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An analog and digital readout system for the circulating memory
NUCLEAR
INSTRUMENTS
A N D M E T H O D S 42 (1966) I54-I56; © N O R T H - H O L L A N D
PUBLISHING
CO.
AN ANALOG AND DIGITAL READOUT SYSTEM FOR T H E CIRCULATING M E M O R Y V. BONAt~IC
Institute "Ruder Bo'~kovi~", Zagreb, Yougoslavia Received 10 January 1966 An analog and digital readout system for the circulating memory of a pulse-height analyzer is described and analyzed. Simultaneously one obtains here the spectrum display by the analog system and precise knowledge of the number of pulses in each channel by the digital system. The spectrum display is recorded
1. Introduction Logic circuits used in circulating memory pulseheight analyzers are usually simpler than the circuits of their readout systems1-3). The advantages of the described readout system are the simplicity of its logic and improved reliability. In this analog and digital system the readout is performed by subtracting unity by each memory cycle from the content of a selected channel. Thus the content of the selected channel is changed into a pulse train which is counted by a decimal counter. Simultaneously with the pulse train the capacitor is being charged by a constant current. When the channel content becomes equal to zero it is registered in decimal notation on the decimal counter and represented in analog form by the voltage on the capacitor. The two systems can display the content simultaneously as well as separately. In the digital system the channel content is represented in decimal notation and printed by a mechanical printer. In the analog system the content is changed into the analog voltage which deflects the pen of the recorder. Pulses performing the subtraction of unity from the channel content change the content of the observed channel only. After the readout of the content of a selected channel the transfer to the next channel is ensured by reliable identification of this transfer. Fig. 1
r
K
A
I
t. 2°
2~o - . . . .
ko ~ tZR,~1
I ,.11 o
~
l
[
I
r
I ~kn+l
C ....J" .....
Fig. 1. Time sequence diagram.
1
C J
by a pen recorder, whereas the channel content is printed by the digital system in decimal notation on paper tape. The advantages of the described readout system are the simplicity of its logic and reliability in work.
I
I
ok i
Fig. 2. Diagram of the pulse generator.
shows thecirculating memory cycle which starts by the reference pulse r. The channel content is recorded in binary notation .and the pulses representing it are synchronized with respect to the reference pulse. The channel K o is always empty and therefore the readout of its content is not performed. The logic of the readout system provides conditions for such an operation of the system. After the readout of the last channel the memory content is no longer changed.
2. Description and analysis The block diagram of a digital and analog system for the circulating memory readout is shown in fig. 3. The system consists of a pulse generator GI, which generates pulses for the subtraction of unity from the content of a selected channel, a logic for the digital and analog system, a pen recorder W for recording the spectrum display in analog form. A printing unit is used for printing the content in decimal form. The printing unit contains two counters and a mechanical printer. The ordinal number of the channel is recorded on the first counter, whilst the channel content is recorded on the second counter. The printer prints the content in decimal form from the counters onto paper tape. The pulse generator GI is shown in fig. 2. A detailed analysis of its operation is given in 4). After the pulse 154
AN
_~-7.- r
1
-
I°
L
ANALOG
AND
I
DIGITAL
READOUT
155
SYSTEM
of the observed channel becomes shorter than the delay time tz, the pulse (ok) passes through the anticoincidence A K and through the coincidence K and triggers the univibrator UV. During its quasistable state (Tu) the capacitor Ca is discharged by the constant current ii and therefore the duration of the pulse (o) is shortened by the amount:
I
t b = A2t o = (in/ik)B--(1/ik)C ; B : (Ck/Ca)Tm;
C = (Ck/Ca)Tni i.
(2)
The condition for the automatic holding on the desired channel is determined by the inequality: Tk -- (TB,ml,+ tb) > tz > ta + TBomln. i
IMEMORY
Fig. 3. Diagram of the analog and digital read out system. analysis the switch P is closed and the readout process is started. The capacitor Ca is charged by the current i~. During the memory dead time m the voltages on the capacitors Ca and Ck become equal through the linear coincidence LK, C a > Ck. The capacitor Ck is discharged by the current i k. The pulse width (o) at the output of the discriminator D is proportional to the voltage on the capacitor Ck and by each memory cycle it is increased by the amount: ta = Alto = (in/ik)A;
A = (Ck/Ca)T m.
