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.