Model 425A Delay Operating and Service Manual
Contents
1. Printed in U S A Model 425A Delay Operating and Service Manual ORTEC Part No 733190 Manual Revision F 1202 Advanced Measurement Technology Inc a k a ORTEC a subsidiary of AMETEK Inc WARRANTY ORTEC warrants that the items will be delivered free from defects in material or workmanship ORTEC makes no other warranties express or implied and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ORTEC s exclusive liability is limited to repairing or replacing at ORTEC s option items found by ORTEC to be defective in workmanship or materials within one year from the date of delivery ORTEC s liability on any claim of any kind including negligence loss or damages arising out of connected with or from the performance or breach thereof or from the manufacture sale delivery resale repair or use of any item or services covered by this agreement or purchase order shall in no case exceed the price allocable to the item or service furnished or any part thereof that gives rise to the claim In the event ORTEC fails to manufacture or deliver items called for in this agreement or purchase order ORTEC s exclusive liability and buyer s exclusive remedy shall be release of the buyer from the obligation to pay the purchase price In no event shall ORTEC be liable for special or consequential damages Quality Control Before being approved for shipment each ORTEC instrument2. commonly used for pulse work skin effect losses in the conductor are the predominant losses for frequency components below approximately 1000 MHz Skin effect losses result in high frequency attenuation which expressed in decibels increases as w An ideal step function pulse impressed on the line appears at the matched far end with the shape shown in Fig 1 The rise time from O to X percent can be expressed as multiples of T where To is the O to 50 rise time Table 1 presents some rise time conversion factors an example of the use of these factors is the following 10 to 90 rise time 29 0 0 17 To 28 83 To Fig T Step Function Response of Transmission Lines for Which Decibel Attenuation Varies as the Square Root of Frequency The time Ta is defined as the interval measured from the start of the output pulse to the point at which Eut 0 5 Ein In Fig 2 T is plotted against the delay length in Nanoseconds Table 1 Rise Time Conversion Factors Percent of Pulse Height Rise Time Factor 10 0 17 20 0 28 50 1 0 70 3 1 80 fa 90 29 0 95 110 0 15 30 60 120 a Cable Length ns E Fig 2 Calculated Variation of 7 with Cable Length for RG 5BA U For AG 58A4 U cable whose decibel attenuation varies as aa for frequencies between 100 MHz and 1000 MHz it is convenient to calculate To by To 4 0 X 10778 42 2 g 1 where A is the commonly tabulated attenuation at 1000 MHz e
3. arranty should follow the same procedure and ORTEC will provide a quotation Damage in Transit Shipments should be examined immediately upon receipt for evidence of external or concealed damage The carrier making delivery should be notified immediately of any such damage since the carrier is normally liable for damage in shipment Packing materials waybills and other such documentation should be preserved in order to establish claims After such notification to the carrier please notify ORTEC of the circumstances so that assistance can be provided in making damage claims and in providing replacement equipment if necessary Copyright 2002 Advanced Measurement Technology Inc All rights reserved ORTEC is a registered trademark of Advanced Measurement Technology Inc All other trademarks used herein are the property of their respective owners CONTENTS WARRANTY ruta ti Id a bla li SAFETY INSTRUCTIONS AND SYMBOL Sucre clio rt toas iv SAFETY WARNINGS AND CLEANING INSTRUCTIONS 0c cece eee eee eee tee eee eee V le DESOGRIPTION ct er eee A A AA ree ET 1 22 OFEGIFICATION Sissi ia 1 Je O O te a erates dere 1 A MAINTE NANG E sets cot Arte etc avedte ac eateet aia nandeneatautenae ace tetantalee et aa E E AAE 3 Oe Ed Ao siete eh aitedtie enedecing ciara tied abides ee caeh A 4 SAFETY INSTRUCTIONS AND SYMBOLS This manual contains up to three levels of safety instructions that must be observed in orde
