JPS63205572A - Error preventing circuit for voltage measurement - Google Patents

Abstract

PURPOSE:To speed up measuring operation by removing an error in measured voltage due to equivalent stray capacity which is present on the side of the input bus of an A/D converter by a discharging circuit. CONSTITUTION:The discharging circuit 7 is constituted by interposing the series circuit of a resistance R and a relay contact point rs between the ground and a bus 10 connected from a multiplexer MPX to a DC measuring instrument DCM closely to the input terminal 9 of the A/D converter of the bus 10. Then a driving pulse Ps with a period T is applied to the contact point rs at the time of voltage measurement, and consequently the contact point rs is turned on to set the voltage at the terminal 9 to a zero state temporarily. Then the voltage V1 of a measurement object point 11 is inputted to the A/D converter. Even when a voltage V2 at a next measurement object point 12 is inputted to the A/D converter, the contact point rs is turned on with the pulse Ps before the voltage V2 is measured to clear the remaining voltage at the time of the voltage V1 to a zero state temporarily, and a DC voltage is inputted to the measuring instrument DCM. Namely, the contact point rs is operated associatively with the switching of switches RS1-RSN of the multiplexer MPX to clear remaining charges due to the stray capacity of the bus 10.

Description

[Detailed Description of the Invention] [Summary] - For example, a printed circuit board assembly is used as a test object, and the power supply voltage, element operating voltage, etc. of the test object are measured using a multiplexer and an analog-to-digital (A-D) converter. In the measurement circuit, the measurement voltage error (residual voltage error) due to the equivalent stray capacitance existing on the input bus side of the A-D converter is
By removing it with a discharge circuit, the measurement error can be reduced to 1/100.
Keep it to 0 or less.

In addition, the aim is to speed up the measurement.

[Industrial application field]

The present invention relates to a voltage measurement error prevention circuit in a printed circuit board tester or an IC tester.

When testing a printed circuit board assembly with multiple voltage checkpoints as the test object.

This eliminates errors caused by stray capacitance in test cables or measurement input buses, increasing test speed and reliability.

(Conventional technology) FIG. 3 is a block diagram showing a conventional voltage measurement circuit.

Moreover, FIG. 4 is a time chart during voltage measurement.

In Figure 3, 11.12. -.-3n are measurement target points of the main board circuit, which are respectively used as voltage check points for power supply or element operation.

MPX is a multiplexer equipped with a switch that sequentially scans a plurality of voltages to be measured, RsI, Rs2..., Rsn.

"DCM is a DC voltage measuring device that is connected to the output side of the multiplexer IPX. This measuring device converts the analog voltage to be measured into a digital signal and outputs it through terminals Do and D.
1, o2--On.

The operation of the circuit shown in FIG. 3 will be explained with reference to the time chart shown in FIG.

That is, the measured voltage waveform is shown in which the measurement target points are sequentially switched by the multiplexer and the output of the bus 10 is input to the AD converter of the DC voltage measuring device.

The time chart shows the switch R depending on the period T on the 1-hour axis.
sl is turned on, then switch Rs2 is turned on, and then Rs
3 is turned ON, the scanning is repeated, but first, the voltage v1 of the measurement target point 11 is input to the A-D converter,
Subsequently, the voltage v2 at the point to be measured 12 is input, and further the voltage v at the point to be measured 13 is input.

These voltages will be converted from analog to digital.

However, R31R3! -Rsn switch operating period T
During I, the voltages at measurement points 11, 12, .

[Problem that the invention seeks to solve]

For example, if the measurement target point 12 is a failure point such as a disconnection defect, the voltage v2 should not be observed, but an error voltage as shown by Ve in FIG. 1 is detected. especially,
The switching period T of the measurement target point by the multiplexer is 1.
If the test speed is increased to 0m5 or less, the input bus 1 between the multiplexer and the A-D converter in Figure 3
The residual voltage ν accumulated in the stray capacitance C to ground existing at 0
e (residual voltage at the previous measurement target point 11 indicated by the dotted line) is observed.

In this case, if the measured voltages, for example, vl and v2, are values that are close to each other, it is necessary to measure the DC voltage with a high-precision A-D converter, and the input bus 10 in FIG. The existing stray capacitance poses a major hindrance to improving measurement accuracy.

[Means for solving problems]

FIG. 1 is a block circuit diagram of an embodiment of the voltage measurement error prevention circuit of the present invention. In the figure, measurement target points 11, 12 of the test object. -1n DC voltage is sequentially switched by the multiplexer MPX, and when this is A-RO converted to measure the voltage, the residual voltage remaining on the input bus 10 connected to the A-D converter is transferred to the multiplexer MPX.
Relay contact r that operates at the same cycle as the switching cycle gT of X
s and a resistor R having a lower value than the impedance Zin between the input terminal 9 of the A-D converter and the ground 8 are removed by a discharge circuit 7 connected in series. The above problem has been solved as a circuit.

