A New Digital Voltmeter Having High Rejection of Hum and Noise Substantial Rejection of Single-Ended Or Super- Imposed Noise Is Also Achieved

TECHNICAL INFORMATION FROM THE -hp- LABORATORIES Vol. 13, No. 6

PUBLISHED BY THE HEWLETT-PACKARD COMP 501 PAGE MILL ROAD, PAL0 ALTO, CALIFORNIA FEBRUARY, 1962 A New Digital Voltmeter Having High Rejection of Hum and Noise Substantial rejection of single-ended or super- imposed noise is also achieved. These characteristics are obtained through a new approach to digital voltmeter design-one in which the input and measuring circuitry is both floated and guarded and in which the measurement is SEE ALSO: Digital Recorder, p. 5 often accompany the made by an integrating technique rather than D-A Converter, p. 8 by techniques presently in use. The new voltmeter has five-digit resolution and measures up to *lo00 volts dc in five ranges with 300% over-ranging on the four lower ranges. The most sensitive range is an advance for digital voltmeters in that it has a full-scale value of only 100 millivolts. This high sensitivity results in a digital voltmeter that is much more suited to measuring the mil- livolt-level signals that are encountered in work involving thermo-couple and strain-gage transducers, a common field of use for digital voltmeters. For example, measurements made

DY-2401 A SIGNAL SOURCE DIGITAL VOLTMETER IGROUNDEDI SIGNAL SOURCE (GROUNDED)

IBRIOGE TRANSDUCER1 I I I I I DIGITAL VOLTMETER 2 I I I (UNGUAROED) I I LO I ! I I I I GROUND CHASSIS GROUND CHASSIS COMMON MODE COMMON MODE GROUND EQUIVALENT-vc GENERATOR t CHASSIS GROUND W EARTH (<'.' EARTH e n' (1 TO InV RMS) GROUND (1 TO IOV RMS) GROUND GROUND GROUND Fig. 1. Equivalent circuit showing how unguarded Fig. 2. Guarded measurement technique of Dymec voltmeter incurs errors from common-mode hum 2401A voltmeter acts to open ground loop to hum pickup. Current produced by hum pickup develops currents by reducing measuring-circuit-to-chassis ca- spurious input voltage across RL, but hum voltage pacitance C, to below 2.5 pf, giving common-mode across RR.is negligible due to high impedance of volt- rejection of 120 db at 60 cps. Effect of CI,CS is neg- meter. Large value typical of C, (0.1 pf) limits com- ligible, while voltage across RL is typically below mon-mode rejection to about 29 db with RL of 1 K. 10-7 volt. Average-reading nature of 2401 A further Shield offers negligible improvement because of low improves noise rejectiole. f value of Rc.

PRINTED IN U. S. A. COPYRIGHT 196.2 HEWLETT-PACKARD CO.

