US2762915A - Electronic decade scaler - Google Patents

Description

sept. 11, 1956 A. s. BAGLEY 2,762,915

ELECTRONIC DECADE SCALER Filed May 21, 1951 2 Sheets-Sheet 1 FIE J FIE E| United States Patent i' ELECTRONC DECADE SCALER Alan S. Bagley, Los Altos, Calif., assignor to Hewlett- Packard "Company, Palo Alto, Calif., a corporation of 'California This invention relates generally to decade scalers of the electronic type, such as are useful for the counting of electrical pulses.

In the past it has been common to connect a plurality of bistable multivibrators in cascade to form a chain for the counting of electrical pulses. A simple chain consists of four multivibrator scales in a binary manner by a factor of 16. Thus every sixteenth pulse applied to the first multivibrator results in la single output pulse from the fourth multivibrator of the series. In many laboratory and industrial applications it is desirable to provide for decimal rather than binary scaling. In the past this has been accomplished by a feedback circuit which connects from the last multivibrator of the series to the second and third multivibrators. With such an arrangement, on the eighth applied pulse the last multivibrator switches and provides a pulse which is fed back to the second and third multivibrators of the series to cause retriggering. After the tenth applied pulse all of the multivibrators are in the same condition as after the tenth pulse of the previous group. The chain has thus completed a counting cycle after ten applied pulses.

A decade sealer as described above is limited with respect to its counting speed. This is because the switching action in the various multivibrators does not occur instantaneously but requires a short interval of time in each instance. This causes a short delay before the next multivibrator in the chain can be triggered. At high pulse rates the delays are such that the switching time becomes an appreciable fraction of the multivibrator half cycle. As a result such decade scalers are not commonly considered or practical at rates higherthan about l mc.

In general it is an object of the present invention to provide a decade counter which does not possess the limitations of previous Sealers with respect to speed of count.

Another object of the invention is to provide a decade sealer having a novel feedback arrangement which makes possible relatively high speed operation.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure l is a diagrammatic view illustrating a prior art type of decade sealer.

Figure 2 illustrates curves to explain the operation of a simple sealer like Figure l but Without a feed back path.

Figure 3 illustrates a plurality of curves to explain the operation of Figure 1 with a feed back path.

Figure 4 illustrates a plurality of curves to explain the time delay in the sealer of Figure l.

Figure 5 is a diagrammatic view illustrating a sealer incorporating the present invention.

Figure 6 illustrates a plurality of curves to explain the operation of Figure 5.

i 2,752,9l5 Patented Sept. ll, 1956 The invention can be best understood after describing the conventional sealer illustrated diagrammatically in Figure 1. Such a sealer consists of four bistable multivibrators A, B, C and D which are connected in cascade. The pulses to be counted are applied to the input i0, and the pulses received by the output circuit 1l are differentiated and registered or recorded by suitable means not shown. A feedback circuit 12 connects the multivibrator D with the multivibrators B and C.

Without the feedback circuit 12 the chain of Figure l functions as a binary sealer, which counts by a factor of 16. ln other words, every sixteenth pulse applied t0 the multivibrator A results in a single output pulse from the multivibrator D. The curves of Figure 2 diagrammatically illustrate operation as a binary sealer. The irst curve in the group represents triggering pulses applied to the multivibrator A, while the second, third and fourth curves represent the outputs of the multivibrators A, B, C and D.

With the feedback circuit i2 the chain functions as a decade sealer as illustrated diagrammatically in Figure 3. It will be noted that because of the feedback of a resetting pulse from multivibrator D to the multivibrators B and C, the chain is reset after the tenth applied pulse.

The curves of Figure 4 illustrate the triggering action of the multivibrators, in conjunction with the feedback circuit described above. The dotted lines having arrows at their lower ends represent triggering pulses being repeated successively through the chain responsive to the eighth applied input pulse. The dotted lines having arrows at their upper ends represent pulses fed back from the multivibrator D to the multivibrators B and C. As previously stated, in such a system the switching action of each of the multivibrators does not occur instantaneously, but requires a short interval of time resulting in a short delay before the next multivibrator in the chain can be triggered. At higher pulse rates these delays are, such that the switching time becomes an appreciable fraction of the multivibrator half cycle. Thus the time interval required after the eighth applied pulse for the multivibrator B to be reset, is the sum of the delays in each multivibrator as the trigger is passed through the chain and back to the multivibrator B (i. e. ve separate delays). Instead of being retriggered immediately, the multivibrator B will not be retriggered at the time of the last (tenth) pulse of the cycle, as is indicated by the curves of Figure 4.

According to the present invention the resetting of the multivibrator chain is accomplished in such a manner as to substantially reduce the aceumulative delay.

As diagrammatically illustrated in Figure 5, l provide a chain of four bistable multivibrators A, B, C and D. Multivibrators A, B and C are connected together in cascade, and the multivibrator D has its output coupled to the multivibrators B and C by the feedback circuit M. Various types of multivibrators can be used. lt is preferable however to utilize a multivibrator having both plate and grid clamping as disclosed, for example, in Waveforms, by Chance, Hughes, MacNichol, Sayre & Williams, volume 19, Radiation Laboratory Series, pub-- lished 1949 by McGraw-Hill Book Co., Inc. (page 697).

Such a multivibrator circuit is particularly welladapted` for high speed counting operations. The plate clamping can be such that only a limited voltage swing (e. g. 20 volts for 6AH6 tubes) is obtained between conducting and nonconducting conditions of the multivibrator tubes. Such clamping is desirable because operation of the multivibrator is made substantially independent of normal variations in tube characteristics. This tends to make operation of the sealer relatively independent ofvarying characteristics in replacement tubes. Also plate clamping gives a more desirable rise' and decay characteristic and allows a favorable intermediate portion of the characteristic curve to be used. Clamping of the grids also tends to make operation of the individual multivibrators relatively immune to varying tube characteristics. In addition it tends to reduce the inherent time delay for a switching operation.

