W. J. DeJarlais
Northern Regionol Research Loboratory, Peoria, Illinois 61604
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I siqde safety Devite for Unattended Laboratory Heating
In Figure 1 is shown an easily constructed, inexpensive device suitable for monitoring the overnight heating of reaction mixtures. All parts are readily obtained from electronic supply houses.
meter arm is reset. A varistor is connected across the power relay points to lengthen their life. A small aluminum sheet is bent for a chassis to mount the power relay socket inside the box. The wiring presents no problems (Fig. 2). Parts List'
Alarm meter relay, 0-50 mV. I>C movement, contacts rated 100 me. a t 115 \' ac. Allied Radio 65Z587 or equivalent. General Duroose enclosed relav. SPDT.' 35 ma 115 1' ac coil. Allied it%& 742665 or eqoi&ent. Varistor-540 1' ae. Allied Radio 60D 6694. Miscellaneous hardware: 5 X 4 X 3-in. gray hammertone minihox., oet,al socket,. fnse and holder. duolex mounded outlet. 6~~ 32 screws, lbck washers a n d &ts.'hind& .>. vosts,. rubb& grommets and feet, piece of aluminum bheet. ~~~~
Figure
1.
Heating monitor.
A thermocouple in an oil bath or in a heating mantle is connected to the binding posts on the front of the device. When a stable operating temperature is reached, the meter locking arm is moved to a point somewhat above the thermocouple voltage. If the operating temperature should go out of control and raise the thermocouple voltage to this point, a small magnet on the adjustable arm will lock the coil pointer to it and close the low current ac primary coil of a normally closed power relay in the device. When this relay is actuated, the electrical power to the heater, connected to the grounded outlets a t the rear of the device, is interrupted. Since the meter arm is locked in place by the magnet, the heat remains off until the 1 This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U S . Department of Agriculture. 2 Mention of firm names or trade products does not constitute endorsement by the U S . Department of Agriculture.
286
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Journal o f Chemicol Education
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rgoCla! 12OV
60 m Nena OUVI~K
necevtacle
Figure 2.
Wiring rchernotic.
