JPS62134565A - Apparatus for measuring current - Google Patents

Abstract

PURPOSE:To prevent a response speed from becoming slow in both of the measurement of a minute current and that of a low current region, by measuring a current to be measured even by the output signal of a differentiation means differentiating an analogue signal. CONSTITUTION:A differentiation means 27 for timewise differentiating the analogue voltage signal V outputted from an integrating circuit is provided to an I/F converter type current measuring apparatus and constituted of an A/D converter means 20, latch circuits 23, 22 as first and second memory means for storing the conversion results due to the converter means according to converted order, a substractor circuit 24 as a subtraction means outputting a signal corresponding to the difference between the memory contents of both memory means, a latch circuit 25 and a timing circuit 21. When an input current Im to be measured is measured, even if the cycle T1 of a pulse signal 2 becomes long and the response of measurement by a display device 6 becomes inferior, the measurement by the display device 6 is performed at a cycle T2 shorter than the cycle T1. Therefore, the measurement of a low current region can be performed without bringing about the lowering in response.

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] The present invention involves converting a current into pulses using an I/F converter that converts a current into a pulse train with a frequency proportional to the value of the current, and counting the pulses. The present invention relates to a current measuring device for an I/F converter that measures current over a wide range and with high precision, and in particular to a device configuration that does not slow response speed even when measuring a low current region or measuring a minute current in a wide range measuring device.

[Prior art and its problems]

When trying to measure current with high precision, there is a method of digital measurement using an A/D converter, but in this case, the maximum bit number of commercially available A/D converters is currently 16 bits, The accuracy of digital measurements is at most 10 degrees. However, &'i6-7 devices are used, for example, in radiation measurement.

Fig. 3 is a block diagram of such a conventional current measuring device.
The F converter 3 is a clock pulse generator that outputs a clock pulse 3a having a predetermined time width τl at every predetermined time interval τ2. 5 is pulse signal 2 and clock pulse 3
il! which is output from the clock pulse generator 3 every time the clock pulse 3a is output. l @
When the signal 3b is input, the count contents are displayed on the digital display 6.
This is a BCD counter whose counted contents are cleared when transferred to the BCD counter. Reference numeral 7 denotes a first display means consisting of the various parts shown in the figure except for the I/F converter 1.

Since each part of the indicating means 7 is configured as described above, the 1 indicator 6 displays the number of pulses outputted from the gate 4 during the time τl, and this number of pulses is calculated from the above-mentioned point. As is clear, the current Im is proportional to the current Im, so the current Im can be measured using the display 6.

In FIG. 3, the measurement is performed as described above, so in such a measuring device, the current Im can be controlled over a wide range and with high precision by increasing the number of conversion digits in the I/F converter and the number of display digits on the display 6. Currently, 7& current measurements can be carried out in the range of about 6 to 7 digits.

FIG. 4 is a block diagram of the I/F converter 1 shown in FIG. 3, where 8 is an integrating circuit which receives a current Im and outputs an analog voltage V proportional to the time-integrated value of this current. C1 is the integrating capacitor in this integrating circuit,
'The voltage V is input to the comparator 9,
The output of the flip-flop circuit 100 set terminal 10a
has been entered. Reference numeral 11 denotes an output circuit that amplifies the power of the output signal tOC of the flip-flop circuit 10 and outputs a signal having the same waveform as the amplified signal as the pulse signal 2 shown in FIG. I2 is controlled by the output signal tOC, and when the signal tOC is at H level, the current Im is input to terminal 1.
A constant value current is sucked out from 3 and passed to ground I4, and when signal 10c is at L level, terminal 13 and ground 14 are connected.
It is a constant current source that reduces the current flowing between the 15 is controlled by the output signal tOC, and when the signal tOC is at the H level, it charges the capacitor C2 connected to the inverting input terminal of the humparator 16 with a constant value 2'm current, and the signal tOC is at the L level. This is a constant current source that short-circuits and discharges capacitor C7. A reference voltage -vr is connected to the non-inverting input terminal of the comparator 16, and the output signal of the comparator 16 is further input to the reset terminal 10b of the flip-flop circuit.

