An Automatic Laboratory Flood-Control System The potential for property damage from flooding in the laboratory is a constant threat during ongoing operations which reTO A 1011 11 quire water coaling. We have developed an automatic flood conT O B IOR&I&MDI (ORE) T OE IORFI trol systemfor our Varian A-60 nmr Spectrometer which can be applied to any laboratory operation controlled by valves or -. . ... .. -. switches. The system utilizes an isolated, low-voltage (29 V, ac) sensing circuit employing a combined step-down transformer and relay costing less than $5. A schematic d i a ~ a mof the entire system is shown in the figure. (The unit-marked with a dashed line in the fignre-is available from Allied Electronics, part 1700-1900, ' $4.81, "ALCO," model FR 101 isolation relay, or Edmund Scientific, part t41,148 isolation relay, $4). The input is a 117 V, ae, 5 amp maximum, current applied at points C and D from a wall outlet. The current passes through s switch and a 5-A fuse (FU) to the ALCO isolation relay. The ALCO isolation relay pulls at 29 V, sc, 80 mA (contact points A-B). In our device this pulling current is considerably reduced to 7 mA by a Motorola MAC 10-2 solid state bidirectional thyristor ($1.35) as indicated on the diagram. Thus, the rating at the sensor leads (contact points E and F) is 29 V, ae, 7mA and is no safety threat. When the sensing circuit is closed, as by one drop of tap water, an output of 117 V, ae, and 5 A maximum may be applied along V and 2. This activates a Mallory (type SC 110) SONALERT Audible Signal Device (BU) ($8.75) and a Singer (CSFdM) delay timer ($23, adjustable up to 5 min). At the end of the delay time cycle, (three minutes for our system), the circuit load is applied along M and N. We use this output to close a solenoid valve (ASCO S210-B34, normally open, $46.00) shutting off the raw water supply to the instrument cooling unit and to open a 110 V, ac relay (Potter-Brumfield, PM17AY) shutting off the 220 V, ac power to the instrument and the 110 V, ac power to the pump which circulates the isolated distilled cooling water through the nmr magnet. The time delay cycle.insures that the instrument will not be shut down by accidental, small spills. The system can be deactivated during the delay cycle by turning off the switch or breaking the sensing circuit (at points E and F); in each case the delay timer is automatically reset. The'system must be activated continuously for the delay cycle time to shut the instrument down and must remain activated to keep the solenoid valve for the raw water supply closed. We have found the use of conducting tape (the same as used in window burglar alarm systems) for sensor leads to be best since the floor area for the potential flood thfeat can he cordonned. The sensing circuit may not be closed by distilled water. This can be remedied bv olacine a few eranules of salt dona the sensor leads.
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'Visiting Research Associate, Technology, Inc., 3821 Col. Glenn Hwy., Dayton, Ohio 45431 Julius G. Becsey Larry R. Froebel Aerospace Research Laboratories Wright-Patterson AFB, Ohio 45433
84 / Journaiof Chemical Education
