JPS61105470A - Control system for decision making of insulation resistance - Google Patents

Abstract

PURPOSE:To eliminate the influence of the absorbed current of a connection cable and a changing current and the leak current of a stray capacitance by providing measurement terminals, resistances, amplifiers, an adder, resistance decision output signal line, etc., and detecting the absorbed current, charging current, and leak current. CONSTITUTION:The amplifiers 1 and 2, current detection resistances 3 and 4, adder 6, measurement terminals 16 and 17, and resistance decision output signal line 24, etc., are provided. Then, the output of the amplifier 1 and the output of the amplifier 2 are opposite in phase as to a current flowing through a printed board, and the output part of the adder 6 generates no output as to the current flowing through the printed board. Further, a signal corresponding to the unbalance between currents at a voltage application side and an earth side appear at the output. A comparator 22, on the other hand, outputs logic 0 when the insulation resistance 18 is larger than a specific value and logic 1 when not. An inhibition gate 23 is opened when the output 14 of an OR gate 13 is 0 to send the output of the comparator 22 to the resistance decision output line 24. Thus, an accurate measurement is taken.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an insulation resistance determination control method, and particularly to an insulation resistance determination control method in a test device that measures the insulation resistance between spaced conductors on a printed circuit board, for example. Regarding.

[Conventional technology]

For example, when measuring the insulation between conductors of a printed circuit board using the voltammeter method, the following points need to be kept in mind.

(al) A scanner, mounting jig, etc. are inevitably interposed between the sensor (measuring unit) of the tester and the printed board, and these have leakage current and stray capacitance.

(bl) It is necessary to distinguish between the current flowing through them and the leakage current of the original printed circuit board.

To solve these problems, generally, the gradient of change in the voltage applied to the measurement line is detected, and when the gradient disappears, charging is determined to be complete, and subsequent determination results are valid. . A differential circuit is used to detect the slope.

[Problems to be solved by the invention] When detecting the gradient of voltage, the gradient is obtained by differentiating the voltage, but in the case of a pure CR circuit, the charge/discharge characteristics are closely related between voltage and current. , and V = E・(1-e
The relationship xp (-t/cg)) holds true,
When the change in voltage falls below a certain value, the current value also falls below, and the purpose can be achieved.

However, in the case of an actual system, there is an absorption current or leakage current that continues to flow even after the voltage has stabilized as a current flowing through the capacitance of a cable or the like.

In this case, the absence of a voltage gradient does not correspond to the absence of current flow.

As a result, accurate measurements cannot be made. This correspondence relationship is shown in FIG.

FIG. 5(L) is a diagram showing changes in applied voltage;
FIG. 5(2) is a diagram showing changes in charging current.

In Figure 5 (2), ■ indicates the original charging current, and ■
indicates the value obtained by adding the absorbed current to the original charging current.

Therefore, it is desired to solve the problems of the conventional method and enable accurate measurement.

[Means for solving problems]

In order to solve the above problems, the present invention provides first and second measurement terminals that are connected to insulation resistance measurement terminals of a test object, and a measuring power source that applies a voltage for measuring insulation resistance to an object;
a first resistor having one end connected to the measurement terminal and the other end connected to the measurement power supply; and a second resistor having one end connected to the second measurement terminal and the other end connected to the measurement power supply. a resistor; a first amplifier connected to both ends of the first resistor to detect the voltage across the resistor; and a first amplifier connected to both ends of the second resistor to detect the voltage across the resistor. a second amplifier that detects the voltage in the opposite direction to the input voltage to the amplifier; a voltage adding circuit that adds the output of the first amplifier and the output of the second amplifier; and the voltage adding circuit of the voltage adding circuit. Voltage gradient determination means for detecting the slope of the output voltage and determining that the slope is below a certain value; and detecting the absolute value of the output voltage of the voltage adding circuit and determining that the absolute value is below the certain value. and insulation resistance determination control signal generating means for generating an insulation resistance determination control signal for instructing whether insulation resistance can be measured based on the output of the voltage gradient determining means and the output of the voltage absolute value determining means. It is characterized by having a small amount of insulation resistance and controlling the determination of insulation resistance.