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__I_ __I Fig. 3. Dyinec 2401A the voltmeter. This effect is known Integrating Digital Volt- meter ha< fbfited aid as common-mode pickup, because guarded input to achieve one end of the equivalent hum gen- very high common-mode- noise rejection. Most sen- erator is common to both sides of sitive range of voltmeter the input signal pair. Common- is 0.1 volt full scale with resolution of 10 micro- mode pickup will cause a voltage to volts. Over-ranging of appear at the voltmeter input which 300~0is provided. can easily be as large as the sig- on the 100 mv range at a sampling operations have been made pro- nal itself, resulting in a completely period of only 0.1 second will have grammable by external contact clos- erroneous reading. A voltmeter with a resolution of 10 microvolts per ures, while all control lines and a conventional floating input can digit. This is ten times more sensi- electrical outputs are referred to reduce common-mode pickup to tive than has been available com- ground potential. Suitability of the some extent, but it is limited in its mercially. Three fixed sampling pe- instrument for systems use has been effectiveness by the capacitance be- riods of 0.01, 0.1, and 1.0 second further enhanced by avoiding elec- tween the measuring circuit and are provided to allow the optimum tromechanical devices in the meas- the instrument chassis. Current in- combination of speed and resolu- uring circuits, while in the pro- jection from the voltmeter power tion. gram circuits (and in the instrument supply is also a problem with this The increased sensitivity and res- as a whole) only one type of such type of instrument. Use of a heavy olution of the voltmeter are accom- device is used. This is the reliable ground bus or shield usually will panied by a commensurately-high reed-type relay which programs the not reduce common-mode pickup accuracy. As regards accuracy, in range attenuator. All circuitry in appreciably and may even increase fact, the overall performance of the the instrument is transistorized ex- it, due to magnetic pickup from the instrument is fully specified as to cept for four tubes used in the op- ground loop formed. stability, linearity, temperature ef- erational amplifier. The new voltmeter, however, in- fects, and calibrator performance. Electrical outputs representing corporates a shield or "guard" which This information enables the instru- the visual digital reading also have completely isolates the floated mea- 9 ment to be used with knowledge of been made available for operating surement circuit from the main the specific performance that will external digital recorders. chassis. In effect, the guard breaks be obtained under given conditions. THE NOISE PROBLEM the common-mode loop. By operat- The performance established for Hum pickup and other noise on ing the guard at the ac or dc po- the instrument is shown in the ac- the measured signal can reduce the companying table, but in short it reliability of reading of digital volt- ACCURACY SPECIFICATIONS can be stated that the instrument is meters of the commonly-used suc- FOR DYMEC 2401A VOLTMETER of the very high (0.01%) accuracy ACCURACY cessive approximation or ramp (Specifications hold for f10% line volt- class. types. Since these types of circuits age change.) To make the voltmeter conven- Stability (at constant temp.): measure the input signal at a spe- k .01% of full scale per day, 1/10/100/ ient for system work, all of its cific instant in time, they will be in lOOOv ranges. error by the magnitude of k .03% of full scale per day, 0.lv range. RESOLUTION AND RANGE VALUES Internal 2 lv calibration source: k .Ol% OF DYMEC 2401A DIGITAL VOLTMETER any noise present at the per month. instant of measurement. A Linearity (referred to straight line through zero and full scale calibration points): third type of digital volt- k .005% of full scale, zero to full scale. meter, the continuous-bal- linearity decreases to f .015% of reading at 200% of f.s. and to & .025% of ance type, is likely to"hunt" reading at 300% of f.s. for, but never reach, an an- Temperature Effects (+lO°C to +50"C) Note: Temperature effects can be coli- swer when noise signals are brated out before taking readings. t the time of meas- Scale factor: & .002% of reading/'C, O.l/lv ranges. The most frequent source 2 .0027% of reading/'C, 10/100/ lOOOv ranges. of noise is power line pick- Zero: up or hum which results k .002% of full scale/'C, 0.1~range. f .0008% of full scale/'C, l/lO/ from having two grounds in 100/100Ov ranges. the system-one at the sig- Internal Calibration Source: 2 .002%/"c. NOTE: Polarity Sensed and Indicated Automatically nal Source and the other at -2.

WWW.HPARCHIVE.COM a dc voltage to be measured is ap- C‘ plied to the integrator, the integra- 0 0 Fig. 4. Rejection charac- tor output voltage rises at a slope 2 I.’ 0 teristics Of Dymec 2401A and polarity that depend on the , voltmeter to noise applied 0 to voltmeter terminals. magnitude and polarity of the volt- 03/ Curves 1,2,? are for 1, age to be measured. ,’ 0 Oe19 and Oaol sam&ng The integrator output is con- / periods. Rejection characteristics have infinite- nected to two pulse-generating rejection cusps every I, channels, one triggered by a nega- and loo cYczes~ as / tive-going voltage, the other by a I shown.

