Thermocouple Placement Research Articles

Techniques for Thermocouple Placement and the Automation of Temperature Measurements in the Microenvironment of Kentucky Bluegrass1

AbstractA Kentucky bluegrass (Poa pratensis L.) sward is comprised of many closely spaced, minute plants forming a dense, low canopy. Measurements of soil and basal tiller temperatures require careful placement of many small sensors. The objectives of this research were to develop expedient methods for obtaining precise point measurements of tiller, thatch, and soil temperatures with thermocouples in the field. Measurements were made in ‘Touchdown’ Kentucky bluegrass mowed to 5 cm.Throughout the study, Chromel‐Alumel thermocouples were used. A 40‐channel, microprocessor‐based data acquisition system and a computer compatible nine‐track magnetic tape were used for uninterrupted data collection. Irradiance, measured approximately 1 km from the experimental site, and air temperature, sensed by an aspirated thermocouple located 1.5 m above the turf, were recorded simultaneous with sod temperature measurements.Thermocouples [20 AWG (0.81 mm)] placed horizontally and vertically, thermocouples [40 AWG (0.076 mm)] placed vertically, and thermocouples [40 AWG] fastened to 0.6 cm diameter wooden dowels were placed 2 cm below the thatch‐soil interface and compared for precision and placement expedience. Vertically placed fine‐gauged thermocouples (the most expedient means of installation) were as precise as the other methods. Although gauge did not influence precision in this test, in some situations (particularly vertical placement) the potential for error may exist due to heat flow along the wire.Two methods of thermocouple (40 AWG) placement into basal tillers were compared for expedience of placement and relative precision. In one method, thermocouples were threaded through the tiller base leaving the thermocouple bead inside the tiller with lead wire connection on opposite sides. The other method involved direct insertion into a hypodermic puncture in the tiller base. The inserted thermocouple method was found to be the most expedient, and no significant temperature differences were found between the methods. Tiller base temperatures measured in the field on a cloudy afternoon on 11 June 1979 ranged from 16.8 to 21.1 C, with a maximum difference of 0.6 C between the two methods (insignificant at the 0.05 level). The coefficients of variation for each method were not greater than 10.6. Temperatures measured during a clear afternoon on 12 June 1979 ranged from 23.1 to 31.5 C. At 1500 hours, the difference between the methods of placement was greatest (3.3 C) but was not significant at 0.05. The maximum coefficient of variation was 15.3 and 13.7 for the inserted and threaded thermocouples, respectively. Throughout the day, the threaded method had generally lower coefficients of variation.

Delayed drinking in response to electrical and thermal stimulation of the medial forebrain.

Water intake in response to electrical and thermal stimulation of the medial forebrain was studied in the goat. When the frontal wall of the third cerebral ventricle was included in a field of bipolar electrical stimulation a dipsogenic response was obtained after discontinuation of the stimulation. Release of antidiuretic hormone (ADH) was apparently also elicited. The water intake was roughtly proportional to the amount of current which had been applied during the stimulation period. Water consumption in response to stimulation attenuated the dipsogenic effect of subsequent stimulation, as did also pre-stimulatory hydration by stomach tube. A 2 degrees C elevation of the temperature of parts of the preoptic/anterior hypothalamic region for 40 min periods incuded cumulative drinking starting after 2.5 to 18 min. There were great interindividual differences in the amount of water consumed in response to the thermal stimulation, possibly due to variations in thermo-couple electrode placement. The dipsogenic effect of forebrain warming was inhibited by pre-hydration, and by lowering of the environmental temperature. The delayed thirst responses are discussed in relation to stimulus-bound drinking previously observed in the same and other species. It appears possible that the delayed drinking was a manifestation of artificially induced excitation of juxtaventricular "thirst" receptors.

Multiple Freezing Points as a Test for Viability of Plant Stems in the Determination of Frost Hardiness

A technique is presented for a simple, rapid, and reliable means of determining the viability of plant tissue subjected to freezing temperatures. Freezing curves of excised stems of Cornus stolonifera Michx., and several other genera were studied. Tissue temperature was recorded during freezing of plant stem sections. The heat of crystallization deflected the resultant freezing curves at points where tissue froze. Living stem sections of all genera studied revealed 2 freezing points, while dead tissue exhibited only 1. The influence of variables such as moisture content, sample size, thermocouple placement, and cooling rate on freezing curves was analyzed. Stem samples wrapped in moisture-proof film with a thermocouple inserted into the pith were frozen to a predetermined test temperature, thawed, and subjected to a second freezing cycle. The presence or absence of 2 freezing points in the second freezing cycle was used as a criterion for establishing viability. The results were immediately available and identical to results from regrowth tests which took about 20 days.

Thermocouple Placement in Chicken Carcasses

Abstract Considerable difficulty was encountered in replication of time required to cool during a study to establish accurate cooling curves of broiler carcasses in 32°F. water. Similar problems were reported by Nicholas and Havanesian (1960) who were working with freezing curves. They suggested a technic whereby the carcass was split, thermocouples were placed in exact positions, the flesh was sewn back together and the carcass was placed in a freezer bag prior to obtaining temperature changes. Since poultry carcasses are normally chilled without use of bags this method is not applicable. The purpose of this report is to outline the technic of thermocouple placement which was found most suitable in this laboratory and to compare it with other methods in general use. METHODS AND MATERIALS Thermocouples were mounted on a wooden probe as shown in Figure 1. Affixing the thermocouples to the probe allowed easier insertion and gave greater assurance of…