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Ion counting device with dead-time correction
Vacuum/volume37/numbers 1/2/pages 79 to 80/1 987
0042-207X/87$3.00 + .00 Pergamon Journals Ltd
Printed in Great Britain
Ion counting device with dead-time correction I B e r e c z , S B o h & t k a , Z D i b s , J G&I, G Langer and J M o l n & r , Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, PO Box 51, Hungary, H-4001
An ion counting device is described, which consists of a dead-time corrected ratemeter and a counter. The new type of dead-time correction appfied in the ratemeter makes possible high accuracy in the case of high counting rate. The different settings of the instrument can be controlled manually or by computer.
Introduction
R -
Dead-time effects can reduce the accuracy of counting high rate random events. The dead time is caused by different parts of the measuring chain: preamplifier, discriminator, ratemeter. Usually the dominant part of the dead time is generated by the ratemeter. In the case of ratemeters, the dead time is of so-called nonextended type. Denoting the input rate by R and the output rate by r the relation between the input and output rate for a nonextended dead time: r-
R
Realization of a dead time corrected ratemeter
The block diagram of a dead-time corrected ratemeter, constructed on the basis of the above considerations is shown in Figure 1. The input pulses trigger the non-retriggerable monostable multivibrator (MMV). The output pulses of the MMV are led to the dead-time averager (DTA), which produces an output voltage proportional to the relative dead time. The inverted signal of the MMV is led to the live-time averager (LTA) which produces a voltage proportional to the relative live time. The output signals of the DTA and LTA are led, respectively, to the numerator and denominator input of the ratio-to-frequency converter (RFC). The RFC produces an output frequency proportional to the ratio d/l, i.e. to the input frequency of the ratemeter. This output frequency partly is used for counting, partly it is averaged by the frequency averager (FA) producing an analog output signal.
where ~ is the dead time for one pulse 1' 2. Independently of the type of dead time the following simple formula can be applied: (2)
r = RI,
where I is the relative 'live' time. Similarly to I a relative dead time (d) can be introduced. I and d are related by: d = 1 - I.
(4)
Tl"
Ifz is constant, it can be considered, t h a t l / r is a scale factor and R can be calculated from the relative dead and live times. In practice both the relative dead and live times can be obtained by a simple averaging technique. By averaging the dead time pulses d and by averaging the inverted dead time pulses I can be found. Dividing d by l R can be determined.
(1)
1 +Rz
ld
(3)
Principle of dead-time correction
Comparing the relation (1) with the relation (2) and using relation (3), the following formula can be deduced. ! Dead - time averager j (DTA)
j
I I
input [M....I
Ratio - to -
Numeratof- J frequency Denominator ] converter
B- multivibrator (MMV)
[
A
Frequency output
(RFC)
7 Live - tune averager
(LTA)
Analog Frequency output averager(FA) 1
Figure 1. Block diagram of the dead-time corrected ratemeter.
79
I Berecz et al. Ion counting device with dead-time correction
Analog out
thgh vohage power supply
Multiplier tut~e
Prescaler on/off
-I w
('t',ar ge sensitive pre - a m p . a n d discriminator 1--
Presc~er
Time
R a t e n l e t er
Count Full mode scale
- -
Frequency divider
]
B
Selectt~
=
( oul/t0r
[
I I Time preset
[ illler
Digital out
Figure 2. Block diagram of the ion counting device.
Device description The block diagram of the ion counting device containing the above described dead-time corrected ratemeter is shown in Figure 2. The counter part of the device may count the randomly spaced pulses from the charge sensitive preamplifier and discriminator or the periodic pulse train from the ratemeter. The range of the ratemeter may be set in decade steps between 10 c s - t and 1 Mc s-~. The averaging time constant may be varied from 3.3 ms to 3.3 s in seven steps. The full range of the
80
frequency output of the ratemeter is 100 kHz. With the help of a frequency divider it may be 10 or 1 kHz, too. The pre-scaler extends the measuring range of the ratemeter to 10 M c s -1 The different settings (range, time constant etc.) can be controlled by a switch or with the aid of a computer.
References 1 j W MOiler, Nucl Instrum Meth, 112, 47 (1973). 2 j Gill and G Bibok, A T O M K I Bull, 24, 95 (1982).