measurements by means of an inte- --__--__---- - grating process. The amount of re- 1 1’ I C I jection that this process achieves for I I Y noise is substantial, although it 0 varies with the noise frequency and the amount of time used for integra- tion or averaging. Assuming that the peak noise does not exceed the Fig. 5. Circuit dc signal level, averaging results in arrangmmt of GUARD^ Dymec 2401A at least 20 db rejection at 55 cps Voltmeter. (0.1-second sample period) and, because the integral of a complete sine wave is zero, noise rejection COUNTER TGITSDATA SOLID-STATE =MAL DATA is essentially infinite at 60 cps and NIXIE’ DISPLAY TNlTs DATA other decade frequencies. The in- L _____-__--- _I strument’s rejection of superim- -AA -B- posed noise is shown in Fig. 4. For

WWW.HPARCHIVE.COM BRIEF SPECIFICATIONS Fig. 6. Dymec 2410A DYMEC 2401A AC/Ohms Converter is INTEGRATING DIGITAL VOLTMETER designed to be used with Dymec Digital Voltmeter -DC VOLTAGE MEASUREMENTS- to measure ac voltages INPUT Ronqes: 5 ronges from 0.lv to lOOOv full and resistances. scale. Selection by front panel switch or remote contact closure to ground. Polority sensed automatically. Overrongins: Overranging to 300% of full scale permissible, except on lOOOv range. multiple of 1 second, the counter DIGITAL RECORDING Attenuator switches automatically (in 3 ms) to lOOOv ranqe if overload exceeds 310%. registration needs only correct po- The voltmeter is arranged so that and is held there until reset by front panel pushbutton or remote contact closure to sitioning of the decimal point to it can directly drive the -hp- Model qround. Type: Floated and guarded signal pair. Sig- display a direct reading of the input 562A Digital Recorder to make nal pair and guard may be operated up to 500v above chassis around. voltage . automatic printed records of volt- input impedance: 1M on lv and higher The voltmeter display consists of age measurements on paper tape. ronges lOOK on 0.lv range. NOISE REJECTION a 5-digit Nixie@readout with indi- A number of other devices such as Overoll Common-Mode Rejection: Better than card punches, comparators, tape 140 db at oll frequencies, 160 db at dc. cation of decimal point, measure- ACCURACY ment units (e.g., volts or mv) and punches and other parallel- and (See text) serial-entry devices can be operated INTERNAL CALIBRATION SOURCE polarity. Polarity information is ob- t 1 volt internol stondard provided for self- colibrotion. Voltage reference is derived tained by sensing the active pulse using auxiliary Dymec equipment. from specially oged. temperature stabilized zener diode selected for drift of less than generator. Binary-coded-decimal re- 0.01% per month (see Accuracy specifico- FREQUENCY COUNTING tions above). May be compared with ex- cording outputs are provided for Since part of the voltmeter cir- ternol stondard and adiusted to within the displayed reading, range, mea- f .001%. cuit is in fact a frequency counter, TRANSIENT RESPONSE surement units and polarity. Response is instantoneous except for smoII this part has been made available loss of 2 digits if signol reverses polority. To prevent circulating ground for external use. This permits the -FREQUENCY MEASUREMENTS- currents from passing through the Range: 10 cps to 300 kc. instrument to be used to count fre- Gate Time: 0.01, 0.1, 1.0 second or manual signal source, as is possible in the quencies up to 300 kc with gate control (front panel switch or remote signal). circuit shown in Fig. 1, the guard Accurocy: f 1 count f time bose accurocy. times of 0.01, 0.1, or 1 second, or lnternol Time Eose: 2 0.01% stability, long circuit previously mentioned en- term. (Self-check control on front panel.) manually or remotely controlled. Input SensXvify: 0.1 to lOOv rms (front closes the analog-measuring portion panel sensitivity adjustment), or will occept Gates times are crystal-controlled to lv neqotive pulses, 2 ps min. width. of the voltmeter circuit. The shield- Impedonce: 1M shunted by 100 pf. an accuracy of approximately 0.01%. -GENERAL SPECIFICATIONS- ing is extensive and is designed so DISPLAY5-digit Nixie@ readout. Polarity, decimal that power frequency currents from AC/OHMS MEASUREMENTS point, measurement units and overload con- the internal power supply are not The new voltmeter can also be dition indicated outomaticolly. RECORDING OUTPUTS fed back to the measured source used to measure ac voltages to 750 Measurement units, function, numerical data and range represented by binary-coded deci- where they would appear as super- volts peak and resistances to 10 meg- mol output signals, suitable for operating -hp- 562A Digital Recorder or other externol imposed hum signals. The two ohms in conjunction with the devices, directly or via o Dymec coupler. pulse trains leave the guarded area Dymec 2410A AC/Ohms Converter FREQUENCY OUTPUT Internal 100 kc frequency standard is avail- through small shielded pulse trans- shown in Fig. 6. When the two in- able at rear BNC. formers. Outside the shield, all cir- struments are used together, the PULSE TRAIN OUTPUTS Three outputs are provided at individual cuitry functions with respect to readout including the units of mea- rear BNC connectors. EXTERNAL PROGRAMMING chassis ground, permitting all out- surement is given on the voltmeter. DY-2401A moy be completely programmed put and control lines to be refer- Units are also indicated on the Con- by external contact closures to ground. 3PERATING CONDITIONS enced to chassis ground with no verter. Measurements with the Con- Specifications apply for ambient operating !emperdure up to +50° C; relative humid- effect on the floating or guarding, verter are made with a floated and Ity up to 95% at 400 C. guarded circuit, and are fully pro- POWER REQUIRED INTERNAL CALIBRATOR 115/23Ov -C lo%, 50/60 cps, 150 watts grammable. approx. The voltmeter also includes a NEIGHT Net weight 48 Ibs.; shipping weight 70 Ibs. t 1-volt calibrator which has a sta- ACKNOWLEDGMENT opprox. bility of within f 0.01% per month. The Dy-2410A design group at 'RICE Model DY-2401A Integrating Digital Volt- The calibration procedure can be Dymec included R. M. Cook, Proj- meter, $3,950.00. All prices f.0.b. Polo Alto, Calif. carried out from the instrument's ect Engineer, R. Y.Moss, who per- Data subject to change without notice. front panel. The calibrator is formed counter and logic develop- DYMEC capable of being adjusted within ment, and R. E. Cooley, who per- A division of Hewlett-Packard Co. 0.001% when compared with a formed development of the con- 395 Page Mill Road Palo Alto, Calif. suitable external standard. verter section. -R. A. Andersen -4.

