| 摘要 |
An apparatus for the determination of the water status of living and nonliving materials capable of measuring the vapor pressure of water in the material at thermodynamic equilibrium by matching a solution of known vapor pressure with that of the water in the material, detected by observing the thermocouple output comprising a plurality of spiral loop thermocouples, a recording means for observing the thermocouple output, switches for connecting the thermocouples to the recording means one at a time using latching relays, a pair of contacts for each relay, each contact comprised of layers of dissimilar metals so that the current flowing under a thermalvoltage at the thermocouple in proceeding through the contacts flows through a sequence of metals across the first contact and an exact reverse sequence of metals across the opposing contact. The thermocouple, switches, and relays are contained in thermal and electrical insulation that, together with the low thermal voltage associated with the relays, minimize thermal voltages in all parts of the circuit except the thermocouple. The thermocouple then is used to hold a solution of known vapor pressure that, when enclosed with the material of interest, can be changed until it matches the vapor pressure of water in the material, whereupon the output of the thermocouple becomes zero, identifying the vapor pressure and thus the chemical potential of water in the material.
|