(1)
The quantities ofeq. (1) are given in figs. 1 and 2. When the trailing edge of the pulse (o) appears after the channel pulse k o the readout of the content of the first channel starts. To perform the readout of a channel, the trailing edge of the pulse (o) should appear before the channel pulse of the channel to be read out and after the preceding channel pulse. By the trailing edge of the pulse (o) the binary B is switched to the state 1. The pulse k switches back the binary B to the state zero and the pulse (ok) is generated. The pulse (ok) passes through the coincidence Kz, subtracts unity from the channel content and adds unity to the counter content for channels in the printing unit. The trailing edge of the pulse (o) is held by automatic control through the pulse generator GI, between two channel pulses until the selected channel is read out. When the interval between the trailing edge of the pulse (o) and the channel pulse
(3)
The quantities TBom~n and TBlmi. ensure the triggering of the binary B to occur. The other quantities are given in fig. 1. After the readout of the selected channel the channel content becomes equal to zero. The circuit for the identification of zero in the arithmetic circuit of the analyzer produces the pulse CE. The binary B 1 is switched to the state 1, unity is added to the counter for recording the ordinal number of the channel, and the automatic control for holding the pulse on the selected channel is interrupted. The pulse width (o) is lengthened by each memory cycle and the memory content is no longer changed. When the trailing edge of the pulse (o) appears immediately after the channel pulse of the channel which is being read out the binary B will switch to the state 1 for the longest time interval and the pulse (ok) will trigger the univibrator UV~ through the integrator. The voltage on the capacitor C becomes equal to the reference dc voltage. Through the binary B~ the source of constant current i is opened, but the charging of C is not yet performed because Ka is still open. By triggering the univibrator UV 2 the capacitor C is being charged by constant current and therefore the pulses (ok) start to change the channel content. In the readout of the digital system the switch P1 is closed and the printing unit resets UV z. In this case the time interval required for the memory readout is: N
To = Z
[n(k)Tm+AT~,].
(4)
k=l
N is the number of memory channels, and n(k) is the channel content. The quantity A T~ is the time interval required between the readout of the preceding channel and the beginning of the readout of the next channel. On an average this time interval is 6 T m. The time diagram of the analog system s) is shown in fig. 4. When the analog system is in operation the
156
v. BONA(~Id
m-11 Tp UV1 MEMORY CYCLES
im÷l
]
The duration of the quasistable state of UVz depends on t h e ' m a x i m u m channel content,
Mt h CHANNEL READ-OUT
I_
k
T V = S T m -~ T W.
',i'lll!'',", ,,,
I
S is the maximum channel content represented in decimal form and Tw is the time required for the stabilization of the deflection of the pen recorder.
I-
/
UV2
.I
I I I.
'Ari
A ///
t ' ANALOG VOLTAGE I
I Fig. 4. Time diagram of the analog system. switch P1 is opened'and the duration of the readout process determines the]duration of the quasistable state Tv of the univibrator UVz. The duration of the quasistable state of the univibrator UV1 is Tp. By the arrival of the pulse CE which signals that the channel is empty, the source of constant current is closed. The pen recorder W deflects proportionally to the voltage on the capacitor C. The voltage on the capacitor C is an analog representation of the content of the readout channel. By switching back UV2 to its stable state through the relay R a spark is generated which records the position of the pen of the recorder W. The time required for the readout by the analog system is: N
T. = NTv+ Z AT;. k=l
(6)
(5)
3. Conclusion From the preceding analysis we may point out some advantages of the system described. The system enables one to obtain accurate and well arranged results. The readout of the selected channel is reliable and the transfer to the readout of the next channel can be identified with certainty. Also, owing to the automatic control the operation of the circuit for amplitude-to-time conversion in G I is simplified. Furthermore, the whole system consists of only a few components and is reliable in operation.
The basic idea for this system was given by Dr. M. Konrad. The author is grateful to him for useful advice and m a n y helpful discussions. References 1) R. C. McCall, Nucl. Instr. and Meth. 13 (1961) 92. 2) V. N. Kosti6, Bulletin "Boris Kidric" ll (March, 1961) 105. 3) H. Ostertag et al., Nucl. Instr. and Meth. 16 (1962) 310. 4) V. Bona~i6, Elektroteknika, (1965, Zagreb, in press). 5) M. Konrad and B. Sou~ek, ETAN (1962).