WWW.HPARCHIVE.COM /1 A VERSATILE DIGITAL RECORDER FOR BCD DATA The recorder itself is also fully transistorized. Additional features include electronic data storage and the ability to be arranged for dual input coup- ling. High accuracy analog records may be Fig. 2. New -hp- Model 562A Digital Recorder prints up to 3600 digits per made with potentiom- minute on paper tape. Optional analog eter or galvanometer circuitry occupies left portion of panel. type recorders by means of an optional tablish the dc level of these input Output feature swings as far as the recorder input Fig. 1. New -hp- Model 562A Digital Recovder (center) is concerned. The dc level of the operates from BCD codes to print digital data suck as that is completely in- BCD input can have peak values from counters on paper tape. Unit also has option of dependent of the print analog output to drive strip recorders. anywhere within a total range of mechanism. +150 volts with respect to chassis EVERAL years ago -hp- intro- Printing is accomplished with a duced two digital recorders mechanism similar to that of the -hp- ground. Fig. 3 illustrates this. which printed digital data from -hp- 560A and 561B Digital Recorders by By deriving the reference voltages counters and other digital equip- striking a print bar against pre-posi- for the input data from the driv- ment on paper tape at high speed. tioned print wheels. Each print ing equipment, compatibility with These recorders, one of whose first wheel represents an input column many types of equipment is assured uses was to record valuable frequen- and has associated with it a printed regardless of wide differences in out- cy information from Sputnik 11, circuit module containing circuitry put levels and swing amplitudes. could print up to 12 digits per line for data storage and selection of the Further, this arrangement greatly at speeds up to 5 lines per second for proper print character. For use with aids reliable data transfer from a total capacity of 3600 digits per digital frequency- and time-measur- source to recorder since any change minute. The recorders operated ing instruments, the printed circuit in environment or other conditions from electrical signals in the form modules are arranged for a 1-2-2-4 which might cause a change in code of staircasez and ten-line3 codes. BCD code with the “1” state positive amplitudes would have a similar A new recorder has now been de- with respect to the “0” state. Mod- effect on the reference voltages. So veloped which operates primarily ules for other codes and codes of long as the reference voltages are from the familiar four-line Binary the opposite polarity are available. separated by a voltage approximate- Coded Decimal system. The new re- Since each print wheel operates with ly equal to the code swing ampli- corder is a companion to its fore- its own module, different input tude, data will be properly entered runners and has the same character- codes may be used for separate to the recorder. istics with regard to speed, print ca- wheels. Furthermore, internal con- pacity, and reliability. In addition, nectors are provided for routing in- though, the new unit can also be put data to any of the column mod- I 1 directly operated from transistor- ules. The connectors are readily ac- ized as well as vacuum-tube equip- cessible so that any desired printing ment. The recorder can be used with format can be quickly established. counters, translators, computers, and FLEXIBLE INPUT many other digital systems. , One of the most useful features of SIGNAL TO BE - WITHIN t150V ‘“Sputnik’s Doppler Shift Measured and Recorded the new 562A Digital Recorder is TO GNO with -hp- Counter and Di ita1 Recorder,” Hew- lett-Packard Journal, Sup$. to Vol. 9, No. 1-2, the wide range of input conditions Sept.-Oct., 1957. ZAlan S. Bagley and Ed. A. Hilton “A Fast Digi- it can accept. Input voltage swings tal Recorder yjth Analog Outpu; for Automatic *’3 Data Plotting Hewlett-Packard Journal, Vol. 8, (between “0” and “1” states) may No. 7, March‘, 1957. Fig. 3. Diagram illustrating rmge of in- ‘Ed A. Hilton “A Fast, Auymatic Printer for be as small as 4 volts or as large as put voltage levels from which Recorder Digital Type ’Data Devices Hewlett-Packard Journal, Vol. 9, No. 9, Ma;. 1958. 75 volts. Two reference voltages es- can operate. -5.