[For production]

The present invention provides: (a) a circuit configuration that detects when the current component flowing through the connection cable becomes less than a predetermined value; (Ll) a change (gradient) in the current component flowing through the connection cable;
A circuit configuration that detects when the current component that flows through the connecting cable becomes less than a predetermined value, and when the change (gradient) of the current component becomes less than a predetermined value, it is determined that charging is complete. It has a circuit configuration and provides timing that allows accurate measurement of insulation resistance.

〔Example〕

FIG. 1 is a circuit configuration diagram of one embodiment according to the present invention, in which 1 and 2 are amplifiers, 3 and 4 are current detection resistors, 5 is a measurement power supply, 6 is an adder, 7 is a subtracter, 8 is a differentiation circuit, 9 and 10 are absolute value amplification circuits, 11 and 12 are comparators, 13 is an OR gate, 14 is a prohibition output signal (line), 15 is a measurement output signal (line), 16 and 17 are measurement terminals, 18 is the resistance to be measured (insulation resistance), 19 and 20 are the cable capacitances, 21 is the stray capacitance of the resistance to be measured, 22 is the comparator, 23 is the inhibition gate, 2
4 is a resistance measurement output signal (line).

In the figure, the left side of the broken line passing through measurement terminals 16 and 17 has a capacitance C.
L, 21 is the capacity of the printed board. Resistor 3 and amplifier 1
constitutes a current-voltage conversion amplifier on the voltage application side, and the gain is G
It is.

The resistor 4 and the amplifier 2 constitute a ground-side current-voltage conversion amplifier, and the gain is G. The currents flowing through the resistors 3 and 4 have opposite polarities.

Therefore, if the cable capacitances 19 and 20 do not exist, the output current of the measurement power supply 5, which is the voltage application source, will pass through the path of the resistor 3, the resistor to be measured 18, and the resistor 4, and the current will flow through the resistor 3. The current flowing through resistor 4 is the same. Furthermore, the output of amplifier 1 and the output of multiplier 2 are in opposite phase with respect to the current flowing to the printed board, and at the output section of adder 6, the current flowing to the printed board is equal to the unbalanced output current. appears.

Conversely, the current flowing through the printed circuit board is added to the output of the subtractor 7 to obtain twice the current output.

Parts numbered 8 to 14 are unbalanced portions (cable capacity, leakage)
The differential circuit 8 uses a CR time constant, and the absolute value amplification circuit 9-10 creates a positive output voltage proportional to the input, whether positive or negative. The comparators 11 and 12 are circuits that have a judgment function that compares analog voltages with a certain value and converts them into logic signals.If the input voltage exceeds a certain value (in this case, the comparator 12 , charging current limit value, comparator 1
2 is a limit value for the change in charging current) that creates a positive logic output, and the OR gate 13 is an OR circuit.

In this way, the absolute value amplifying circuit 10 and the comparator 12 detect the current component flowing through the connecting cable, and the differentiating circuit 8, the absolute value amplifying circuit 9, and the comparator 11 detect changes in the current component flowing through the connecting cable.

Further, the output of the subtracter 7, which is a voltage proportional to the current flowing through the insulation resistor 18, is determined by the comparator 22 as to whether it is a predetermined value set in advance or not. The comparator 22 is configured to output logic "0" when the insulation resistance 18 is greater than a predetermined value, and output logic "1" when it is less than a predetermined value, for example. Next, the inhibition gate 23 is activated when the output 14 of the OR gate 13 becomes "0" (that is, when there is a leakage, the charging current is below a predetermined value, and the change component of the charging current is also below a predetermined value). ) is set in the open state and sends the output of the comparator 22 onto the resistance determination output signal line 24.

A control section (not shown) monitors the state of the output of the inhibit gate 23 (resistance judgment output signal line 24) when the output of the OR gate 13 (signal line 14) is "O", and if it is in the "0" state, the insulation The resistance was large enough and the insulation was judged to be good, and conversely, “
1”, it is determined that the insulation is defective.

Furthermore, the value of the insulation resistance 18 is the same as that of the OR gate 1.
It can be determined by determining the voltage value of the output of the subtracter 7 (measurement output signal line 15) when the output of the subtractor 7 (signal line 14) is "0" and multiplying it by a predetermined coefficient.

