JP3469369B2 - Electric measuring instrument - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric measuring instrument capable of separating a power supply from a weak current operating section such as an arithmetic control section having a CPU (Central Processing Unit). 2. Description of the Related Art Conventionally, when determining the quality of a mounting board or the like, an electric measurement of an object to be measured is performed using a measuring instrument such as an in-circuit tester. At this time, a true value such as a resistance value cannot be directly measured. This is because, as shown in FIG. 6, the actual measured value is affected by the power supply frequency and changes as a waveform in which the power supply frequency is superimposed on the true value to be obtained as noise. Such a problem similarly occurs when a high resistance measuring instrument or a high input impedance measuring instrument is used. Therefore, in order to detect the power supply frequency, a power supply frequency detection circuit as shown in FIG. 7 is used. In the figure, 10 is a power frequency detection circuit, 12 is the commercial AC power supply, 14 is a resistor, 16 is a surge absorber,
Reference numeral 18 denotes a diode, and reference numeral 20 denotes a photocoupler including a light emitting diode 22 and a light receiving transistor 24. In addition,
The reason for using the photocoupler 20 is to insulate the side of the power supply 12 from the side of the weak current operation unit such as the arithmetic control unit 26 having the CPU. When such a power supply frequency detecting circuit 10 is used, the power supply voltage is limited to a voltage level which can be applied to the light emitting diode 22 by the resistor 14, the noise contained in the power supply is absorbed by the surge absorber 16, and the power supply voltage is A half-wave of one cycle of the frequency can be applied to the light emitting diode 22 and transmitted to the light receiving transistor 24. Then
Since a pulse waveform as shown in FIG. 8 is generated as an output of the power supply frequency detection circuit 10, the analog-to-digital conversion is performed by the AD converter 28, and the “H” state is read by the arithmetic control unit 26. At that time, the power frequency is 60H
The time of T corresponding to one cycle differs depending on whether z or 50 Hz. For example, in the case of 60 Hz, T is 16.6 ms, 5
In the case of 0 Hz, the time is 20 ms.
Can be used to determine the power supply frequency. The voltage taken into the arithmetic control unit 26 is reduced to a low voltage, for example, 5V. Then, based on the determined power supply frequency, the DUT is sampled at intervals of Δt for one cycle as shown in FIG. 9 and the measured values of N times are averaged to obtain a true value. Is found. However, when the power supply frequency is 60 Hz or 50 Hz, if an integral type is used for the A / D converter for converting the measured value from analog to digital, a measurement signal for 100 ms corresponding to 6 cycles at 60 Hz and 5 cycles at 50 Hz , The true value can be obtained without first obtaining the power supply frequency. However, in this method, the measurement time is too long, such as 100 ms. [0004] However, when such a power supply frequency detecting circuit 10 is used, a voltage of 100 V near a weak current operating unit such as an arithmetic control unit 26 provided with a CPU.
In such a case, the commercial AC power supply 12 must be drawn in, and the weak current operation section is likely to malfunction due to the influence of power supply noise. Moreover, the provision of the dedicated power frequency detection circuit 10 makes the product expensive. On the other hand, when the power supply frequency detection is unnecessary, the measurement time is too long. The present invention has been made in view of such a conventional problem. A weak current operation section such as an arithmetic control section having a CPU is hardly affected by power supply noise, and the product is inexpensive. It is an object to provide an electric measuring instrument having a short measurement time. Means for solving the above problems will be described with reference to FIG. 1 which clearly shows the present invention. This electric measuring instrument is attached to the same DUT at an earlier stage, at an arbitrary time, and 8.3 ms after the arbitrary time, 10 m
A measuring means 40 is provided for measuring each electric value of the same kind after 16.6 ms after s. Then, in the middle, the average value of the measured value at that arbitrary point and the measured value after 8.3 ms is calculated, and 8.3 is further calculated.
An average value calculating means 42 for calculating an average value of the measured value after 1 ms and the measured value after 16.6 ms, and an average value comparing means 44 for judging whether or not the two average values are equal to each other are provided. When the average values are equal, the average value is determined as the true value, and when both average values are different, the average value of the measurement value at any time and the measurement value after 10 ms is calculated, and the average value is determined as the true value. And a true value determining means 46 for determining. Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a block diagram showing a functional configuration at the time of measurement of the in-circuit tester to which the present invention is applied. In the figure, 30 is an arithmetic control unit, 32 is a measuring unit, 34 is a scanner, 36 is an A / D converter, and 38 is an object to be measured. The arithmetic control unit 30 controls the measurement by giving control signals to the measuring unit 32, the scanner 34, the A / D converter 36, and the like at the time of measurement, and executes the arithmetic operation. The CPU, ROM (read only memory), RAM
(Read / write memory). The measuring section 32 is a section for performing various electrical measurements by applying a constant voltage to the device under test 38 via the scanner 34 or flowing a constant current thereto. Source. The scanner 34 measures a large number of objects 38 to be measured, and the measuring unit 32 and the large number of objects 3
8 are connected in common, and the DUT 3
This is a device that performs measurement by switching to 8 and has many relays. The A / D converter 36 converts the analog value measured by the measuring unit 32 into a digital value and converts the analog value into a digital value.
It is a device that gives 0. Incidentally, the measured object 38 is a resistor,
Capacitors, coils and the like. Next, the operation of the in-circuit tester at the time of measurement will be described. FIG.