WWW.HPARCHIVE.COM of reference voltages Fig. 5 shows the block diagram are required. This is for data storage, translation, and particularly useful print wheel positioning for a 1-2-2-4 where it is necessary binary decimal code. With no input to print from two data BCD voltages applied, the storage sources simultaneous- flip-flops will assume the condition ly (dual input coup- required to position the print wheels ling). Differences in to blank. With input supplied, the code weighting, po- storage transfer will be to the states larity, input swings dictated by the input data. and reference levels can be readily accom- PRINTING FROM modated. TWO SOURCES Fig. 4. Circuitry jor each printing column is located on At small additional cost, the re- separate plug-in circuit board. Various input codes and DATA STORAGE column arrangements are thus possible. corder can be provided with the in- Four-line data pre- put cabling needed for dual input The input impedance for this re- sented to the recorder is entered recording. In order to record from corder is exceptionally high. This into flip-flops which store the in- two sources, on a synchronized basis, permits direct recovery of data from formation to be printed until the the digital recorder must receive electronic equipment without the character wheels are properly po- two print commands, one from each need for buffer elements. Driving sitioned. This arrangement elimi- source. When the first print com- requirements are as little as 15 pa nates the need to inhibit the driving mand is received, it is stored and an into an input impedance of approxi- source during the mechanical scan inhibit signal is applied to the in- mately 270K. cycle. Once data is transferred to the strument furnishing the print command. When the second print com- INPUT CODE recorder flip-flops, the input equipment can be released to gather new mand is received, the print cycle For use with -hp- and Dymec equipment, the new recorder is pro- data. This will often increase the begins. Both driving instruments (“ vided to accept a 1-2-2-4 BCD code total amount of information that can are held off until the data storage with the “1” state positive with re- be recorded in a given time. For sys- cycle is complete, at which time spect to the “0” state. For other tem applications, the feature of in- both driving instruments are re- applications, different codes may be put storage will often permit simpli- leased. With this type of operation, obtained as required. In addition to fication of the control logic associ- the overall system is kept in syn- the above, column modules can be ated with data samplingand transfer. chronization, even though sampling furnished for 1-2-2-4 BCD code of