Next, the operation of the converter shown in FIG. 4 will be explained using the time chart shown in FIG. 5. Since the I/F converter l is configured as described above, the waveform of the pulse signal 20 is equal to the waveform of the output signal 10c of the flip-flop circuit. Assume that the current Im is input to the terminal 13 in a stepwise manner at all times t1. Immediately before time t1, the output voltage EEV of the integrating circuit becomes a positive voltage V1 due to a mechanism not shown.
The output signals of the comparator 9 and the flip-flop circuit 10 are both at H level, the currents I, , I, are both zero, and the capacitor C! is short-circuited, the voltage between the terminals of C7 is zero volts, and the output of the comparator 16) is at the L level. When t + t I m is input at time t1, the voltage V changes at a constant rate of change d V / d t = I rn /
When the voltage V decreases at C+ and reaches zero volts at time t2, the comparator 9 operates and the output signal 10C of the 70-to-1 circuit of the knob 71J becomes H level. When the signal tOC becomes H level, currents I,,I, flow, so [aE Vkt,
-fflf rate [dV/d t = (Im-I,)/C
8, and in this case I m (I is set to be ), the voltage of C1 also has a constant rate of change d V/d
It decreases at t=It/Ct. Since the voltage V increases, the output level of the comparator 9 returns immediately. C at time t3! When the voltage reaches -Vr, comparator 1
6 operates and the signal tOC becomes L level.

When the signal tOC goes to L level, the currents I, , I, both become zero and C! is shorted, so the voltage V is again dV
/dt=Im/C, and the voltage of C2 increases toward zero volts. When the voltage V becomes zero volts again at time t4, the above series of operations is repeated again. Since the I/F converter 1 operates as described above,
At time t2, a pulse-like signal toe with a time width τ3 (=t, -i, ) is output, and this pulse-like signal t
OC, in other words, the pulse signal 20 frequency F is I, = I,
If it is set as (expressed by equation 11).

F=Im/(Vr-C,) -----...(1
) Therefore, (as is clear from equation 11, converter l is a converter that outputs pulse signal 2 with a frequency proportional to current Im.

Reference numeral 17 in FIG. 4 consists of the various parts shown except for the integrating circuit 8, to which the analog voltage signal V is input.

This control circuit outputs the pulse signal 2 with a frequency F proportional to the current Im as described above, and drives the integrating circuit 8 so that the voltage V is reset each time the pulse signal 2 is output. That is, the I/F converter l is composed of an integrating circuit 8 and a control circuit 17. T in Figure 5
, is the period of signal toe or signal 2 and 'I'1=I/F
It is clear that

In Fig. 3, the current is measured as described above.
This device has problems as explained below when the measurement range is widened (that is, when it is used as a wide range measuring device) and when measuring minute currents.

ωFor a wide range measurement device; For example, if the highest frequency output of the I/F converter is 1oOcKHz and a current measurement device that can measure 7 digits without gain switching is obtained, the lowest frequency of the output of the I/F converter is 0.01(H
z), and in this case, the 20 cycles of the pulse signal are 100 seconds. That is, such a current measuring device has a problem in that the responsiveness during measurement in a low current range is very poor.

(2) In the case of microcurrent measurement: For example, a microcurrent of 1 to 104 CpA, such as the ionizing current of an ionization chamber in radiation measurement.
) to t -to' (Hz) K using a converter/F converter, the capacitance of capacitor C2 in the integrating circuit is changed to 1 (1
) F), constant current source 12.15 0 The capacitance of C0 will deteriorate due to the effects of noise and stray capacitance that occur when switching the current, and the conversion operation will become unstable. needs to be made larger. For this reason CI
is normally set to a fairly large value, but in this case, the above-mentioned rate of change of voltage V, dV/dt=Im/C, becomes smaller, and as a result, the I/F conversion speed becomes slower. That is, in this case as well, the above-described current measuring device has the problem of poor responsiveness.

[Purpose of the invention]

The present invention solves the problems of the conventional I/F converter type current measurement device as described above, and improves response speed in both low current range measurement and minute current measurement in a wide range measurement device. An object of the present invention is to provide an I/F converter type current measuring device that never becomes unusable.

[Key points of the invention]

In order to achieve the above object, the present invention includes an integrating circuit for integrating the current of the object to be measured, and a control circuit that receives an analog signal output from the integrating circuit and outputs a pulse signal with a frequency proportional to the value of the current of the object to be measured. , and differentiating means for differentiating the analog signal, and the current to be measured is also measured based on the output signal of the differentiating means. According to the present invention, with this configuration, measurement is performed using the output signal of the differentiating means both when measuring a minute current or when measuring a low current region in a wide range measuring device, thereby increasing the response speed. An I/F converter type current measuring device that does not become slow can be obtained.

[Embodiments of the invention]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a time chart illustrating the operation of the embodiment of FIG. The configuration and operation of the embodiment shown in FIG. 1 will be explained below using FIGS. 1 and 2. In both figures, 18 starts timing when the pulse signal 2 is input, and sends a signal tSa having the same waveform as the signal 2 at predetermined time intervals T as an A/D conversion command signal to the A/D conversion circuit 191C. This is a timer circuit that outputs. 19, when the signal 18a is input, the integration circuit 8 of the I/F converter 1 is activated at the fall time of the signal.
to the value of the analog voltage signal V output from. A/
This is an A/Df conversion circuit that starts D conversion, and when this A/D conversion is completed, outputs a data signal L9a according to the conversion result and also outputs a pulsed conversion completion signal L9b.

