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A circuit to synchronise time marker, time base and stimulator
A C I R C U I T T O S Y N C H R O N I S E T I M E M A R K E R , T I M E BASE A N D S T I M U L A T O R MIC~tAZL G. SA~qDnS, M.B., M.Sc.
Department o~ Physiology and Medical Research, Uniq;ersity o~ Manitoba, Winnipeg, Manitoba, Canada (Received for publication: November 9, 1953) Customarily, when electronic stimulator and cathode ray tube systems are being used to study the response of a tissue to an electrical stimulus the time base and the stimulator are set off simultaneously by triggering pulses from some internal or external source. When making a photograph of the trace, the camera shutter is opened, an external trigger pulse made to set off the time base and stimulator and a
A
B
single response recorded on the film. A time mark may be added by switching over from the amplifier to a time marking source and a photograph of the time mark superimposed on the same piece of film. With a double beam cathode ray tube the time mark can be placed on one beam and the amplified response on the other. Although the system described is adequate in the majority of circumstances, when recording superimposed traces (Dawson 1947) the recorded responses will superimpose adequately because the time base and stimulator are triggered simultaneously, but the time mark will not superimpose because it holds no synchronisation with the time base. A tracing of the type seen in figure 1A will result. I n order to obtain a superimposed time trace it is necessary to synehronise the time marker, time base and stimulator. A circuit into which the trigger pulse feeds will effect this synehronisation when added between the time marker and the time base and stimulator circuits. Details of a circuit to do this are shown in figure 2A. The synehronising circuit is an Eeeles-Jordan trigger into one side of which are fed negative pulses from the time marker. These pulses keep the trigger pulled to one side. The triggering pulse is fed into the other grid and when it appears pulls the trigger over so that the plate of Y2 in figure 2A goes negative. The first pulse from the time marker coming after the triggering pulse pulls the plate of V2 positive again. A square wave appears across the plate load of V2, the leading negative going edge is set up by the triggering pulse and the lagging positive going by a time marking pulse. By feeding the square wave into a differentiating circuit a negative and a positive pulse are obtained, this positive pulse coincides with a time marking pulse and is used to A. Without synehronisation between the time marker and the time base and stimulator circuits. B. With synehronisation between all circuits. Note the lack of appearance of the initial time pulse and the stimulus artefact but the accurate superimposition of the time trace. C. In this ease the pulse to set off the time base precedes the first accentuated timing pulse, but the pulse to trigger the stimulator is this first timing pulse.
Fig. 1 Tracings of the time mark and the response to a stimulus taken on a double beam cathode ray oscilloscope. Ten superimposed traces. Time 1 and 10 msee.
[ 327 ]
328
MICHAEL
G. SAUNDERS
trigger the sweep circuit and stimulator. As the time marker, time base and stimulator are now all synchronised, with repetitive traces on a double beam tube, the time mark will superimpose as adequately as the recorded response. This is shown in figure lB. Whilst the synchronising circuit permits recording of a superimposed time mark, it still does not permit the trace to show at its very start a timing pip nor is a stimulus artefact demonstrable on the beam showing the recorded response. This is seen when figure 1B is compared with figure ]C. Both the initial timing pip and the stimulus occur either during the fly-back
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A. The Eccles-Jordan trigger used as a synehronising circuit. B. The basic circuit for the Miller integrator transitron. Circuit constants for 1 ke/see. with thyratron type time bases or during the initial blanked period with the integrator type generators. The loss of the stimulus artefact can be of some significance when very accurate time measurements are required to be made. By using a time marker that gives a trace made up of the frequency required and accentuated pulses at submultiples of this fre-
quency it is possible to produce a time trace which always starts with a visible accentuated pulse and with the stimulus artefact coinciding with this pulse. This is shown ill figure :lC. A time marking circuit found suitable to obtain the type of tracing seen in figure 1C consists of :~. 100 kc/sec, oscillator frequency divided in steps of 10 to 1 c/see. The dividing circuit for each step is tile Miller integrator transitron of Cocking (1946). The circuit is shown in figure 2B. From grid 1 may be taken a positive going square wave having an adjustable duration which can be made to last one tenth of the cycle. The accuracy of the duration is kept very high because of the synchronisation from the previous stage running at 10 times the frequency. With a square wave duration of 1 unit and a space of another 9, a division of 10 is achieved. The square wave is phase inverted and then by differentiating, first negative pulses are obtained and then one-tenth of the cycle later come the positive pulses. The negative pulses go to the synchronising circuit described above which is between the time marker ~mt the time base. The positive pulses go to a mixer tube to superimpose on the fundamental time marking frequency. The time base will always be trigger "~t one ~'ycle of the fundamental before the accentuated pulse appears on the time trace. In order to trigger the stimulator in synchronisation with the accentuated timing pulse these accentuating pulses are by-passed to another Eecles-Jordan trigger. One side of this trigger receives the triggering pulse which is also going to the time base and the other side receives the accentuating pulses. The stimulus is thus set off when the first accentuated timing pulse appears on the trace. SUMMARY A circuit is described which permits synehronisation between a time marker and the time base and stimulator circuits. A frequency dividing circuit is also described which triggers the time base just before the stimulator is triggered.
REFERENCES CocKzNo, W. T. Linear saw tooth oscillator. Wireless World, 1948, 5~: 176-178. DAwson, G. D. Cerebral responses to electrical stimulation of peripheral nerve in man. J. Neurol. Neurosurg. Psychiat., 1947, 10: 137-140.
Reference: SAv~v~.as, M. G. A circuit to synehronise time marker, time base and stimulator. EEG Clin. Neurophysiol., 1954, 6: 327-328.
