JPH09297165A - Battery tester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge the cause of overflow of an A/D converter by comparing the output voltage of an ac constant power source with a standard value, and detecting the close and open of a current path for connecting the constant power source to a battery according to whether the output voltage exceeds the standard value or not. SOLUTION: The output voltage Vo of an amplifier 1 is full wave rectified and smoothed to form a dc voltage 2 Vo/π, which is then compared with a threshold voltage VH. When it is less than the voltage VH, the output of a comparator 2 becomes about a positive power source voltage +Vcc to generate a voltage +Vcc in a load resistance 7. An inverter 3 receives it and transmits a signal of level L to a CPU 14. The CPU 14 judges the absence of disconnection between a current source 8 and a battery 11 even when the data from an A/D converter 13 overflows, and displays a range switching. When a disconnection is present, the smoothed dc voltage is about 2Vcc/π, the output of the comparator is zero, and the inverter 3 transmits a signal of level H to the CPU 14. The CPU 14 then judges a disconnection and displays it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery tester, and more specifically, when measuring internal resistance of a battery (battery) which is an object to be measured, its battery terminal and a measuring probe are reliably connected. It is related to the technology to determine whether or not.

[0002]

2. Description of the Related Art In general, the deterioration state of a battery (primary battery, secondary battery) is determined by its internal resistance (equivalent series resistance) and its terminal voltage. That is, as the deterioration progresses, the internal resistance tends to increase and the terminal voltage tends to decrease.

Referring to FIG. 7, for example, a case of measuring the internal resistance of a vehicle-mounted battery will be described. A pair of source side probes 9 drawn from an AC constant current source 16 will be described.
a and 9b and a pair of sense-side probes 10a and 10b from the measuring unit 15 are connected to the + terminal and − of the battery 11, respectively.
An AC constant current for measurement is made to flow from the AC constant current source 16 in contact with the terminals, and the AC voltage generated between the terminals is measured by the AC voltmeter 12 of the measuring unit 15.

This measured value is obtained by the A / D converter 13 in the next stage.
Is converted into digital data by the CPU 14 and converted into a resistance value by the CPU 14. However, when the internal resistance Rs increases due to deterioration of the battery 11 or the like, the voltage generated between both terminals also increases in proportion to it. When the measurable rated value is exceeded, the A / D converter 13 overflows.

Thus, in principle, the battery 11 +
A pair of probes 9a, 9 on the source side are connected to the terminal and the-terminal.
Although a total of four probes of b and a pair of probes 10a and 10b on the sense side are brought into contact with each other, if each of the probes is brought into contact with the terminal separately, the work is troublesome.

Therefore, in practice, one probe 9a on the source side and one probe 10a on the sense side are
The other probe 9b on the source side and the other probe 10b on the sense side are commonly connected to, for example, a clip-type positive side clamp probe and a negative side clamp probe, respectively. The positive and negative terminals of one battery 11 are brought into contact with each other.

[0007]

However, when such a clamp probe is used as two terminals, there is a poor contact between the clamp probe and the battery terminal, for example, when the clamp probe is disconnected from the battery terminal. Since the AC constant current source 16 has no load and the output voltage thereof is directly applied to the AC voltmeter 12, the A / D converter 13 causes overflow in the same manner as above.

Therefore, when the A / D converter 13 overflows in this way, conventionally, the cause may be the increase in the internal resistance Rs of the battery 11, or the contact failure (disconnection) of the clamp probe to the battery terminal. There was a problem that it was not possible to tell if it was due to.

The four probes 9a, 9b; 10
As shown in FIG. 7, four probes 9a, 9b; 1 are used without substituting the two clamp probes for a and 10b.
When 0a and 10b are directly used as the four terminals, a resistance element having a high resistance value may be connected between them to prevent the probe 9a and the probe 10a from being opened. Even in this case, if there is a contact failure that is considered as a disconnection between the probe and the battery terminal, the A / D converter 13 overflows as in the above case.

The present invention has been made to solve the above-mentioned problems, and an object thereof is that the overflow of the A / D converter causes a disconnection of the current path between the probe and the battery terminal (hereinafter referred to as "disconnection"). Another object of the present invention is to provide a battery tester capable of determining whether it is due to the increase in internal resistance due to deterioration of the battery.

[0011]

In order to achieve the above-mentioned object, according to the present invention, an alternating current for measurement is made to flow from an alternating constant current source to a battery to be measured and is generated between terminals of the battery at the measuring section side. In a battery tester that detects an AC voltage and converts the AC voltage into a resistance value to measure the internal resistance of the battery,
The output voltage from the AC constant current source is compared with a predetermined reference value, and the current path between the AC constant current source and the battery is closed or open depending on whether or not the reference value is exceeded. It is characterized by having a disconnection detection circuit for detecting whether or not

In this case, the AC constant current source amplifies a constant level AC voltage generated from the AC constant voltage source with an amplifier, and a resistor provided in a current path from the output side of the amplifier to the battery causes It is configured to set a measuring AC current flowing through the battery to a predetermined level. The resistance provided in the current path of the AC constant current source is preferably such that its resistance value can be switched in a plurality of stages at a predetermined magnification.