INSTRUMENTS
A N D M E T H O D S 42 (1966) I54-I56; © N O R T H - H O L L A N D
PUBLISHING
CO.
AN ANALOG AND DIGITAL READOUT SYSTEM FOR T H E CIRCULATING M E M O R Y V. BONAt~IC
Institute "Ruder Bo'~kovi~", Zagreb, Yougoslavia Received 10 January 1966 An analog and digital readout system for the circulating memory of a pulse-height analyzer is described and analyzed. Simultaneously one obtains here the spectrum display by the analog system and precise knowledge of the number of pulses in each channel by the digital system. The spectrum display is recorded
1. Introduction Logic circuits used in circulating memory pulseheight analyzers are usually simpler than the circuits of their readout systems1-3). The advantages of the described readout system are the simplicity of its logic and improved reliability. In this analog and digital system the readout is performed by subtracting unity by each memory cycle from the content of a selected channel. Thus the content of the selected channel is changed into a pulse train which is counted by a decimal counter. Simultaneously with the pulse train the capacitor is being charged by a constant current. When the channel content becomes equal to zero it is registered in decimal notation on the decimal counter and represented in analog form by the voltage on the capacitor. The two systems can display the content simultaneously as well as separately. In the digital system the channel content is represented in decimal notation and printed by a mechanical printer. In the analog system the content is changed into the analog voltage which deflects the pen of the recorder. Pulses performing the subtraction of unity from the channel content change the content of the observed channel only. After the readout of the content of a selected channel the transfer to the next channel is ensured by reliable identification of this transfer. Fig. 1
r
K
A
I
t. 2°
2~o - . . . .
ko ~ tZR,~1
I ,.11 o
~
l
[
I
r
I ~kn+l
C ....J" .....
Fig. 1. Time sequence diagram.
1
C J
by a pen recorder, whereas the channel content is printed by the digital system in decimal notation on paper tape. The advantages of the described readout system are the simplicity of its logic and reliability in work.
I
I
ok i
Fig. 2. Diagram of the pulse generator.
shows thecirculating memory cycle which starts by the reference pulse r. The channel content is recorded in binary notation .and the pulses representing it are synchronized with respect to the reference pulse. The channel K o is always empty and therefore the readout of its content is not performed. The logic of the readout system provides conditions for such an operation of the system. After the readout of the last channel the memory content is no longer changed.
2. Description and analysis The block diagram of a digital and analog system for the circulating memory readout is shown in fig. 3. The system consists of a pulse generator GI, which generates pulses for the subtraction of unity from the content of a selected channel, a logic for the digital and analog system, a pen recorder W for recording the spectrum display in analog form. A printing unit is used for printing the content in decimal form. The printing unit contains two counters and a mechanical printer. The ordinal number of the channel is recorded on the first counter, whilst the channel content is recorded on the second counter. The printer prints the content in decimal form from the counters onto paper tape. The pulse generator GI is shown in fig. 2. A detailed analysis of its operation is given in 4). After the pulse 154
AN
_~-7.- r
1
-
I°
L
ANALOG
AND
I
DIGITAL
READOUT
155
SYSTEM
of the observed channel becomes shorter than the delay time tz, the pulse (ok) passes through the anticoincidence A K and through the coincidence K and triggers the univibrator UV. During its quasistable state (Tu) the capacitor Ca is discharged by the constant current ii and therefore the duration of the pulse (o) is shortened by the amount:
I
t b = A2t o = (in/ik)B--(1/ik)C ; B : (Ck/Ca)Tm;
C = (Ck/Ca)Tni i.
(2)
The condition for the automatic holding on the desired channel is determined by the inequality: Tk -- (TB,ml,+ tb) > tz > ta + TBomln. i
IMEMORY
Fig. 3. Diagram of the analog and digital read out system. analysis the switch P is closed and the readout process is started. The capacitor Ca is charged by the current i~. During the memory dead time m the voltages on the capacitors Ca and Ck become equal through the linear coincidence LK, C a > Ck. The capacitor Ck is discharged by the current i k. The pulse width (o) at the output of the discriminator D is proportional to the voltage on the capacitor Ck and by each memory cycle it is increased by the amount: ta = Alto = (in/ik)A;
A = (Ck/Ca)T m.