The A/D conversion circuit [9 is configured such that the output signal 19a is cleared at the fall of the conversion command signal 18H.

20 consists of a timer circuit 18 and an A/D conversion circuit 19, and converts the analog signal V into A at a predetermined period T as described above.
This is an A/D conversion means that performs /D conversion.

Reference numeral 21 denotes a timing circuit into which the pulse signal 2 and the conversion completion signal L9b are input, and outputs pulse-like launch signals 21al, 2tbe, and 2LC at the timings described below.
Every time the conversion completion signal 19b is input to 1, the signal 19
Pulse signal that rises at the fall of b, latch signal 2
1b, after the pulse signal 2 is input to the timing circuit 21, the conversion completion signal 19b that is outputted from the A/D conversion circuit 19 first is inputted to the timing circuit 21, and then the conversion completion signal 19b that is outputted subsequently is inputted to the timing circuit 21. A pulse signal that rises at the rising edge of signal 19b.

The latch signal 21C is a pulse signal that rises at the falling edge of the signal 21a every time the launch signal 21a following the latch signal 218 that is first output from the timing circuit 21 is output after the pulse signal 2 is input to the timing circuit 21. It is. 22 is the data signal 19a and the latch signal 2
1a is input, and when the signal 21a falls, the data signal 19a at that time is stored and the lunch data signal 22a is generated.
This is a latch circuit that outputs as . 23 receives the latch data signal 22a and the latch signal 21b, and the signal 21
This is a latch circuit that stores the latch data signal 22a at that time at the falling edge of signal b and outputs it as a latch data signal 233. 24 is a subtraction circuit that calculates the +7) difference between the latch data signal 23a and the latch data signal 22a, and outputs the result of this calculation as a signal 24a. The output signal 24a of the subtraction circuit is sent to the latch circuit 25 together with the latch signal 21C.
When the latch signal 21C falls, the latch circuit 25 stores the value of the signal 24a at that time and outputs a signal 25a to the digital display 26 in accordance with the memorized result.

In FIG. 1, if pulse signal 2 rises at time t2 as described above in [7], then after this time! Pressure V
The voltage V rises at dV/clt=(Im-It)/C+, and when pulse signal 2 falls at time t3, the voltage V falls at dV/dt=Im/C1 from time t2, and from time t2 At time t4, which has elapsed by T, the voltage V starts to rise again. Almost at the same time as the pulse signal 2 is output at time t2, the conversion command signal tea is output, and the value vI of the voltage V at time t3 is A/D converted by the A/D conversion circuit 19. When the D conversion is completed, a conversion completion signal 19b is outputted, and a data signal 19a corresponding to the data IK, which is the conversion result, is outputted.

After the conversion completion signal 19b is output, the latch signal 2
1a is output, the output signal 22 of the latch circuit 22
a becomes a signal corresponding to data 1.

At time [11], a time T (in this case, T2 < T) has elapsed from time t2.

Further, the timer circuit 18 outputs a conversion command signal 18a. Therefore, the value of voltage V at time t12 is A
When the A/D conversion is completed, the conversion circuit 19 outputs a conversion completion signal 19b, and at the same time outputs a corresponding signal 19a as data 2, which is the conversion result. In this case, as soon as the signal L9b is input to the timing circuit 21, the latch signal 21b is output, so the latch circuit 23
stores the latch data signal 22a at the falling time t13 of the signal 21b and outputs it as the latch data signal 23a, but since the latch data signal 22a at this falling time t13 corresponds to data 91, The signal 23a output at time t13 is a signal corresponding to data RI1. Further, in this case, the timing circuit 21
outputs the latch signal 21a after outputting the latch signal 21b, so at time t14 when the signal 21a falls, the data signal 22a becomes a signal corresponding to data 2, and as a result, at time t14, the output signal 24a of the subtraction circuit becomes the data The signal corresponds to the difference between data 1 and data 2. When the latch signal 21a falls at time t14, the latch signal 21a
C rises, and this signal 21C falls at time t15, so at time t15, the output signal 25a of the latch circuit 25 corresponds to the difference between data l and data 2, that is, the voltage difference (Vl - v,). It becomes a signal.

At time t16Vc, when time Tt has elapsed from time tll, the timer circuit 18 outputs the conversion command signal 18a again, so first the data signal 19a becomes a signal corresponding to data 3, and then the data signal 23a becomes data 2. Then, the signal 22a becomes a signal corresponding to data 3, so after time t17 when the latch signal 21C rises, the output signal 24a of the subtraction circuit becomes a signal corresponding to the difference between data 2 and data 3. Become. data 3
is the digital conversion value of the voltage V at the fall time of the command signal 18a output at time t16. Therefore, at time t18 when the latch signal 21C falls, the latch data signal 25a becomes data 2 and data. In other words, it is a signal corresponding to the voltage difference (Vf Vs).