This predetermined coefficient is determined by the gain of the amplifier 31.2, the resistance value of the resistor 3.4, etc.

Next, we will explain the equivalents to make the operation of each part clearer.

When the impedance of each element is expressed using S, Zr2
-zt4-> = (1)+ (2)= (R
+ r )(1+5-CL -r) ・(l+S
-Csu・RA)□(3) 2194t4・λo・+q=(R+r)(1+Sr5
) ・ (1+5rae)□(4) ZIs-'2J・U4-1'? -21F (R+
2 r )(1+Sτ7 )・(1+Sτ? )
(1+SτS)・(1+Sr&,)□(5) However, τ1=CL+・r τz=C ・RX r4 =Cp−(RX +r) τra +τb =τ1 +τ21−τushiτ5 Φ τet al. =τL' τλ +τ3 ・τ4+ □ ・ (
T5+T et al.) R+2r The current flowing through the resistor 3 is the applied voltage, which is a step voltage with amplitude E, so it is
・(1+S・τ7)・(1+S・1g)□(6) The current ■4 flowing through the resistor 4 can be found by the following procedure.

Rz+'lr S ・ (1+Srwa) ・ (1+Sr8
)□(7) ■19・λ1 = ■4・20”119・nido4−・2
riS (1+Sr7) ・(1+Sτg)□(8
) 13 and ■Φ are each converted into voltage and amplified by a resistor r of 3.4. When the gain in the term is G, (1+Sτri) (1+Sτb) S (1+SτI?) (1+Sτ9) □ (9) S・ (1+Sτ7)・ (1+S = 9) The difference component is
Signals are added at V3 - V4, and the sum component is V3+
The charging current is canceled at V4.

S・ (1+S = 7)・ (1+SτB)−□ (11
) (1+-3τ7)・(1+Sτ9) However, τ9 ・τW= τs Iτ&/2 τ? +τto”<τλ +τζ +τ et al.)/2K
-τS + τmu τ2 τ11 ” τta °τb / (τ5 + mu τ2) When converting V3 +V4 into time, as derived from equation (13), the steady current component flowing through Rx does not enter into this.

Also, depending on the relationship between time constant τ9, and τ7, between 1=0 and t=ω when voltage is applied, equation (13) (%) may change from a positive value to a negative value, or It can change from a negative value to a positive value.

In an insulation tester for printed circuit boards, etc., it is natural that no charging current should flow in order to give a good judgment, but it is no good even if a negative current (apparently) flows; It is necessary that it does not flow.

Therefore, the sum component of equation (13) cannot be used as a judgment prohibition signal as it is, and first, an absolute value circuit is used to make it a positive signal whether it is a positive voltage or a negative voltage. . This can simply be a double-wave rectifier circuit,
In reality, it is constructed by inserting a detection diode into a feedback multiplier.

Next, even when using this absolute value circuit, in the case of a signal that crosses 0 over time (for example, as shown in Fig. 2 (1)), in order to prevent erroneously determining that charging has ended at the cross point, Using the differential value of equation (13), the determination is waited until the differential value becomes 0. This differential value is used to determine whether or not there is a change in the charging current, and there can be either a positive change or a negative change.

The differential value may also be positive or negative. Therefore,
The differential value also uses an absolute value circuit.

By converting the presence or absence of the absolute value of the charging current obtained above and the presence or absence of a change in the charging current into logic levels, and taking the logical sum, a reliable judgment prohibition circuit can be constructed.

FIG. 3 illustrates one embodiment of the present invention side by side with a printed board-to-be-measured uniformity measuring device.

In the figure, the measuring device is on the right side of the broken line passing through numbers 16 and 17, which is the same as the one shown in FIG. 25 and a connecting cable.

In the example of FIG. 3, 19', 20', and 26 are the stray capacitances of each cable, and this value is particularly the second.

Furthermore, in the case of a printed circuit board testing device, the number of connected circuits may exceed several thousand and even reach tens of thousands.

Also, the capacitance seen from the measuring instrument side is the capacitance on the application side (this is C
p), the dimension I seen from the ground side (this is taken as C)
, Furthermore, there is no regularity in the magnitude relationship between the capacitance between the application side and the ground side (this is referred to as Cc), and the capacitance C
A large imbalance may occur between L, CC, and Cp. In the presence of such an imbalance, conventional methods are likely to initiate measurements and produce erroneous results.

