ALABORATORY THERMOREGULATOR HOWARD M. WADDLE
AND
ROBERT E. IMHOFF*
Georgia Schwl ofTechnology, Atlanta, Georgia
A
THERMOREGULATOR capable of extensive use in the laboratory is herein described. The main advantages of this thermoregulator over the conventiond mercury type are that it is rugged, can be used over a wide range of temperature, and is capable of maintaining a constant temperature a t any of the temperatures. The problem of securing positive electrical contacts is reduced to a minimum. The thermoregulator can be used in any position. The author has used this thermoregulator to control the temperature of oil baths in distillations during which i t was necessary to vary the temperature of the oil bath from 50°C. to 225'C. a t 5" intervals. This thermoregulator uses the same basic principle as the de Khotinsky regulator1 which was later improved by P. E. Klopsteg and W. H.
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* Present address: 7519 Wade Park. Cleveland. Ohio. IDE
RHOTINSKY. A,, U . S. Pat. 1,375,780.
Stannard,%that is, the coiling and uncoiling of a bimetal helix with a decrease and increase in temperature. The main feature of distinction is its simplicity, ease of construction and low cost. The author feels that it will prove very satisfactory to the user where temperature control of * 0.3'C. is sufficient. The construction of the thermoregulator is apparent from the drawing. Plate B, upon which the contact base, G, and contact arm, H, are placed, rotates with respect to plate C. Plate C is attached to the brass pipe, E, by means of a set screw. Plates B, and C, are brass and can be cast in a foundry and subsequently turned down in a lathe. If this is done the cost of parts for the entire thermoregulator should not exceed -
1 KLOPSTEG, P. E. AND W . H. STANNARD. U . S. Pat. 1,629,710: 3. Oplical Soc. Am., 7, 179-86 (1923).
seventy-five cents. A convenient method of clamping the thermoregulator to laboratory stands is to thread an eighth-inch hole in the shoulder of plate C, opposite the set screw, and place therein a suitable threaded brass rod of from eight to ten inches in length. The bimetallic helix used gave a rotation of 1 for each degree rise on the Fahrenheit scale. This helix can be purchased from companies dealing in himetal.* The thermoregulator should be used in connection with a suitable relay that operates on a small current, yet is capable of making and breaking the heating load. Such relays can be purchased from local dealers or made from materials readily available.= Electrical contacts are made by attaching one flexible insulated cable to the fixed contact on plate B, the other contact being made a t any convenient place on the thermoregulator. The author uses the long rod which serves as a means of clamping the thermoregulator to the stands for this purpose. Since there is slight movement in the contact arm for a small rise in temperature, there is a tendency for arcing across the contact points, even though the sparking is reduced by means of suitable condensers. As a result of this arcinz the contacts
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* Helixes used in this work were furnished by the H. A. Wilson
Company, 105 Chestnut St., Newark, N. J., No. 1461 (F) Highflex 45.
BLACK,P. T., Science, 79, 322(1934).
become slightly burned; and hence greater pressure between contacts is necessary in order to make sufficient connection to operate the relay. This decreases the sensitivity of the regulator. The author uses a modified form of the Universal A.c.-D.C. Thermionic Relay described by Hershberg and H ~ n t r e s s . ~A 100-ohm resistance across the filament of the 71A tube is used to decrease the possibility of burning out the tube when the relay breaks a large load, thus causing an increased voltage. In this set-up only extremely minute current passes across the contacts. In order to set the thermoregulator to operate a t a definite temperature, the bath is brought up to that temperature, the iixed contact on the arm H is so adjusted that it just does not make contact with the contact on the moving contact arm J. This is done by rotating plate B with respect to plate C. Obviously, the range of the thermoregulator is not the range of the slot in plate B. The entire assembly, consisting of parts E, K, and J can be rotated with respect to the two plates. Thus a wide range is possible. In actual practice there is a slight elongation of the helix. This is of no consequence, for in extreme cases of elongation both plates B, and C, can be set closer to the helix K.
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H E ~ S ~ B EE.~ B. G .AND E. H. HUNTRESS. rsd. Eng. C h m . . Anal. Ed.. 5, 3 4 4 4 (1933).