the opposite polarity, that is, with BRUSH the change from binary “0” to binary “1” represented by negative- going voltage. Also available as standard options will be column boards for 1-2-4-8 weighted BCD codes of either polarity. The specifications applying to input voltage swings, reference levels, input im- pedances and storage apply to all of these boards. Other four-line codes are available on special request. Col- umn modules may also be obtained for recording directly from ten-line data. STORAGE -’ Because each printed column has its own associated circuit modules, it is possible to intermix input codes 2 WEIGHT C INPUT within one printer, provided only that no more than two different sets Fig. 5. Basic circuit awangernent of -hp- 5624 Digital Recorder. -6-

WWW.HPARCHIVE.COM rates for the two driving instru- ACKNOWLEDGMENT who performed on the circuit de- 9 ments are determined independent- The design group for the Digital sign and Frank R. Berry who per- ly. In this way, data can be printed Recorder included the undersigned formed the mechanical design. simultaneously from two completely as group leader, Ronald C. Jensen -Ed. A. Hilton independent instruments, such as a counter and a digital voltmeter, or SPECIFICATIONS Paper Required: -hp- folded paper tape (15,000 prints per packet with single apocing), or two counters with different gate -hp- stondard 3-inch roll tape. MODEL S62A line Spocing: Zero, single or double. In "zero," times. DIGITAL RECORDER does not print, paper does not advonce. Power Requirements: 115 or 230 volts +lo%, Accuracy: Identical to input device used. 50 to 60 cps, approximately 130 watts. (4 ANALOG OUTPUT Printing Rote: 5 lines per second, maximum. prints per sec maximum at 50 cps; 50 cps Column Capacity: To 11 columns (12 available model with 5 prints per second available.) An analog output proportional to on special order). Dimensions: Print Wheels: 12 positions, numerals 0 through Cabinet Mount: 20% in. wide, 12% in. high, certain selected columns of data can 9, a minus sign, and o blank. Other symbols 18% in. deep. available. Rock Mount: 19 in. wide, 10Vz in. high, 16% add greatly to the usefulness and Input Requirements: in. deep. Data Input: Parallel entry 1224 BCD "1" Weight: flexibility of a digital recorder. The state +4 volts to +75 volts with respect Cabinet Mount: Net 35 Ibs. Shipping approx. to "0" state. Other codes and polarities 70 Ibs. new Model 562A accomplishes this available. Rack Mount: Net 30 Ibs. Shipping approx. 63 by making use of the function of in- Reference Voltages: Reference voltages re- Ibs. quired for both the "0" and "1" state. Price: Basic instrument with 1 I-column capac- put storage to derive a high accuracy Reference voltages not to exceed t150 ity; includes one BCD Input Cable and one volts to chassis. Input impedance approxi- BCD Input Connector Assembly for up to analog suitable for strip chart and mately 270 K ohms. nine column boards. Column boards, re- Hold-off Signals: Both polarities are available quired for operation, are not included. X-Y recorders of either the poten- simultoneously and are diode coupled; 10 -hp- Model 562A Digital Recorder (cabinet, ma maximum load. +15 v open circuit from basic unit), $1175.00. -hp- Model 562AR tiometer or galvanometer type. 1K source -5 v open circuit from 2.2K Digital Recorder (rock, basic unit), $1 150.00. source. NOTE: The Model 562A Recorder is The analog panel for this optional Print Command: + or - pulse, 6 to 40 volts available with several standord op- amplitude 20 /IS or greater in width, ac tions os to number of columns pro- feature is shown in the photograph coupled. vided, coding polarities, etc. Details on Analog Output (Option 4-T):(From 1224 "1" request. of Fig. 2. A switching arrangement state positive boards only.) Accuracy is & Prices f.0.b. factory. 0.5% of full scale or better. 100 mv for po- Data subiect to change without notice. permits the operator to select the tentiometer recorder; 0.5 megohm minimum load resistonce. 1 ma into 5000 ohms maxi- HEWLETT-PACKARD COMPANY consecutive columns of input data mum for galvanometer recorder. 1501 Page Mill Road to be recorded in analog form. Any Tronsfer Time: 2 ms. Palo Alto, Calif. 3 of the first 9 columns may be used as well as the right hand 2. The wide range zero and calibrate controls also on the analog panel make it possible to adapt the output to many different recorders and recording setups.