[Effect]

In the present invention, a discharge circuit consisting of a relay contact rs and a resistor R is inserted between the input bus 10 and the ground 8, directly connected to the input terminal of the A-D converter of the voltage measurement circuit, and the above-mentioned By turning on the relay contact rs, the residual voltage present in the input bus from the previous measurement is once cleared to zero, thereby ensuring the initial setting of the measurement.

Therefore, by performing this initial setting each time in conjunction with the switch operation of the multiplexer that sequentially performs voltage measurements at multiple points, a stable voltage measurement circuit without measurement errors can be realized.

〔Example〕

Regarding the following nine embodiments of the voltage measurement error prevention circuit of the present invention,
A detailed explanation will be given according to the time charts of the embodiment circuit of FIG. 1 and the voltage measuring circuit of FIG. 2.

In the circuit block diagram of the embodiment, the same symbols and reference numbers are given to functional circuit parts that are the same as those in the prior art, so that the main parts of the present invention can be clearly understood.

In the circuit block diagram, 7 is a discharge circuit that forms the essential part of the present invention.

The discharge circuit 7 is connected to an input bus 10 connecting the multiplexer MPX to the DC voltage measuring device DCM.

Close to the input terminal 9 of the A-D converter of the bus,
A circuit in which a resistor R and a relay contact rs are connected in series is connected to the bus bar 10.
It is inserted between the ground and the ground.

Furthermore, an equivalent stray capacitance C proportional to the input bus length exists between the measurement input bus 10 and the ground 8, and the discharge circuit 7 is inserted in parallel with the capacitance C.

It is necessary that the resistance R of the circuit 7 is sufficiently smaller than the impedance Zin between the input terminal 9 of the ^-D converter and the ground. The rs connected in series with this does not need to be limited to a relay contact; it is an analog switch (semiconductor switch element) that can operate at high speed and is easy to pulse drive.
But it doesn't matter.

The operation of such relay contact rs or switch element causes input mother! 'The residual charge of the capacitor C accumulated or remaining in iIO can be quickly removed.

The operation of the embodiment circuit shown in FIG. 1 and the operation method of the relay contact rs will be explained with reference to the time chart shown in FIG.

As is clear from comparison with FIG. 4, FIG. 2 is an example in which the voltage V at the measurement target point 11 and the voltage V2 at the measurement target point 12 are measured according to the operation of the switches Rsl and Rs2 by the MP. shown.

Drive pulse I of 9 periods T before or after voltage measurement
's (three pulses are shown in the figure) is the relay contact r
s, thereby turning on the contact rs and A-
The voltage at the input terminal 9 of the D converter is once set to zero. Thereafter, the voltage v1 at the measurement target point 11 is input to the AD converter. Even when the voltage v2 of the next measurement target point 12 is input to the A-D converter, before measuring the voltage V2, the contact rs is turned on by the drive pulse Ps, the residual voltage of the voltage v11 measurement is cleared, and the voltage is temporarily reset. It is set to zero state, and then the DC voltage is taken into the DC voltage measuring device DCM.

That is, the multiplexer switches Rsl, Rs□-
・.

By operating the relay contact rs of the discharge circuit 7 in conjunction with the switching operation of Rsn, the residual charge due to the stray capacitance of the input bus 10 is cleared. However, the relay contact rs turns off the relay contact rs of the discharge circuit 7 during the TI period of measuring the voltage v1 at the measurement target point, and during the T2 period of measuring the voltage v2 following this.

Although the above-mentioned embodiment cites the case where the measurement target point, which is the test object, is a printed circuit board assembly, the voltage measurement error prevention circuit of the present invention is not limited to this.

For example, it is effective when applied to a wide range of tests in which the operating voltages of a large number of electronic components are checked simultaneously using an A-D converter having a high resistance input impedance.

〔Effect of the invention〕

According to the voltage measurement error prevention circuit of the present invention explained above,
This method has the remarkable effect of increasing the reliability of DC voltage measurement and quickly testing printed circuit board circuits and the like under operating conditions that have multiple checkpoints.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the voltage measurement error prevention circuit of the present invention. FIG. 2 is an operation time chart of the discharge prevention circuit shown in FIG. 1. FIG. 3 is a block diagram of a conventional voltage measurement circuit. Figure 4 is a time chart during voltage measurement. In the figure, 7 is a discharge circuit of the present invention. 9 is the input terminal of the ^-D converter. 10 is a measurement input bus (input bus 'fa). LL 12.13. ..., n is the measurement target point. MPX is a multiplexer. Until now, Meiden Co., Ltd. has been a professional in the series of
・Tsuku diagram No. 1 Diagram L's voltage, 8"l'r law hard power pro., Fb] No. 3
Figure Voltage 11° % Mukhyahi No. 48

Claims (1)

[Claims] In order to sequentially switch the DC voltage of the test object using a multiplexer and input it to an A-D converter to measure the voltage at a large number of measurement points, the input circuit of the A-D converter consists of a switching element and a resistor. A voltage measurement error prevention circuit characterized in that a discharge circuit is provided, and residual charge in an input circuit is removed by closing a switching element at the same cycle as a switching cycle of a multiplexer before voltage measurement.