Thermocouples potentiometer with

The Boyd and Harkins reference might be considered the first careful calorimetric work taking into account the special problems of immersional calorimetry it was also the first such work in which surface areas could be assessed (the B.E.T. method) as a necessary auxiliary for putting values on a imit area basis temperatiue changes were measured with a 36-junction thermocouple and a White double potentiometer with a sensitive galvanometer. 

Thermocouple gauges work on a similar principle but have a thermocouple as sensor connected to a heated platinum filament. The e.m.f. of the thermocouple is measured with a galvanometer or potentiometer. Such gauges have a normal working range from 10 to 10" Torr, but otherwise have characteristics similar to Pirani gauges. 

The substrate is mounted about 25 mm. away from the vapor source in a copper frame which holds it in place, backed by an externally heated copper block. In this manner the lower face of the substrate is exposed to the vapor beam and maintained at the desired temperature by heating it at its upper face. The temperature is regulated within about 1 % by a proportionating potentiometer controller. The substrate consists of a square plate of an ionic salt with sides approximately 5 mm. long and 1 mm. thick. A freshly cleaved face of the salt crystal is exposed just prior to a run. A thermocouple in contact with the lower face of the support indicates the film temperature. 

Since the specimens were supported from the balance by a 2-mil Nichrome wire, a direct measurement of the specimen temperature was impractical. Instead, the temperature of the inner ceramic tube between the heater wires and under a surrounding ceramic coating at a point opposite the specimen in the tube was taken as the sample temperature. Previous observations for our system showed that the tube and the specimen had a temperature difference of less than 1°C. when the system was heated at a rate of 3° to 4°C. per minute at temperatures of 800° to 950"C. The temperature was measured, using a platinum and platinum-10 % rhodium thermocouple with a White potentiometer. 

Insulated Joule-Thomson cell similar to that of Fig. 2 (suitable stainless steel frits can be obtained from chromatographic parts suppliers, e.g., Upchurch Scientific part C-414) metal or nylon tees, crosses, and reducers (available from Swagelok and other manufacturers) -in. Teflon rod type T insulated copper-Constantan thermocouples with 0.010-in.-diameter wires voltmeter with 0.1-jU.V resolution (e.g., Keithley 196), null voltmeter (e.g., Hewlett Packard 419A or Keithley 155), or sensitive potentiometer (e.g., Keithley K-3). Cylinders of CO2, N2, and He with regulators and control valves 50 ft of l-in. copper coil, -in. and 1-in. polyethylene tubing 0- to 10-bar Bourdon gauge 25°C water bath. 

Procedure. The furnace should be turned on the day before measurements are to be made so that it will achieve a steady temperature. Set the power supply to a predetermined voltage appropriate for the desired reaction temperature. The heating current should be measured with a series ammeter and recorded periodically. At the start of the experiment, place the reference thermocouple junction in a Dewar flask filled with ice and distilled water (see Chapter XVII) and connect the thermoconple to a potentiometer or digital voltmeter (see Chapter XVI). Measure the thermocouple emf and check to see if the furnace is at the proper... 

Thermocouples are constructed by joining two dissimilar metals. Such a junction will produce a potential which is proportional to the temperature. These couples are almost always used in pairs and connected to oppose each other s potential. One is kept at a fixed temperature (usually the melting point of ice), and the other is used as the temperature-sensing element. The potential between the two couples, measured with a potentiometer, will be proportional to the temperature difference between the reference temperature and the observed temperature. 

The Leeds Northruj) transformation-point indicator is a semiautomatic recorder giving a continuous curve of temperature temperature difference. The complete apparatus includes the recorder, two wall-type double-suspension galvanometers, furnace, rheostat and thermocouples. The recorder is the potentiometer type with a drum chart. The potentiometer slide wire is mounted on the same shaft as the... 

For these studies it was desirable to maintain a constant temperature of about 22 C (room temperature). Since the amine-epoxy polymerization is an exothermic process, the syringes must have sufficient surface area to dissipate the evolved heat rapidly. Tests with Leeds and Northrup Potentiometer and a small alumel-chromel thermocouple, inserted into the center of the syringe, showed a maximum temperature rise of less than 2 C during the entire reaction time. This was sufficiently small to assume that isothermal conditions were maintained. 

The reactor furnace (Figure 2) consisted of an Alonized (alonizing in this case prevents oxidation of the copper) copper pipe, and each reactor was placed in one of the seven equidistant slots provided around the pipe. Three electrical heaters were stacked in the hollow center of the pipe, and the temperature of each heater was controlled separately with a Barber-Colman Model 20 solid-state controller. Besides placing thermocouples in the copper pipe, one thermocouple was embedded in the catalyst in each reactor to record its temperature with the help of a potentiometer and a multi-point recorder. The operation of several reactors in parallel enabled us to evaluate simultaneously the performance of identical catalysts with different amounts of sulfur. 

Fig. 4.10. Scheme of experimental setup for studying TSC in movable joints Ml-P-M2 (1) lever load unit (2) aluminum cylinder with a polymer coat on the face (3) thermocouple (4) polymer coating (5) copper disc (6) potentiometer (7) galvanometer (8) copper needle... 

The emf of the bulk liquid thermocouple was measured with a 10,000 juv L N White double potentiometer, using a dc chopper amplifier and strip chart recorder to record the potentiometer unbalance continuously on a chart annotated so that it could be correlated with the chart recording the test-piece resistance. 

Since the cell temperature is measured with a copper-constantan thermocouple, the absolute accuracy is dependent on the accuracy of the thermocouple calibration. This calibration was done in place with reference to the triple point and boiling point of nitrogen and the triple point of argon. The resultant accuracy was estimated to be 0.1°K, while resolution of the potentiometer (L N type K-3) was 0.03 K. In regard to pressure, the accuracy was 0.025 or 0.1 psi, depending on whether a mercury manometer or Bourdon-type gauge was being used. 

The temperature distribution within the cryostat was measured with six 20-gauge copper-constantan thermocouples located throughout the cryostat, these thermocouples being referenced to the resistance thermometer. Thermocouple emf s were measured with an L N Type K-3 potentiometer in conjunction with a Model 9834 electronic dc null detector. Inasmuch as these differential thermocouples generate small emf s, their accuracy is limited by the potentiometer, this accuracy being 0.02°C in this investigation. During operation the temperature distribution in the bath liquid was within 0.1°C of the resistance thermometer. 

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