4. ck Diagram of Apparatus Used in Production Testing Es discriminators and the coincidence circuit are adjusted to the middle of the edge of the decay curve i e 50 count rate The width of this edge is about 20 ps that is changing the adjustable air line by 20 ps can change the output counting rate from 100 to 0 When a delay is switched into the 425A branch the equivalent length of air line is introduced into the other branch lf the delay cable has the correct length the count rate will again be 50 if not the amount of required readjustment of the variable air line gives the error directly Both discriminators operate at 50 amplitude for this test The termination of the cable at any realizable discriminator input is not exactly 50 Q Commonly used circuits include the shunt capacity of a tunnel diode or the base of a fast transistor plus stray inductances and capacitances This slight deviation from perfect termination does not affect the delay definition appreciably because it is the same in both branches Finite test pulse rise time 1 ns also affects both branches equally and so it introduces only second order errors Also the air cables are not exactly lossless but the To is almost 2 orders of magnitude shorter than for RG 58A U so it can be neglected If a transmission line system were to introduce no reflections it would have to have a uniform impedance i i p throughout Since z LIC the ratio of i
5. must pass a stringent set of quality control tests designed to expose any flaws in materials or workmanship Permanent records of these tests are maintained for use in warranty repair and as a source of statistical information for design improvements Repair Service If it becomes necessary to return this instrument for repair it is essential that Customer Services be contacted in advance of its return so that a Return Authorization Number can be assigned to the unit Also ORTEC must be informed either in writing by telephone 865 482 4411 or by facsimile transmission 865 483 2133 of the nature of the fault of the instrument being returned and of the model serial and revision Rev on rear panel numbers Failure to do so may cause unnecessary delays in getting the unit repaired The ORTEC standard procedure requires that instruments returned for repair pass the same quality control tests that are used for new production instruments Instruments that are returned should be packed so that they will withstand normal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the designated ORTEC repair center The address label and the package should include the Return Authorization Number assigned Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the sender s expense and it will be the sender s responsibility to make claim with the shipper Instruments not in w
6. nductance to capacitance at each point would have to be a constant This cannot be achieved even for the cable itself and further deviations occur when cables must be interconnected and the pulses routed through switches At points of interconnection where excess inductance is encountered some small capacitance has been purposely added so that the ratio of L C averaged over the connection is correct Likewise the switches have been mounted so that averaged over the switch gives 50 Q even though from point to point there are deviations Thus reflections occur when the magnitude of the deviations and the distance over which they extend become appreciable when compared to the distance traversed by a pulse during its rise time ref 8 For most pulses used in data acquisition systems in the physics laboratory in which the rise time is equal to or greater than 1 ns the reflection introduced at each end of the each delay cable will be comparable in size to that incurred when two cables are connected together by BNC connectors and a BNC union The temperature coefficient of the delay of the cables used in the 425A is about 150 ppm C within 20 of room temperature 4 MAINTENANCE The assembly procedures peculiar to the 425A Delay are considered virtually irreversible therefore any warranty problems will be resolved by replacement of the module 5 BIBLIOGRAPHY 1 S Goldman Transformation Calculus and Electrical Tran
7. ners CAUTION To prevent moisture inside of the instrument during external cleaning use only enough liquid to dampen the cioth or applicator e Allow the instrument to dry completely before reconnecting it to the power source yi 1 ORTEC MODEL 425A DELAY 1 DESCRIPTION The 425A Delay is a single width NIM standard module that provides for signal delays in 1 ns steps from 1 7 to 64 7 ns This is the basic 1 7 ns instrument delay plus the switch selected additional delay Longer delays may be achieved by cascading several 425A modules Input and Output impedances are 500 The delays are accomplished by coaxial cables interconnected by strip line sections no power is required Delay accuracy and definition are discussed in Section 3 Theory 2 SPECIFICATIONS Input 50 impedance either polarity 1500 V maximum BNC connector Output 50 Q impedance delay is the sum of IN switches BNC connector Delay Lengths 1 2 4 8 16 and 32 ns may be added in any combination Minimum Delay 1 7 ns all switches OUT Delay Accuracy 100 picosecond or 1 for each delay section used whichever is greater Cable Type RG 58A U Power Required None Dimensions Standard single width module 1 35 in wide x 8 714 in high per TID 20893 Rev 3 THEORY Pulses transmitted through coaxial cables suffer both attenuation and distortion In the cable used in the 425A as in most cables