0042-207X/87$3.00 + .00 Pergamon Journals Ltd
Printed in Great Britain
Ion counting device with dead-time correction I B e r e c z , S B o h & t k a , Z D i b s , J G&I, G Langer and J M o l n & r , Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, PO Box 51, Hungary, H-4001
An ion counting device is described, which consists of a dead-time corrected ratemeter and a counter. The new type of dead-time correction appfied in the ratemeter makes possible high accuracy in the case of high counting rate. The different settings of the instrument can be controlled manually or by computer.
Introduction
R -
Dead-time effects can reduce the accuracy of counting high rate random events. The dead time is caused by different parts of the measuring chain: preamplifier, discriminator, ratemeter. Usually the dominant part of the dead time is generated by the ratemeter. In the case of ratemeters, the dead time is of so-called nonextended type. Denoting the input rate by R and the output rate by r the relation between the input and output rate for a nonextended dead time: r-
R
Realization of a dead time corrected ratemeter
The block diagram of a dead-time corrected ratemeter, constructed on the basis of the above considerations is shown in Figure 1. The input pulses trigger the non-retriggerable monostable multivibrator (MMV). The output pulses of the MMV are led to the dead-time averager (DTA), which produces an output voltage proportional to the relative dead time. The inverted signal of the MMV is led to the live-time averager (LTA) which produces a voltage proportional to the relative live time. The output signals of the DTA and LTA are led, respectively, to the numerator and denominator input of the ratio-to-frequency converter (RFC). The RFC produces an output frequency proportional to the ratio d/l, i.e. to the input frequency of the ratemeter. This output frequency partly is used for counting, partly it is averaged by the frequency averager (FA) producing an analog output signal.
where ~ is the dead time for one pulse 1' 2. Independently of the type of dead time the following simple formula can be applied: (2)
r = RI,
where I is the relative 'live' time. Similarly to I a relative dead time (d) can be introduced. I and d are related by: d = 1 - I.
(4)
Tl"
Ifz is constant, it can be considered, t h a t l / r is a scale factor and R can be calculated from the relative dead and live times. In practice both the relative dead and live times can be obtained by a simple averaging technique. By averaging the dead time pulses d and by averaging the inverted dead time pulses I can be found. Dividing d by l R can be determined.
(1)
1 +Rz
ld
(3)
Principle of dead-time correction
Comparing the relation (1) with the relation (2) and using relation (3), the following formula can be deduced. ! Dead - time averager j (DTA)
j
I I
input [M....I
Ratio - to -
Numeratof- J frequency Denominator ] converter
B- multivibrator (MMV)
[
A
Frequency output
(RFC)
7 Live - tune averager
(LTA)
Analog Frequency output averager(FA) 1
Figure 1. Block diagram of the dead-time corrected ratemeter.
79
I Berecz et al. Ion counting device with dead-time correction
Analog out
thgh vohage power supply
Multiplier tut~e
Prescaler on/off
-I w
('t',ar ge sensitive pre - a m p . a n d discriminator 1--
Presc~er
Time
R a t e n l e t er
Count Full mode scale
- -
Frequency divider
]
B
Selectt~
=
( oul/t0r
[
I I Time preset
[ illler
Digital out
Figure 2. Block diagram of the ion counting device.
Device description The block diagram of the ion counting device containing the above described dead-time corrected ratemeter is shown in Figure 2. The counter part of the device may count the randomly spaced pulses from the charge sensitive preamplifier and discriminator or the periodic pulse train from the ratemeter. The range of the ratemeter may be set in decade steps between 10 c s - t and 1 Mc s-~. The averaging time constant may be varied from 3.3 ms to 3.3 s in seven steps. The full range of the
80
frequency output of the ratemeter is 100 kHz. With the help of a frequency divider it may be 10 or 1 kHz, too. The pre-scaler extends the measuring range of the ratemeter to 10 M c s -1 The different settings (range, time constant etc.) can be controlled by a switch or with the aid of a computer.
References 1 j W MOiler, Nucl Instrum Meth, 112, 47 (1973). 2 j Gill and G Bibok, A T O M K I Bull, 24, 95 (1982).