Document wgeJZbqBa3K4DpxQeKx032n16

Monsanto Chemical Company Anniston Method No. 14-36-4B ' SUBJECT: Dielectric Constant of Liquid Aroclor METHOD: Measured at 100C. and 1000 cycles Scope This method applies to mineral oils and oil substitute used for insu lating purposes; Apparatus Capacitance Bridge Cathode Ray Null Detector Oscillator Constant Temperature Oven Variable Air Condenser 1500 cc. Pyrex Beaker General Radio Co., Type 716-AM General Radio Co., *Type 707-A General Radio Co., Type 606-A Cenco-DeKhotinsky #95050 General Radio Co., Type 334-F Procedure Electrode and beaker must be cleaned as directed under "Cleaning Appa ratus for Dielectric Constant", end be at 100C. Heat Aroclor in the can to 105eC. Pour over electrode until plates and ceramic insulation are covered. Connect leads. Stir with thermometer outside oven until temperature reaches 101; place in oven which has been carefully adjusted to 100C. At the time sample is placed in oven its temperature should not have fallen below 90C. Connect leads to capacitance bridge, observing that the lead from insu lated side of condenser goes to insulated terminal on bridge. Balance bridge carefully according to direction under "Balancing Capacitance Bridge". Until Aroclor and oven temperatures have become identical the bridge balance will constantly shift. After oven temperature reaches 100C., maintain bridge balance until no pronounced shift is evident. Record reading of capacitance scale multiplied by multiplier setting. Dielectric Constant Capacitance in Aroclor at 100C. Capacitance in air at 100C. ' Balancing Capacitance Bridge Condensed procedure. Operator should read operating instruction for Null Detector for complete details. 1. Connect to power supply leads to oscillator and null detector. Ground the oscillator. ,2 Turn on oscillator by pushing 5000 ohm, 10 multiplier, 100 cycle ' frequency buttons. Adjust harmonic control until oscillation begins as shown by closing of sector in cathode ray tube. q 330877 STLCOPCB4077521 Page #2 Dielectric Constant of Liquid Aroclor - Teat 14-36-40 3. On null detector turn brilliance knob to extreme left, the focus knob to extreme right, gain control to extreme left, sweep amplitude st mid-scale position,-the sweep frequency switch on line side. 4. Turn on power switch, lighting pilot light. t 5. V.'ait fifteen seconds, turn brilliance knob to extreme right. 6. Adjust focus and brilliance knobs until sharp fine line. 7. Connect external terminals on detector to output terminals on oscillator. Switch,sweep frequency to external Bide. 8. Connect detector terminals of bridge to innut' terminals of detector, taking care that the black, wire (ground wire ) of the lead goes to grounded terminal cn both ends of lead. * 9. Set gain control at mid-scale and selectivity to extreme left. Turn sweep amplitude to extreme left, obtaining vertical line. :'Jith 10. With turning control knob-obtain the maximum length of this line, keeping it always under 1/4 inch with gain knob. 11. Set sweep amplitude to extreme left. 12. Set gain control to give vertical straight lino of about 3/8 inch,, 13. Balance bridge by adjusting power factor and capacitance dials until only a dot remains on the screen vhen the gain control is at extreme right. . *0 14c Set sweep amplitude beyond mid-point, and slightly displace the power-factor dial to obtain a tilted elipse. 15. Adjust phase control until this ellipse closes into a straight line inclined to the horizontal. 16. Bring power-factor dial back to balance position, which should restore the horizontal strai^it line. Displace this control the same amount in the opposite direction. This should again tilt the straight line but in the opposite direction. Adjust phase control until there is no tendency for this line to open up when it is swung 30 degrees from horizontal in both directions. . 17. Throughout these adjustments the other bridge control (the DSW 330878 STLCOPCB4077522 Page #3 .. Dielectric Constant of Licuid Aroclor - Test 14-36-48 capacitance Dial) must be in balance position. If the ellipse grad ually opens when the line is horizontal it may be brought back to the line again by making slight c'-anges in this control. If confusion results, balance both controls again as in (13) and repeat the suc ceeding adjustments. This is the position of bridge balance: An altexSticn of the power-factor control will tilt the line which does not open apprecia ble thru an angle of 30 to the horizontal both weys; an alteration of the capacitance dial opens the ellipse but does not change the inclination of the major axis. . The apparatus may be left in this balanced conditione turned off by switching off first the brilliance kn^b of the detector, then the power switch, then turning off the oscillator. For successive maasurements the controls are not changed, the apparatus left in adjustment. Then the following steps define the procedure: 1. Connect all leads as previously directed including that from null detector to bridge. 2. Turn on oscillator by pushing 100 cycle frequency button. So Turn on null detector, wait 15 seconds then turn on cathode ray tube. Turn-sweep amplitude to extreme left and adjust brilliance to obtain a fine vertical line on screen. 4. Bring: this line to a dot by adjustin'411 5th*e* *t*w*o bridge controls. Initial adjustment is facilitated by having "Gain" control to left. When final adjustment is obtained this knob must be at extreme right, 5, This dot remaining unchanged shews condition of brid~e balance. Cleaning Apparatus for Dielectric Constant The condenser is removed from the tested dielectric and allowed to drain while still in the oven at 100C. The condenser is then placed, while still hot, in a beaker of benzene under a well ventilated hood and allowed to cool. It is then thoroughly washed with powdered tri sodium phosphate and a 50-50 mixture of benzene and carbon tetrachloride followed by an acetone rinse. The operator should be very careful not to touch the metal plates of the condenser .after this point. The condenser is then rinsed thoroughly with tap water followed by distilled v?eter and dried on a clean paper in an oven at 120*C for at least one hour or until it is again used. nwb 3/1/48 ' DSW 330879 STLCOPCB4077523