Absolute Transmitters vs. Minus Value Transmitters

Er, is this about pressure transmitters, or is it about something else?

absolute pressure transmitter

The absolute pressure transmitter measures relative to a hypothetical perfect vacuum.

The other measures relative to current barometric pressure.

Absolute transmitter measures the pressure above zero pressure including atmospheric pressure and Minus value is, it tends to measure vaccume.

An absolute pressure transmitter will measure 'real' pressure, which includes the international standard atmospheric pressure (i.e., one 'atmosphere' = 14.7 lb/in-squared, or something like 101.3 kPa), which is considered to be 'standard' air pressure at ocean level (at ocean coasts).

A minus-value (usually called a 'relative') pressure measures the pressure in relation to one standard atmosphere (so, degree of pressurization or vacuum relative to 'standard' outside pressure).

The difference between the two will always be the same:

P(absolute) = P(relative) + 14.7 lb/sq-in

The idea is similar to temperatures in Kelvin and Celsius. Kelvin measures 'absolute' temperature relative to the 'absolute zero' temperature, at which all atomic motion ceases. Celsius degrees are exactly the same as Kelvin ones, except that they measure temperature relative to the freezing point of water under standard conditions (at 0 C).

T(Kelvins) = T(Celsius) + 273.xx degrees

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