The analog conversion is derived Fig. 3. -hp- Model 580A Digital-to-Analog Converter. from the recorder's storage flip-flops and has the advantage of freeing the amp into 5000 ohms is available. Sam- sign for the digital-to-analog converter ple rates of 50 per second or higher are was performed by Ronald C. Jensen, with analog from dependence on the possible using this output. This is par- assistance in the production aspects from mechanism. Where only analog ticularly useful for recording from high Patrick A. Bohn. -Ed. A. Hilton speed digital systems. records are desired, the printing mechanism can be disabled. This INPUT REQUIREMENTS SPECIFICATIONS The Model 580A is arranged in its -hp- eliminates unnecessary use of the standard configuration to work with any MODEL 580A mechanism and permits data sam- of the new -hp- counters, and with all -hp- DIGITAL-TO-ANALOG CONVERTER and DY equipment with 4-line output Accuracy: 0.5% of full scole or better. pling rates far greater than the digi- kits. All of these counters are equipped Potentiometer Output: 100 mv full scale. Mini- mum load resistance: 47 kilohm. Calibrate tal recorder's maximum print rate. with 4-line BCD output in a 1-2-2-4 control. weighted code. Output kits are available Galvanometer Output: 0 to 1 ma into 5,000 The basic electronic circuitry used for other -hp- and Dymec counters and ohms or less. Zero and calibrate controls. Input Requirements: to develop the analog output from digital voltmeters that do not include a Data Input: Parallel entry 1-2-2-4 BCD. "1" 4-line output as a standard feature. The stote +4 volts to +75 volts with respect the 562A has been incorporated in 562A can also use the same 4-line kit. to "0" state. Reference Voltages: Reference voltages re- a separate instrument, the Model The wide range of input voltages pos- quired for both the "0" and "1" state. sible makes the 580A suitable for use in Reference voltages not to exceed k150 580A Digital-to-Analog Converter. many applications. The input swing on volts to chassis. Input impedonce approx. 270 kilohms. The performance characteristics and the 4-line 1-2-2-4 code may be anywhere Command Pulse: Positive or negotive pulse, 20 from 4 to 75 volts. As with the 562A, bsec or greater in width, 6 to 20 volts om- features of this instrument are reference voltages are required. They es- olitude. Transfer Time: 1 millisecond. treated in some detail in the article tablish the "0" and "1" state levels and Power: 115/230 volts, 50/1000 cps. may be anywhere within a range of + or Dimensions: 16% in. wide, 31/z in. hiqh, llV2 that follows. Functionally, the 580A -150 volts with respect to chassis. in. deep. Price: Model 580A: $525.00. is identical with the analog option ACKNOWLEDGMENT All prices f.0.b. factory. Data subject to change without notice. of the 562A. In addition to the undersigned, the de-

