at i : "li- -757 UNITED STATES ATOMIC ENERGY COMMISSION Y-737 CONTINUOUSLY VARIABLE MAGNET POWER SUPPLY By W. D. Schultz March 8, 1951 Carbide and Carbon Chemicals Company Technical Information Service, Oak Ridge, Tennessee INSTRUMENTATION Reproduced direct from copy as submitted to this office. Work performed under Contract No. W-7Uo^-eng-26 PRINTED UN USA PRICE 5 CENTS AEC.Oak Ridge, Tenn. ,5-3l-51--570-W3700 ASSAY LABORATORY DEPARTMENT CONTINUOUSLY VARIABLE MAGNET POTVER SUPPLY INTRODUCTION ; The need for continuously scanning the mass spectra in the mass spectrometer has led to the development of a variable magnet power supply which will deliver from to 500 milliamperes to a magnet of 1100 ohms resistance,, The supply is a continuously variable, electronic, degenerative regulator which will regulate better than one part in 5000 throughout the range. Line voltage fluctuations of - 10 volts have no effect on the output of the supply. OPERATION : The power supply is actually two electronic degenerative regulators,, One of the circuits provides a constant voltage for the bias supply used in the main regulator,, The positive side of the bias regulator is necessarily at ground potential to supply a negative bias for V3 (See Figure 1). The grid of V]_ sees about one-half of any D*C<, voltage change on the output of the bias regulator. Since the voltage gain of the 6SJ7 is about 400(.l) when a 10 megohm plate load is used, a change of 1 millivolt in the output will cause a change of about 0<>2 volts on the grid of the 6T6 This high gain combined with the adjustment of the proper screen potential on Y^ produces a 300 volt output in which there is no detectable ripple nor any detectable variation in DoC levelo The adjustment of this screen potential is made with an oscilloscope connected across the bias supply to detect the point of minimum supply fluctuation.) The regulator proper consists of six 807's in parallel to pass the magnet currento These tubes were selected because of their low cost and high voltage handling capacity. The average plate dissipation for each 807 is 10 watts with a maximum of 20 watts at full supply current of 500 milliamperes. At zero current, 800 volts appear across the 807's,, The supply originally contained two 829' s as series regulators, but difficulty was experienced when high frequency oscillations tended to develop due to the common screen grid connection in each tube. Also, these oscilla- tions were probably due to the screen-to-cathode bypass capacitor built into the 829. A cost comparison also shows that six 807's cost less than one-half of the cost of two 829's. The 807 's are controlled by a 6SJ7 using a 10 megohm plate load*. The output as observed on an oscilloscope shows no ripple and less than one millivolt fluctuation in the D.C level,, The supply can have either positive or negative regulation depending upon the adjustment of Rga The adjustment of the supply is as follows s 1. Connect magnet or inductive dummy load and oscilloscope across the supply output, 2. With Ra set counter-clockwise, adjust R3 for zero current,, 3. Advance R* to full clockwise and adjust Rg to allow load current or 500 milliamperes. (Caution: Care must be used in setting R3 and Rg since there are two possible adjustments of these controls . The wrong adjustment will be indicated by instability in supply output and the positioning of the con- tact arm of R3 too near one end of the potentiometer.) 4. Return R^ to its counter-clockwise position and readjust R3 for zero current,, 5. Repeat steps 3 and 4 until the range of to 500 milliamperes is covered by the helipot control,, 6. Connect a voltmeter to the supply output and note the voltage at 500 milliamperes outputs 7. Break the connection between the supply and the load,, and note the voltage change on the output voltmeter . If any change is observed, correct for the change by rotating Rg a small amount. Continue this adjustment until a decrease of from 1 to 5 volts is noted in the 550 volt output when the load is placed on the supply. 8. The osoilloscope signal should show very little fluctuation at this point. Further minor adjustment of R2 and R3 may be necessary to obtain the best supply regulation. An alternate method for supply adjustment can also be followed, i.e.s 1. Set R4 midway between clockwise and counter-clockwise stops (5 turns). 2. Adjust R2 and R3 for best regulation as shown on an oscilloscope with an output current of between 220 to 270 milliamperes. 3. Adjust Rg and R7 for proper zero current position and full range of 500 milliamperes at maximum control position. (R4) The supply is constructed on two separate chassis as indicated by the separate schematic diagrams Figure 1 and Figure 2. Figure 2 is the diagram of the high -voltage rectifier supply which has a D.C. output of 800 volts at 500 milliamperes. This high voltage is chosen to give the best possible regulation in the range in which the regulator is intended for use. This range is around a load current of 400 milli- amperes. At this current, a voltage of 350 volts appears across the 807 regulators, and by experiment, the best regulation occurs between 200 and 500 milliamperes of load current. It was thought that it might be advisable to include a switch for cutting out 3 or more of the 807*s for better regulation in the low current range. This idea was discarded because of the possibility of overload should the supply be run at high currents with the 807's out of the circuit. Regulation at low currents is more than adequate for stable operations of the mass spectrometer. It is intended that this regulator be used with a motor driven poten- tiometer (R4)o The mechanism for driving the potentiometer was not completed at the time of the writing of this report. The heart of the drive will be a Brown 2-phase balancing motor to give variable speed and reversibility. The author wishes to thank Mr. E. S. Lewis and Mr. D. L. Glovier for their assistance in the construction and testing of this equipment. BIBLIOGRAPHY ; (1) G. E. Hamilton and T. Maiman: Voltage Regulated Power Supplies, Part II, Communications , December, 1945, P. 701 OOOO0® ♦-W ME '001 MOZ'XSI MOZ'MSI fAAr-rA/V-» MOl'MOZ MOI '* OC „iodn3H„ nvna ■A 0£ g^y 6 S10VJ.NOD/ ONIIMOHS A/v /y "-VNA/V •# £y «orxse -AAA/—" MSZ A *S MOI'XOI A OCZ'O* ^AA — YA — / Wv- j » Ml '*00l A *OS MI'MOOI I MM 'MZ'XOS UU *90£d UiQJ UU Isl M > A A 6 A 4: > > « IO 10 <0 10 Ub LqJ LqJ tH09d HO0NVJ.S 7f eojizi NOS -i-tf\J>-K> ^ TO MAGNET CONTROL PANEL 115 VAC -oro — o\) THOR- TO NO. 6 D ARSON T2I F02 mm Vsmsisu "THORDARSON" T483«0 CSCCC-4A-I98I5 fcWuWffiriTuin 300 MA. 866 866 FIGURE 2. Continuously Voriable MAGNET SUPPLY TRANSFORMER PANEL END OF DOCUMENT UNIVERSITY OF FLORIDA 3 1262 08909 0293