A Miniature Stem Thermocouple Hygrometer

Abstract

An unprotected chromel-constantan thermocouple was mounted in a cavity (4 .times. 2 .times. 1 mm) with rounded corners in a chrome-plated brass block (10 .times. 6 .times. 4 mm). When installed against a soybean (Glycine max [L.] Merr.) xylem face, sealed with caulking gum and insulated with polyurethane foam and aluminum foil, even rapidly changing stem water potentials could be followed accurately. Temperature gradients were a problem.