Automatic Event-Marking Device for Fraction Collectors Dennis R. Nelson, G . R. Anderson,’ and L. C. Snyder2 Metabolism and Radiation Research Laboratory, Agricultural Research Service, U S D A , Fargo, N . D. 58102
FRACTION COLLECTORS are used in many laboratory studies to make continuous collections of a column effluent, and the effluent is often monitored by a detection instrument with a flow-through cell and recorder. The data on the recorder and the fraction collector tubes must then be correlated by marking on the recorder trace the points at which the fraction collector changed tubes. This can be done manually with a hand-operated device such as the Beckman No. 92726 Auxiliary Pen Marker or automatically with a n L K B No. 3430 Event Marker or automatically with a fraction collector that is equipped with a n event marker output that can be used in conjunction with recorders equipped with a marker pen designed to be actuated by that output signal. However, these devices are either inconvenient t o use or are not readily interchangeable between different fraction collectors and detection instruments and recorders. This report describes the construction of a versatile eventmarking device that indicates o n a recorder trace the points a t which the fraction collector has changed tubes. I n addition to a fraction collector, the event marker can be used with any instrument that has a cyclic function from which a n electrical actuating signal can be obtained and with any single- or multi-channel recorder or with a recorder equipped with a n event-marking pen. APPARATUS
The event-marker described is for use with a 115 VAC input signal, but any input signal can be used; the only requirement is that the coil rating of relay K1 (Figure 1) must match the signal available from the fraction collector (a pin base was used for K1 for easy replacement if a n input other than 115 VAC is desired). The fraction collector output jack should be connected in parallel with a relay in the fraction collector which will operate each time the fraction collector changes tubes and that has a pulse of sufficient duration to close relay K1; this design will also provide for circuit protection by using fuses already in the fraction col1 2
Present address, Western Electric Co., Winston Salem, N. C. Present address, General Electric Co., Matoon, Ill.
Figure 1. Schematic diagram of event-marker, also showing connections to fraction collector, detection instrument, and recorder
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lector. (Many fraction collectors will already have a n output jack installed for event marking which will effect the same purpose.) The event-marker VOLTAGE output circuit is a voltage divider network (battery B1 and resistors R4, R5, and R6) that is activated when relay contact K I A is closed and a series circuit ( R l , R3, and R,) that is placed in parallel with the voltage divider network by the simultaneous closure of relay contact K1C. This series-parallel circuit places a voltage across R , (detection instrument output resistor) that is determined by the position of the R A N G E switch (Sl) and the setting of the AMPLITUDE control (R3) and that is added algebraically to the voltage already developed across R, by the detection instrument. The resultant voltage appears on a single-channel recorder as either a positive or negative spike superimposed on the data trace. (On a multichannel recorder, a second pen can be used to record the spike.) The only time the output impedance of the circuit need be considered is when relay K1 is closed; otherwise it is infinite (an open circuit). The maximum impedance of the event-marker is 87.7K ohms in the IO-mV position, and the minimum impedance is 33.9K ohms in the 100-mV position [calculated by using Thevinin’s equivalent circuit theory ( I ) ] , which will not have a significant loading effect on the detection instrument. The output circuit was designed to give a maximum spike height of 22% and a minimum,spike height of 10% of recorder input sensitivity when used with a Beckman D B spectrophotometer. The maximum can be increased by decreasing the value of R1, and the range of amplitude can be increased and the minimum spike height decreased by increasing the value for R3. The Beckman D B value for R, was 500 ohms; if a different instrument is used, the value of R, must be determined. If it is not 500 ohms, the values of R1 and R 3 must be changed. The resistor values should be calculated; however, there is a relationship that can be used asaguide(2): I f R , = 500ohms, t h e n R 1 = 3 3 K a n d R 3 = (1) H. V. Malmstadt, C. G. Enke, and E. C. Toren, “Electronics for Scientists,” W. A. Benjamin, Inc., New York, N. Y., 1962. (2) C. M. Close, “The Analysis of Linear Circuits,” Harcort, Brace and World, Inc., New York, N. Y., 1966.
