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technical terms

GLOSSARY OF TECHNICAL TERMS

Find hereafter a useful glossary of technical terms on the subject of pressure measurement.

 

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  • absolute pressure

    In rare cases it can prove necessary to measure the - physical - pressure in absolute terms (e.g. in closed systems). The sensors used in such cases must be specially encapsulated, however.

     

  • conversion factor

    1 mbar = 100 Pa
    1 bar = 14,5 PSI
    1 PSI = 68,95 mbar 

     

  • characteristic curve

    The relationship between measured value and the output value is described by the characteristic curve. This is ideally a straight line.

     

  • deviation of characteristic curve

    hysteresis
    The hysteresis is the difference of the output value for a fixed measured value under increasing or decreasing pressure.

    deviation from the linear

    The devation from the linear is the amount of deviation from the characteristic curve of a reference line.

    reproducibility
    The reproducibility defines the largest deviation from the characteristic curve of a reference line.

    temperature error
    The temperature error shows the maximum deviation of the characteristic curve from the ideal case - for measurements taken at different temperatures - within the compensated sector. The temperature error is normally given as a value applicable to the entire compensated sector and not per 10K or 1K. Deviation of the characteristic curve in accordance with IEC 60770. This value defines the maximum overall error in accordance with IEC 60770, composed of non-linearity, hysteresis and reproducibility in keeping with the boundary setting, i.e. the deviation of the initial and final values from the straight line. As compared with the initial vaule setting or BFSL (best fit straight line), this definition gives the largest characteristic-curve deviation, but it is the easiest method for the user to understand. When accuracy details are given in data sheets, therefore, the error definition must also be specified.

  • initial value (offset)

    The lowest measured value to which the measuring device has been collimated. e.g.: 20 mA

  • differential pressure

    Differential pressure is the difference between two pressures to be measured.

    Mit Differenzdruck bezeichnet man den Unterschied zwischen zwei zu messenden Drücken.

  • response time

    The response time describes (act. to DIN EN 61298 and DIN EN 60770) the period between the start of the step response time and the time for the output to reach and remain within 1% of output span of its steady value. The step corresponding to 80% of output signal, giving an output change from 10% to 90%, then another from 90% to 10%.

    Synonymical (in the standards DIN EN 61298 and DIN EN 60770) it can be used the definitions response time and settling period.

     

  • final value (full scale)

    The highest measured value to which the measuring device has been collimated. e.g.: 20 mA

  • accuracy

    The actual permissible extent of deviation from the ideal characteristic curve is specified in terms of accuracy.

    "FS" = Full Scale = final value (e.g. 20 mA)
    "FSO" = Full Scale Output = span (e.g. 16 mA)

    The accuracy specifications are always given as a percentage of the range of measurement (FSO).

  • hydrostatic level measurement

    The pressure exerted at a particular depth of a given fluid above the position in question. For water, which has a density of 1 g/cm³, the pressure increases by around 100 mbar per metre of water depth. By calibratingon the basis of the density applicable for the fluid in question, the output signal of a hydrostatic level probe can be adjusted to the depth of fluid to be measured.

     

  • relative pressure

    Normally the pressure is measured relative to the prevailing air pressure, i.e. the air pressure corresponds to 0 bar. For pressures greater than the air pressure, positive values (overpressure) are obtained. For pressures smaller than the air pressure, negative values (negative pressure) are obtained.

     

  • types of sensors

    Piezoresistive silicon sensors
    non-encapsulated for gases and dilute, non-aggressive fluids with stainless steel membrane for standard industrial applications
    stainless steel thin film sensors
    for hydraulics applications and high dynamic pressure load

    thick film ceramic sensors
    for aggressice environments 

    capacitive ceramic sensors 
    for aggressive environments and very small ranges of measurements

  • range / full scale output (FSO)

    The algebraic difference between final value and initial value e.g.: 20mA-4mA=16mA

     

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