In conjunction with the multivibrators A, B, C and D, i provide a coincident circuit land a gate ,17. The gate 17 is shown connected by path 1 to the multivibrator A, and to the multivibrator D by path 2. The coincident circuit 16 is connected to the multivibrators E and C by the paths 3 and v4, and Vto the gate i7 by path 5. The gate 17 can be of the multigrid vacuum tube type, as for example Va multigrid electronic switch as disclosed in the previously mentioned Radiation `VLaboratory Series publication, page 379. The coincident circuit 1.6 can be of the multiple vtype as disclosed on page 381 of the same publication. The coincident circuit 16 is arranged whereby a positive pulse is applied `through path 5 to the gate 17 only when concurrent positive pulses are applied to the coincident circuit through paths 3 and 4, from the multivibrators B and C. Thus the gate 17 is conditioned to repeat a pulse applied from multivibrator A through path 1, when positive signal voltage is applied concurrently by way of paths 3 and 4, and under such conditions a pulse is applied by path 2 Vto the multivibrator D.

Operation of the sealer described above (Figure 5) is as follows: By reference to the curves of Figure 6 it will be evident that in the interval between the seventh and eighth applied pulses, multivibrators A, B and C are all in the same sense. Also this interval is the rst time at which the iirst three multivibrators are thus aligned. Under such conditions a positive voltage signal is applied to the coincident circuit through paths 3 and 4, to apply voltage through path 5 to the vacuum tube gate 1'7, whereby the gate is made receptive to pass a pulse from path 1 to path 2. On the eighth applied input pulse, the resulting negative transition of multivibrator A causes a sharp voltage pulse from the multivibrator to be passed through the gate and applied by path 2 to the multivibrator D. This serves to trigger the multivibrator D, before the gate 17 closes. As a result of triggering the multivibrator D, multivibrators B and C are triggered lby virtue of the feedback circuit 14. After being triggered by the ninth and tenth input pulses, all of the multivibrators revert to the same sense as after the tenth pulse of the previous group, thus completing a cycle. The dotted line having an arrow at its lower end between the iirst and second curves of Figure 6 represents application of the eighth triggering pulse to the first multivibrator A. The relatively long dotted line having an arrow at its lower end represents passage of a triggering pulse from the multivibrator A, through the gate 17, and to the multivibrator D. The two dotted lines having arrows at their upper ends represent application of feedback pulses from multivibrator D to multivibrators B and C.

By comparing the curves of Figure 6 with Figure 4 it will be evident that the scaler of Figure 5 greatly reduces over-all time delay, and thus permits counting at substantially higher speeds. This is because a pulse from the multivibrator A retriggers multivibrators C and B with only the inherent time delay in the multivibrators A and D.

In order to illustrate the elfectiveness of my invention, it can be stated by way of example that a decade sealer made as illustrated in Figure 1, with conventional bistable multivibrators which are not equipped with plate and grid clamping, will permit counting speeds up to about 1 mc. By the use of multivibrators having clamped plates and grids, this performance can be improved to provide counting speeds of the order of 5 mc. By use of the present invention, and with conventional types of multivibrators, the practical limit to counting speed can be increased to about 2 mc. By the use of multivibrators having clamped plates and grids, as previously described, and with the present invention, the counting rate can be extended to l() mc.

It will be evident that my invention can be incorporated in various types of laboratory-and industrial equipment, where it is necessary to carry out high speed counting operations. `For example, it can be used to advantage in connection with nuclear counting operations, frequency measurements, etc.

When incorporated in a commercial decade Scaler, it is desirable to employ a suitable input shaper for applying pulses to the-multivibrator A. It is'also desirable to take the output from the multivibrator C, although if desired the output can be taken from the multivibrator D.

In many instances it is desirable to couple the output to a second decade Scaler, which may be one of conventional design.

I claim:

l. lIn a decade sealer, three binary scaling devices connected in cascade to form a chain, a fourth binary scaling device, a gate, means serving to connect the gate between the rst and fourth of said scaling devices whereby when the .gate is open a triggering pulse is applied from the irst to the fourth device, a coincident circuit for controlling opening and closing of the said gate, said circuit being connected to receive controlling voltage from the second and third vscaling devices, whereby after the sixth of a series of triggering pulses is applied to the input of the first device, said second and third devices are conditioned to cause the coincident circuit to open the gate, and means for applying a triggering pulse from the fourth device to said second and third devices responsive to triggering of the fourth device by a pulse passed through said gateifrom the rst device.

2. In a decade sealer, three bistable multivibrators functioning as binary scaling devices and connected in cascade to form a chain, a fourth bistable multivibrator, a Afeedback circuit connected from the fourth of said multivibrators to both the second and third multivibrators of the chain, means forming a direct connection between the iirst and fourth multivibrators, a gate interposed in said c onnection and serving when open to permit application of a triggering pulse from -the first to the fourth multivibrator, a coincident circuit connected to control said gate, said circuit being connected tothe second and third multivibrators whereby after application of the sixth of a series of input pulses to the rst multivibrator, said second and third multivibrators cause application of two positive voltages to said coincident circuit to cause said coincident circuit to open the gate, opening of said gate causing the eighth applied input pulse of the series to apply a triggering pulse from the first multivibrator through said gate and to said fourth multivibrator, whereby said fourth multivibrator applies a triggering pulse to the second and third multivibrators.

References Cited in the file of this patent UNITED STATES PATENTS Bergfors Sept. 4, 1951 Phelps Feb. 5, 1952 OTHER REFERENCES

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