(1)
The quantities ofeq. (1) are given in figs. 1 and 2. When the trailing edge of the pulse (o) appears after the channel pulse k o the readout of the content of the first channel starts. To perform the readout of a channel, the trailing edge of the pulse (o) should appear before the channel pulse of the channel to be read out and after the preceding channel pulse. By the trailing edge of the pulse (o) the binary B is switched to the state 1. The pulse k switches back the binary B to the state zero and the pulse (ok) is generated. The pulse (ok) passes through the coincidence Kz, subtracts unity from the channel content and adds unity to the counter content for channels in the printing unit. The trailing edge of the pulse (o) is held by automatic control through the pulse generator GI, between two channel pulses until the selected channel is read out. When the interval between the trailing edge of the pulse (o) and the channel pulse
(3)
The quantities TBom~n and TBlmi. ensure the triggering of the binary B to occur. The other quantities are given in fig. 1. After the readout of the selected channel the channel content becomes equal to zero. The circuit for the identification of zero in the arithmetic circuit of the analyzer produces the pulse CE. The binary B 1 is switched to the state 1, unity is added to the counter for recording the ordinal number of the channel, and the automatic control for holding the pulse on the selected channel is interrupted. The pulse width (o) is lengthened by each memory cycle and the memory content is no longer changed. When the trailing edge of the pulse (o) appears immediately after the channel pulse of the channel which is being read out the binary B will switch to the state 1 for the longest time interval and the pulse (ok) will trigger the univibrator UV~ through the integrator. The voltage on the capacitor C becomes equal to the reference dc voltage. Through the binary B~ the source of constant current i is opened, but the charging of C is not yet performed because Ka is still open. By triggering the univibrator UV 2 the capacitor C is being charged by constant current and therefore the pulses (ok) start to change the channel content. In the readout of the digital system the switch P1 is closed and the printing unit resets UV z. In this case the time interval required for the memory readout is: N
To = Z
[n(k)Tm+AT~,].
(4)
k=l
N is the number of memory channels, and n(k) is the channel content. The quantity A T~ is the time interval required between the readout of the preceding channel and the beginning of the readout of the next channel. On an average this time interval is 6 T m. The time diagram of the analog system s) is shown in fig. 4. When the analog system is in operation the
156
v. BONA(~Id
m-11 Tp UV1 MEMORY CYCLES
im÷l
]
The duration of the quasistable state of UVz depends on t h e ' m a x i m u m channel content,
Mt h CHANNEL READ-OUT
I_
k
T V = S T m -~ T W.
',i'lll!'',", ,,,
I
S is the maximum channel content represented in decimal form and Tw is the time required for the stabilization of the deflection of the pen recorder.
I-
/
UV2
.I
I I I.
'Ari
A ///
t ' ANALOG VOLTAGE I
I Fig. 4. Time diagram of the analog system. switch P1 is opened'and the duration of the readout process determines the]duration of the quasistable state Tv of the univibrator UVz. The duration of the quasistable state of the univibrator UV1 is Tp. By the arrival of the pulse CE which signals that the channel is empty, the source of constant current is closed. The pen recorder W deflects proportionally to the voltage on the capacitor C. The voltage on the capacitor C is an analog representation of the content of the readout channel. By switching back UV2 to its stable state through the relay R a spark is generated which records the position of the pen of the recorder W. The time required for the readout by the analog system is: N
T. = NTv+ Z AT;. k=l
(6)
(5)
3. Conclusion From the preceding analysis we may point out some advantages of the system described. The system enables one to obtain accurate and well arranged results. The readout of the selected channel is reliable and the transfer to the readout of the next channel can be identified with certainty. Also, owing to the automatic control the operation of the circuit for amplitude-to-time conversion in G I is simplified. Furthermore, the whole system consists of only a few components and is reliable in operation.
The basic idea for this system was given by Dr. M. Konrad. The author is grateful to him for useful advice and m a n y helpful discussions. References 1) R. C. McCall, Nucl. Instr. and Meth. 13 (1961) 92. 2) V. N. Kosti6, Bulletin "Boris Kidric" ll (March, 1961) 105. 3) H. Ostertag et al., Nucl. Instr. and Meth. 16 (1962) 310. 4) V. Bona~i6, Elektroteknika, (1965, Zagreb, in press). 5) M. Konrad and B. Sou~ek, ETAN (1962).