WWW.HPARCHIVE.COM discrete step then represents 0.1% of full A DIGITAL-TO-ANALOG CONVERTER scale and for practical purposes is an analog function. WITH HIGH OUTPUT RESOLUTION This output voltage is then attenuated and provides an output fcr potentiometer of measurement accuracy type recorders. It is also applied to an since only the least sig- amplifier whose output can be used to nificant digits are selected drive a 1 milliamp type galvanometer for analog conversion. TO recorder. derive the same informa- For maximum stability over a wide tion from a long strip of range of operating conditions, Model printed digital data would 580A incorporates a zener referenced be time-consuming and power supply for independence from line laborious. voltage changes, diode clamps to insure accurate voltage levels before mixing, DIGITAL-TO-ANALOG and compensation elements to maintain CONVERSION constant output over wide temperature As with the analog op- extremes. tion of the 562A, Model Because the source data is electronically 580A derives an analog stored and almost continuously presented voltage by making use of to the clamping and conversion networks, BCD data stored in input the analog outputs developed have good flip-flops. A switching ar- accuracy and resolution even with large, rangement connects any 3 frequent changes in input data. Accura- consecutive columns (or cies better than 0.5% of full scale may be the right hand 2) of the obtained. Fig. 1. New -hp- Nodel 580A D-A Converter (lotcler input-data to these stor- POTENTIOMETER center) enables digital data such as frequency cozinter age A Of 9 readinns to be recorded on either galvanometer or poten- input columns may be OUTPUT - accommodated from the tiometer type recorders. The potentiometer output is capable of driving source. delivering a voltage of up to 100 milli- For 4-line BCD input volts into a minimum load resistance of For many data recording applications, codes, the storage decade for each digital 47K ohms. Data sampling rates of over digital-to-analog conversion offers im- column consists of 4 transistor flip-flops. 10 lines per second may be handled with portant advantages. Strip chart records Analog conversion is accomplished by full specified accuracy and resolution. At of continuously changing data, for ex- first weighting the outputs from each of higher sampling rates, the output filter ample, are more readily analyzed for these flip-flops according to the code of that is used to prevent ringing in trans- trends and other change characteristics the data presented by the driving source. former input recorders limits the response than printed digital data. Examples in- In the block diagram of Fig. 2, the code of the 580A. clude such applications as telemetry, fuel is 1-2-2-4 and weighting resistors have flow measurements, frequency deviation values in this ratio. GALVANOMETER measurements, and oscillator stability and Each of the 3 storage decades then pro- OUTPUT inter-comparison tests. duces a staircase function with a level The analog voltage developed in the In addition, because changes in data proportional to the numerical value of its mixing networks is applied also to an can be handled at a faster rate with ana- stored BCD data. These staircases are in amplifier to provide a current source log recorders than with digital recorders, turn mixed in the ratio of 1, 10 and 100 suitable for driving galvanometer-strip digital-to-analog converters find impor- according to their decade value to pro- chart or X-Y recorders. Zero to 1 milli- tant use where high density plots of duce a single staircase function with a changing data are required. The use of an 1000 steps from zero to full scale. Each (concluded on p. 7) analog recorder substantially compresses the data over that possible with printed- tape digital records. Furthermore, for - measurements made under conditions of - CLAMP noise, the analog plot is useful for graphi- STORAGE - & DECADE - MIXING cal averaging to determine incremental MATRIX changes and line slopes. - Fig. 1 shows a typical setup for oscillator stability measurements. One of the new -hp- counters is used in conjunction UP TO 9 with the Model 580A Digital-to-Analog COL'S. OF Converter to make a direct plot of the DIGITAL DATi counter readings. For this test, the 3 least < significant digits have been selected for analog conversion. Since the frequency being measured is in the vicinity of 3 kc, a full scale change on the strip chart record amounts to a 3% change in the actual output frequency. The resolution chosen for the analog record in any measurement application will of course depend on the magnitude of the expected change. If the least significant two digits had been selected for this measurement, full scale resolution would be 0.3% of PRINT COMMAND ),- REjORDER b the oscillator output frequency. I I Y ,-A- With this recording arrangement, the RESET . DATA TRANSFER stability behavior of the oscillator during PULSE GEN PULSE GEN. the period of test may be readily determined. Both the magnitude and the character of the changes that occur are clearly presented. Furthermore, there is no loss Fig. 2. Circuit layout of -hp- Model 580A Digital-to-Analog Converter. -8-