TERMIUM Plus^®

Record 1,  Textual support,  English

Record number: 1, Textual support number: 1 CONT

Thermocouple Psychrometry. A relatively modern technique for measuring water potential uses the flow of current through a small thin thermocouple (TC) to measure the water content of the vapor phase above a sample. Electrical current flows through a TC as a function of temperature, and temperature changes as water evaporates off the TC. The flux of water off the TC is determined by the amount of water in the vapor phase, which in turn, depends upon the water potential of the sample. Today, we will measure the water potential as well as the osmotic potential of some plant samples using the Decagon thermocouple psychrometer and nanovoltmeter. This device has nine sample chambers. We will fill three of the chambers with standard solutions to provide calibration of the TC, three with leaf samples, and three with crushed leaf samples (crushed to eliminate pressure potential P, leaving only osmotic potential as contributing to water potential). We will then let the samples equilibrate for 2 hours. We will need to calibrate the Decagon instrument to correct for the effect of temperature, pressure, and relative humidity on it's performance.  3, record 1, English, - thermocouple%20psychrometer

Record number: 1, Textual support number: 1 OBS

psychrometer. A device consisting of two thermometers, one of which is covered with a water saturated wick, used for determining relative humidity; for a given set of wet bulb and dry bulb temperature readings, relative humidity is read from a chart.  4, record 1, English, - thermocouple%20psychrometer

Record 1,  Textual support,  French

Record number: 1, Textual support number: 1 CONT

Actuellement les deux techniques les plus courantes de mesures du potentiel hydrique [...] sont : - le micropsychromètre. Le principe de la mesure est le suivant : si deux phases, une liquide ou solide, l'autre gazeuse, d'une même substance, ici l'eau, sont en équilibre, leurs potentiels hydriques sont les mêmes. Il est donc possible de mesurer le potentiel hydrique d'un tissu en déterminant le potentiel de la vapeur d'eau de l'air en équilibre avec lui dans des petites chambres de volume inférieur à un centimètre cube où l'échantillon étudié est enfermé pendant quelques heures. Le potentiel hydrique de l'air en mégapascal est alors égal à 1,064 T log U.  2, record 1, French, - micropsychrom%C3%A8tre

Record 1,  Textual support,  Spanish