It is a flowchart consisting of steps P1 to P11 showing an operation by a true value determination processing program stored in an AM or a ROM. In the measurement, the tips of probe pins (not shown) connected to the respective measurement branch lines of the scanner 34 come into contact with designated positions of a large number of the DUTs 38, respectively. Then, the processing by the program is started, and P is first set for one DUT 38 to be measured.
At step 1, the electric value M1 at an arbitrary time point t0 is measured. At this time, for example, the resistance value R is calculated from the constant voltage value V generated in the measurement unit 32 by the arithmetic control unit 30 and the measured current value I as R = V /
It is calculated from the formula of I. Next, the flow goes to P2, and the same electric value M2 of the same DUT 38 is measured 8.3 ms after the arbitrary time t0. Then, the process goes to P3, and the same measurement is performed to obtain a measured value M3 10 ms after the arbitrary time t0. or,
Go to P4 to obtain the measured value M4 16.6 ms after the arbitrary time t0. Thus, 8.3 m from the arbitrary time point t0
s, 10 ms, and 16.6 ms, the measured values M2, M3,
M4 is obtained when one cycle is 16.6 ms, half cycle is 8.3 ms when the power supply frequency is 60 Hz, and 50 Hz
In this case, it is considered that one cycle is 20 ms and a half cycle is 10 ms. Therefore, using the waveform obtained by plotting the measured value M as the time t elapses as shown in FIG.
The correspondence between 6.6 ms and each of the measured values M1, M2, M3, M4 is shown. Note that is t0, and t0 + 8.3.
ms, t0 + 10 ms, and t0 + 16.6 ms, respectively. Next, the flow goes to P5, where the measured value M at an arbitrary time t0 is obtained.
From 1 and the measured value M2 8.3 ms after the arbitrary time point t0, the average value M12 of them is calculated by the formula of M12 = (M1 + M2) / 2. Next, go to P6, and 8.3 from an arbitrary time point t0.
From the measured value M2 after ms and the measured value M4 16.6 ms after the arbitrary point in time t0, the average value of those values M24 is calculated as M24 = (M2
+ M4) / 2. Next, the process goes to P7, and it is determined whether the average values M12 and M24 are equal. Then, as shown in FIG. 5, the measured values M1 and M
4 are equal, the power supply frequency is 60 Hz and YEs
Is determined. Then, go to P8 and set the power frequency to 60
Hz. Next, the process goes to P9, and the average value M12 calculated in the previous step P5 is determined as the true value M0. Note that the average value M24 may be determined as the true value M0. If NO, the power frequency is 50 Hz, go to P10, and the power frequency is 5
Determine to be 0 Hz. Next, the process goes to P11, and from the measured value M1 at an arbitrary time point t0 and the measured value M3 after 10 ms, an average value M13 thereof is calculated from the equation of M13 = (M1 + M3) / 2.
The average value M13 is determined as the true value M0. It is not always necessary to determine the power supply frequency by providing steps P8 and P10, and the true value M0 may be directly obtained based on the determination result of P7. According to the present invention described above, a true value can be obtained by four samplings without knowing the power supply frequency. Therefore, it is not necessary to use a dedicated power supply frequency detection circuit or the like, and it is possible to separate the commercial AC power supply, which is a noise source, from the weak current operation unit, thereby improving measurement accuracy. In addition, the cost of the product is reduced and the measurement time is shortened.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an electric measuring instrument according to the present invention. FIG. 2 is a block diagram showing a functional configuration at the time of measurement of an in-circuit tester to which the present invention is applied. FIG. 3 is a flowchart showing an operation according to a true value determination processing program stored in a memory provided in an arithmetic control unit of the in-circuit tester. FIG. 4 is a diagram showing a correspondence relationship between each designated measurement time point and each measured value for a measured value waveform by the in-circuit tester. FIG. 5 shows a power supply frequency of 6 using the in-circuit tester.
It is a figure which shows that the measured value at an arbitrary point and the measured value after 16.6 ms are equal about the measured value waveform in the case of 0 Hz. FIG. 6 is a diagram showing a relationship between an actual measurement waveform affected by a power supply frequency and a true value which is a measurement value to be obtained. FIG. 7 is a diagram showing a connection relationship between a conventional dedicated circuit for detecting a power supply frequency required for measurement and an arithmetic control unit for capturing the power supply frequency. FIG. 8 is a diagram showing an output waveform of the power supply frequency detection circuit. FIG. 9 is a diagram showing sampling points performed to obtain a true value for a measurement waveform for one cycle. [Explanation of Symbols] 30: arithmetic control unit 32: measuring unit 34: scanner 3
6 ... A / D converter 38 ... DUT 40 ... Measurement means 42 ... Average value calculation means 44 ... Average value comparison means 46
… True value determination means

Claims (1)

(57) [Claims 1] Regarding the same DUT, at an arbitrary time, and 8.3 ms, 10 ms, and 16.
A measuring means for measuring each electric value of the same kind after 6 ms, an average value of the measured value at any time point and the measured value after 8.3 ms is calculated, and the measured value after 8.3 ms and 16.6 ms after The average value calculation means for calculating the average value of the measured values, and the average value comparison means for determining whether both average values are equal, and when both average values are equal, determine the average value as a true value, When the two average values are different, an electric measurement characterized by comprising a true value determining means for calculating an average value of a measured value at an arbitrary time point and a measured value after 10 ms and determining the average value as a true value. vessel.