C to any other temperature with the specified range.

 

 

  

Overall Accuracy

 Total Error Band (TEB):  Maximum deviation from the Ideal Transfer Function expressed as a percentage of the %FSS over the compensated temperature range.  Includes calibration errors (Offset & Span), temperature errors (Offset & Span), pressure non-linearity, pressure and thermal hysteresis.

Understanding Pressure Sensor Specifications
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