At time t4, when time Tt has not elapsed since time tlfi, pulse signal 2 is output as described above.

Therefore, at this time, the timer circuit 18 outputs the conversion command signal te.
a is output, the data signal 19a becomes a signal corresponding to data 4, and then the latch signal 21a is output, so the data signal 22a becomes a signal corresponding to data 4.
In this case, since neither the latch signals 21b nor 21c are output, the data signal 25a does not change. After the conversion command signal 18a is output at time t19, which is a time T that has elapsed from time t4, the latch signals 21bl 21al 21C
are sequentially output in this order, so that at falling time t20 of the signal 21C, the latch data signal 25a becomes a signal corresponding to the difference between data 4 and data 5.

As described above, in the apparatus shown in FIG. 1, at time t15, the signal 25a becomes a signal corresponding to (VtVt).

It is clear from Figure 2 that 5 K (v+Vt)=(
d V/d t) 11T, so equation (2) holds true.

Vl-V2 = (dV/dt)-Tt = (Im/C
t)"Tt -...- (21 As is clear from equation (2), the latch data signal 25a corresponds to the input current ImK to be measured in this case, and this theory is based on the time t18.t2.
This holds true for both 0 and 0. Therefore, by using the configuration shown in FIG. 1, the current Jm can be measured by any of the indicators 6, 26. As is clear from the above, the measurement by the display 26 is based on I
What is once integrated by the integrating circuit in the /F converter is differentiated again to obtain the measured value. In other words, as shown in FIG. 1, each part shown in the figure except the I/F converter 1, display means 7, and display 26 constitutes a differentiating means 27 that differentiates the analog signal V with respect to time, and this differentiator The means 27 includes an A/D conversion means 20 and latch circuits 23 and 2 as first and second storage means for storing the conversion results by the conversion means in the order of conversion.
2, a subtraction circuit 24 and a launch circuit 25 as subtraction means for outputting a signal corresponding to the difference between the respective storage contents in both storage means, and a timing circuit 21.

In FIG. 1, the input current Im to be measured is measured as described above, so even if the pulse signal 20 period T1 becomes longer and the responsiveness of the measurement by the indicator 6 becomes worse, the measurement by the 1 indicator 26 is still T. Since the current measurement lid can be used in a cycle T shorter than Measurements can also be similarly performed without reducing responsiveness.

In the above embodiment, the differentiating means 27 digitally differentiates the analog signal V, but it is clear that in the present invention, such differentiating means may be constructed using an analog differentiating circuit. .

Furthermore, in the above explanation, the display device 6.26 was used in combination, but depending on the object to be measured, it is possible to provide only the display device 26 and mainly measure low current areas or minute currents. What can be done is clear.

〔Effect of the invention〕

As described above, the present invention includes an integrating circuit for integrating the current to be measured, and a control circuit that receives the analog signal output from this integrating circuit and outputs a pulse signal with a frequency proportional to the value of the current to be measured. In a current measuring device using an I/F converter, a differentiating means for differentiating an analog signal is provided, and a current to be measured is measured using an output signal of the differentiating means. According to one aspect of the invention, therefore, by configuring in this manner.

By employing the output signal of the differentiating means when measuring minute currents or measuring low current regions in a wide range measuring device, it is possible to obtain a current measuring device that does not cause a decrease in response. be done.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of FIG. 1, and FIG. 3 is a configuration diagram of a conventional I/F converter type current measuring device. 4 is a block diagram of the I/F converter in FIG. 3, and FIG. 5 is a time chart for explaining the operation of FIG. 4. l...I/F converter, 2...pulse signal, 8...integrator circuit, 17...
...control circuit, Im...input current, ■.
...Analog voltage signal. 4th prisoner

Claims (1)

[Scope of Claims] 1) An integrating circuit that outputs an analog signal proportional to a time integral value of an input current to be measured, and an integrating circuit that receives the analog signal and outputs a pulse signal having a frequency proportional to the input current, and the pulse signal a control circuit that drives the integrating circuit so that the analog signal is reset each time the analog signal is output; and differentiating means for differentiating the analog signal with respect to time; A current measuring device characterized by measuring current. 2) In the current measuring device according to claim 1, the differentiating means includes an A/D converting means for A/D converting an analog signal at a predetermined period, and converting the conversion result by the A/D converting means into the the first and second to be stored according to the order of the cycles;
A current measuring device comprising: a storage means; and a subtraction means for outputting a signal according to the difference between the stored contents in both the storage means, and the output signal of the subtraction means is used as the output signal of the differentiating means. .