Department o~ Physiology and Medical Research, Uniq;ersity o~ Manitoba, Winnipeg, Manitoba, Canada (Received for publication: November 9, 1953) Customarily, when electronic stimulator and cathode ray tube systems are being used to study the response of a tissue to an electrical stimulus the time base and the stimulator are set off simultaneously by triggering pulses from some internal or external source. When making a photograph of the trace, the camera shutter is opened, an external trigger pulse made to set off the time base and stimulator and a
A
B
single response recorded on the film. A time mark may be added by switching over from the amplifier to a time marking source and a photograph of the time mark superimposed on the same piece of film. With a double beam cathode ray tube the time mark can be placed on one beam and the amplified response on the other. Although the system described is adequate in the majority of circumstances, when recording superimposed traces (Dawson 1947) the recorded responses will superimpose adequately because the time base and stimulator are triggered simultaneously, but the time mark will not superimpose because it holds no synchronisation with the time base. A tracing of the type seen in figure 1A will result. I n order to obtain a superimposed time trace it is necessary to synehronise the time marker, time base and stimulator. A circuit into which the trigger pulse feeds will effect this synehronisation when added between the time marker and the time base and stimulator circuits. Details of a circuit to do this are shown in figure 2A. The synehronising circuit is an Eeeles-Jordan trigger into one side of which are fed negative pulses from the time marker. These pulses keep the trigger pulled to one side. The triggering pulse is fed into the other grid and when it appears pulls the trigger over so that the plate of Y2 in figure 2A goes negative. The first pulse from the time marker coming after the triggering pulse pulls the plate of V2 positive again. A square wave appears across the plate load of V2, the leading negative going edge is set up by the triggering pulse and the lagging positive going by a time marking pulse. By feeding the square wave into a differentiating circuit a negative and a positive pulse are obtained, this positive pulse coincides with a time marking pulse and is used to A. Without synehronisation between the time marker and the time base and stimulator circuits. B. With synehronisation between all circuits. Note the lack of appearance of the initial time pulse and the stimulus artefact but the accurate superimposition of the time trace. C. In this ease the pulse to set off the time base precedes the first accentuated timing pulse, but the pulse to trigger the stimulator is this first timing pulse.
Fig. 1 Tracings of the time mark and the response to a stimulus taken on a double beam cathode ray oscilloscope. Ten superimposed traces. Time 1 and 10 msee.
[ 327 ]
328
MICHAEL
G. SAUNDERS
trigger the sweep circuit and stimulator. As the time marker, time base and stimulator are now all synchronised, with repetitive traces on a double beam tube, the time mark will superimpose as adequately as the recorded response. This is shown in figure lB. Whilst the synchronising circuit permits recording of a superimposed time mark, it still does not permit the trace to show at its very start a timing pip nor is a stimulus artefact demonstrable on the beam showing the recorded response. This is seen when figure 1B is compared with figure ]C. Both the initial timing pip and the stimulus occur either during the fly-back
tOOk ~ {._ t v,.l ~ . /
Tri,Qer
p~~k~v~Time
I ~_.~ 47k
e, ,~, ,o-IJ ; ~ ' ~ ~ *""To,i
Iv,.
pips' ~ ' ~
~[
bo~s
Bt
to telllg~r time bose CI • C2= O.001
I
pfd. Fig.
[
I~ "
I "timemork-I kc.
2
A. The Eccles-Jordan trigger used as a synehronising circuit. B. The basic circuit for the Miller integrator transitron. Circuit constants for 1 ke/see. with thyratron type time bases or during the initial blanked period with the integrator type generators. The loss of the stimulus artefact can be of some significance when very accurate time measurements are required to be made. By using a time marker that gives a trace made up of the frequency required and accentuated pulses at submultiples of this fre-
quency it is possible to produce a time trace which always starts with a visible accentuated pulse and with the stimulus artefact coinciding with this pulse. This is shown ill figure :lC. A time marking circuit found suitable to obtain the type of tracing seen in figure 1C consists of :~. 100 kc/sec, oscillator frequency divided in steps of 10 to 1 c/see. The dividing circuit for each step is tile Miller integrator transitron of Cocking (1946). The circuit is shown in figure 2B. From grid 1 may be taken a positive going square wave having an adjustable duration which can be made to last one tenth of the cycle. The accuracy of the duration is kept very high because of the synchronisation from the previous stage running at 10 times the frequency. With a square wave duration of 1 unit and a space of another 9, a division of 10 is achieved. The square wave is phase inverted and then by differentiating, first negative pulses are obtained and then one-tenth of the cycle later come the positive pulses. The negative pulses go to the synchronising circuit described above which is between the time marker ~mt the time base. The positive pulses go to a mixer tube to superimpose on the fundamental time marking frequency. The time base will always be trigger "~t one ~'ycle of the fundamental before the accentuated pulse appears on the time trace. In order to trigger the stimulator in synchronisation with the accentuated timing pulse these accentuating pulses are by-passed to another Eecles-Jordan trigger. One side of this trigger receives the triggering pulse which is also going to the time base and the other side receives the accentuating pulses. The stimulus is thus set off when the first accentuated timing pulse appears on the trace. SUMMARY A circuit is described which permits synehronisation between a time marker and the time base and stimulator circuits. A frequency dividing circuit is also described which triggers the time base just before the stimulator is triggered.
REFERENCES CocKzNo, W. T. Linear saw tooth oscillator. Wireless World, 1948, 5~: 176-178. DAwson, G. D. Cerebral responses to electrical stimulation of peripheral nerve in man. J. Neurol. Neurosurg. Psychiat., 1947, 10: 137-140.
Reference: SAv~v~.as, M. G. A circuit to synehronise time marker, time base and stimulator. EEG Clin. Neurophysiol., 1954, 6: 327-328.