In addition, in the case of a general connection cable, an absorption current flows,
According to the conventional method of differentiating the applied voltage, the absorbed current (
) of the cable.

FIG. 4 shows an example of absorbed current.

Figure 4 (al is one with relatively small capacity, Figure 4 (b)
1 has a large capacity, and these are approximately 20 in Figure 4 (a).
0 (l p F) Figure 4(b) shows an example of a value of approximately 0.15 μF.As can be seen from the data, when the time is close to 0, the main charging current is the capacitor, but when the charging is finished, After that, a current flows that decreases over time.On the other hand, the applied voltage does not change because charging has already been completed.

Therefore, conventional methods cannot distinguish between the insulation resistance of the printed board and the absorbed current of the cable.

The present invention detects the current component flowing in the connecting cable and its change, and does not perform any measurement during this time, so the cable current is excluded from the measurement results.

〔effect〕

According to the present invention, when measuring the insulation resistance between conductor patterns on a printed circuit board, (a) detecting the absorption current of the connection cable, the charging current of the stray capacitance, and the leakage current;
(b) It is possible to detect the transient state of the circuit and eliminate its influence; (c) It is possible to perform measurements regardless of the ratio of stray capacitance of each measurement line. .

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of one embodiment of the present invention, and FIG. 2 (
a) is a diagram showing an equivalent circuit of the measurement system, FIG. 2 (bl is a diagram showing an example of a composite waveform of the sum of measured currents (voltages), and FIG. FIG. 0 and FIG. 4, which show an example of a switching device and a regulator, are diagrams showing an example of the absorbed current, and FIG. 5 is a diagram showing the relationship between the applied voltage and the absorbed current. In FIG. 1, l and 2 are Amplifier, 3 and 4 are resistors for current detection, 5 is a power supply for measurement, 6 is an adder, 7 is a subtracter, 8 is a differentiation circuit, 9 and 10 are absolute value amplification circuits, 11 and 12 are comparators, 13 is OR gate, 14 is a prohibition output signal (line),
15 is the measurement output signal (line), 16 and 17 are the measurement terminals, 1
8 is the resistance to be measured (insulation resistance), 19 and 20 are the cable capacitances, 21 is the stray capacitance of the resistance to be measured, 22 is the comparator, 23 is the inhibition gate, and 24 is the resistance judgment output signal (line).
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10(hs3(a +
141110 S ID0y+5
? lJOmS 3θ0-5(b)
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Claims (2)

[Claims] (1) The first terminal connected to the insulation resistance measurement terminal of the test object.
and a second measurement terminal, a measurement power supply that applies an insulation resistance measurement voltage to the test object via the first and second measurement terminals, one end of which is connected to the first measurement terminal and the other end of which is connected to the first measurement terminal. a first resistor connected to the measurement power supply; and a second resistor connected to the measurement power supply.
a second resistor having one end connected to the measurement terminal and the other end connected to the measurement power source; a first amplifier connected to both ends of the first resistor and detecting the voltage across the resistor; a second amplifier connected to both ends of the second resistor to detect the voltage across the resistor in a direction opposite to the input voltage to the first amplifier; and an output of the first amplifier. and the output of the second amplifier, a voltage gradient determining means for detecting the slope of the output voltage of the voltage adding circuit and determining that the slope is below a certain value, and the voltage adding circuit. Voltage absolute value determining means for detecting the absolute value of the output voltage of the circuit and determining that the absolute value is below a certain value; and insulation resistance based on the output of the voltage gradient determining means and the output of the voltage absolute value determining means. 1. An insulation resistance determination control method comprising at least an insulation resistance determination control signal generating means for generating an insulation resistance determination control signal for instructing whether or not measurement is possible. (2) A voltage subtraction circuit that creates a voltage difference between the output of the first amplifier and the output of the second amplifier, and a voltage subtraction circuit that detects the absolute value of the output voltage of the voltage subtraction circuit, and the absolute value is below a certain value. and a determination output means that outputs an insulation resistance quality determination signal based on the determination signal and the insulation resistance determination control signal. Claim No. (1)
Insulation resistance judgment control method described in section.