Table I. Parts Lis@ Circuit Description Part number Quantity number Description Part number Quantity Eveready, E93 Battery, flashlight 1 R5 Resistor, 4.7 Kohm Ohmite 1 Plug, male, chassis Cinch Jones, P-3031 'IZW, 5% AB R6 Resistor, 470 ohm, Ohmite 1 52 Jacks, banana, red & H. H. Smith, type 2 'IZW, 5 z black 206 s1 Switch, rotary, 4Centralab, type 1 53 Jack, banana, green H. H. Smith, type 2 position 1465 206 s2 Switch, toggle, SPST Alco, MST205N 1 Klb Relay, 3PDT 1 Potter & BroomCartridge assembly for neon lamp Dialco, 507-87451 field, KRP-l4A, 504 120 VAC Llb Lamp, neon, red Dialco, 507-3835Minibox, 2-piece Bud, type CU1 1531-600 2105A P1 Socket, female, cable Cinch Jones, S-303Battery holder Keystone, type 173 1 CCT Socket, tube Amphenol, type 1 R1 Resistor, 33 Kohm, Ohmite 77MIP11 'hW, 5% Knob, range switch Kurz-Kasch, 293-31, 1 R2 Resistor, 1.5 Kohm, Ohmite Knob, amplitude Kurz-Kasch, 648-1L 1 v2w, 5% control R3 Potentiometer, 50 IRC, PQ-11-123 Dial plate Waldom, 410 1 Kohm, sealed R4 & R7b Resistor, 47 Kohm, Ohmite Plug, banana, red & H. H. Smith, type 4 black 236 1/2w, 5 % a Approximate cost for components was $25.00. If the fraction collector output is not 115 VAC, these components must be chosen to match existing output. KRP-14A is available in 6 to 110 VDC and 6 to 240 VAC. Dialco makes low voltage incandescent lamps for 6, 10, 14, and 28 VAC or VDC operation. Circuit number B1 J1
50K ohms; if R, = 1000 ohms, then R1 = 66K and R 3 = lOOK ohms; if R, = 2000 ohms, then R1 = 132K and R 3 = 200K ohms; if R, = 4000 ohms, then R1 = 264K a n d R 3 = 400Kohms. The C U R R E N T output circuit consists of the voltage divider network already described plus a series circuit (R2, R3, and R,) when relay contacts K1A and K 1 C are closed. R, is the internal resistance of a current recorder, and there is n o R, in the C U R R E N T function. The current-limiting resistor is R2 and should be a fixed value to protect the current recorder from an error in the setting of R3. The 100-mV range is also the 1-mA range for CURRENT. The other ranges 1 and 10 mV have currents that are too small, unless a current recorder of much less than 1 mA is available. The output jacks J3 provide a switching action (contact closure or opening, depending o n the wiring of K1) that can be used to activate a separate marker pen o n a recorder so equipped. The panel light L1 (neon lamp in series with R7, suitable for 115 VAC) gives a visual indication that the signal from the fraction collector is a t the event-marker.
DISCUSSION
The event-marker can be inexpensively built from the parts listed in Table I, which are standard values and readily obtainable. The list does not include the necessary wire, nuts, and bolts used for the assembly. Five of the automatic event-markers described have been used in our laboratory for 5 years in conjunction with fraction collectors and column effluent monitors (spectrophotometers, flow-through scintillation monitors, etc.) and have greatly facilitated determining which tubes contain the fractions of interest. The automatic event-marker has operated troublefree in the laboratory and in cold rooms, and the only maintenance required was the replacement of the 1.5-volt alkaline battery.
RECEIVED for review October 1, 1970. Accepted January 4, 1971. Mention of a proprietary product does not constitute endorsement of this product by the U . S. Department of Agriculture.
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