8. r to avoid personal injury and or damage to equipment or other property These are DANGER Indicates a hazard that could result in death or serious bodily harm if the safety instruction is not observed WARNING Indicates a hazard that could result in bodily harm if the safety instruction is not observed CAUTION Indicates a hazard that could result in property damage if the safety instruction is not observed Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product In addition the following symbol may appear on the product ATTENTION Refer to Manual DANGER High Voltage Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product SAFETY WARNINGS AND CLEANING INSTRUCTIONS DANGER Opening the cover of this instrument is likely to expose dangerous voltages Disconnect the instrument from all voltage sources while jt is being opened WARNING Using this instrument in a manner not specified by the manufacturer may impair the protection provided by the instrument Cleaning Instructions To clean the instrument exterior e Unplug the instrument from the ac power supply e Remove loose dust on the outside of the instrument with a lint free cloth e Remove remaining dirt with a lint free cloth dampened in a general purpose detergent and water solution Do not use abrasive clea
9. sients Prentice Hall New York 1945 2 P Behrend Theory of Pulse Technique for Coaxial Cables Z Angnew Physik 5 61 February 1953 3 R L Wigington and N S Nahman Transient Analysis of Coaxial Cables Considering Skin Effect Proc IRE 45 166 174 February 1957 4 Q Kerns F Kirsten and C Winningstad Pulse Response of Coaxial Cables revised by R Kirsten LRL Counting Note CC 2 1 Lawrence Radiation Laboratory University of California Berkeley 1959 5 W C Johnson Transmission Lines and Networks McGraw Hill New York 1950 6 H H Skilling Electric Transmission Lines McGraw Hill New York 1951 7 R Littauer Pulse Electronics McGraw Hill New York 1965 8 Hewlett Packard Company Time Domain Reflectometry Application Note 62
10. xplain the sense in which this definition is operational Two counters scintillation detect prompt coincidence gamma rays from a radioactive source The source is moved 120 cm away from one counter and 120 cm closer to the other If the cable delay from one counter is changed by 8ns by use of the 425A the two counters will be properly time realigned if the discriminators associated with each counter are operated at 50 amplitude In practice the experimenter cannot readily operate at 50 amplitude just to have the cable calibrations meaningful but using Eq 1 it can be seen that the timing difference between 0 and 50 amplitude is less than 20 ps for a 10 ns length of RG 58A U It is in this range of operation that discriminators are usualy used If the discriminator is to be used at a large percentage of full amplitude or if long delays are to be achieved at settings other than 50 corrections can be made by using Fig 1 or Table 1 as a reference For the above example a delay error of 0 26 ns would result if the discriminator were operated at the 90 level Figure 3 shows the block diagram of the apparatus used in testing the delay cables of the 425A A fast rising pulse is split into two branches one of which is the 425A Delay The other consists of sections of high quality rigid air lines with one adjustable section The delays between the See Section 5 Bibliography DISC RIMINA TOR Fig 3 Blo
11. xpressed in db 100 ft 20 to 24 for RG 58A U and Fis the length in nanoseconds Since the rise time is proportional to the square of the length if two equal lengths of a given type of cable are cascaded the rise time of the combination is four times the rise time of either length alone This is in contrast to the familiar case of amplifiers of Gaussian frequency response in which the rise time varies as the square root of the number of identical sections For this reason and also because the characteristic step function responses of cables and of Gaussian devices are so different the overall rise time of combinations cannot be calculated from the square root of the sum of squares of individual rise times either with cables alone or with cables combined with Gaussian elements Instead the overall response of a system with cables and other elements may be obtained graphically or with convolution integrals ref 3 using either step or impulse obtained from the derivative of the function plotted in Fig 1 function responses The above discussion makes it clear that the delay of a cable cannot be specified unless the point on the response function is specified For the 425A Delay an operational definition is chosen When the required delay has been selected by any one of the IN switches the 50 amplitude point will be delayed by an amount equal to the delay that would be effected by lossless delay line One example will serve to e
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