The disconnection detection circuit includes a rectifying / smoothing circuit for converting the amplified voltage of the amplifier into a DC voltage, and a voltage comparing circuit for comparing the DC voltage formed by the rectifying / smoothing circuit with a predetermined threshold value. And a logic signal generation circuit that converts the comparison output of the voltage comparison circuit into a voltage signal of logic level L or H and outputs the voltage signal to the measurement unit. When the logic signal is in a predetermined level state, the measurement unit described above It is determined that the current path from the AC constant current source to the battery is in a disconnection state including poor contact.

In the present invention, the voltage comparison circuit of the disconnection detection circuit includes an amplifier to which the DC voltage formed by the rectifying / smoothing circuit is applied to its-input terminal.
A reference voltage obtained by dividing the power supply voltage of the tester to a predetermined level and a voltage obtained by dividing the output voltage of the amplifier by 1 / n (n is an arbitrary voltage division ratio) are applied to the input terminal. It operates as a hysteresis comparator in which the threshold voltage of the + input terminal is switched between high and low depending on the presence or absence of an output voltage.

The logic signal of a predetermined level output from the disconnection detection circuit to the measuring section at the time of disconnection is generated when the resistance of the measuring current path including the internal resistance of the battery is larger than the value shown in the following equation. Rs = {(π · VH / 2Vi) −1} × R12 Rs: Resistance of measurement current path including internal resistance of secondary battery R12: Measurement current setting resistance in AC current source VH: High potential threshold of hysteresis comparator Voltage Vi: AC constant voltage source voltage in the AC constant current source

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the outline of the configuration of a battery tester to which the present invention is applied. That is, this battery tester includes a disconnection detection circuit 4, an AC constant current source 8, an AC voltmeter 12 similar to the conventional device, and an A / D converter 1.
3 and a measuring unit 15 having a CPU 14.

The AC constant current source 8 receives, for example, a constant level AC sine wave voltage generated from the AC constant voltage source 5, and forms two constant AC sine wave currents for measurement.
And resistors R8 to R13. This measuring AC current is supplied to the battery 11 via the probes 9a and 9b, and the AC voltage generated between the two terminals of the battery is measured by the AC voltmeter 12 by the probes 10a and 10b.
Is taken into. Thereafter, the internal resistance Rs of the battery 11 is measured as in the case of the conventional device.

Now, assuming that the resistance values of the above four resistors R8 to R11 are set equal to each other, that is, R8 = R9 = R10 = R11, the amplifier 6 is connected to the + input terminal side (i). It becomes a non-inverting amplifier with an amplification factor of 2 with respect to the applied voltage. In this case, the voltage applied to the + input terminal of the amplifier 6 is the sum of the output of the AC constant voltage source 5 and the output of the amplifier 7.

Here, the resistance R1 on the + input terminal side of the amplifier 7
3 is set to a value sufficiently larger than the resistance R12 on the output terminal side (e) of the amplifier 6 and the internal resistance Rs of the battery 11, the measuring AC constant current I sent from the amplifier 6
Flows through the resistor R12 to the resistor Rs.

Therefore, the voltage generated between both terminals of the battery 11, that is, the voltage I × Rs generated between the (nu) side and the ground is applied to the + input terminal of the amplifier 7 without being attenuated. Since the amplifier 7 has a very high input impedance and is a voltage follower amplifier with an amplification factor of 1, which can be regarded as zero, a voltage I × Rs equal to the input voltage appears on the output terminal side (Le).

Therefore, the output voltage component of the AC constant voltage source 5 applied to the + input terminal (ri) side of the amplifier 6 is Vi {R11 / (R9 + R11)} = Vi / when the (le) side is regarded as the ground potential. 2 ......... (1). Further, the output voltage component of the amplifier 7 applied to the same (i) side is I · Rs {R9 / (R9 + R11)} = I · Rs / 2 when the output impedance of the AC constant voltage source 5 is regarded as zero. (2)

The + input terminal voltage of the amplifier 6 is obtained by adding the equations (1) and (2) by the principle of superposition. That is, Vi / 2 + I · Rs / 2 = (Vi + I · Rs) / 2. Since the amplifier 6 amplifies this input voltage with an amplification factor of 2, if the output voltage on the (e) side is Vo, then Vo = Vi + IRs (3)

On the other hand, since the output voltage Vo is Vo = I (R12 + Rs) (4), from the above equation and the equation (3), Vi + I.Rs = I.R12 + I.Rs I · R12 Therefore, I = Vi / R12 (5) By substituting the equation (5) into the equation (4), the output voltage Vo of the amplifier 6 is Vo = Vi (R12 + Rs) / R12 (6).

According to the equation (5), since the generated voltage Vi of the AC constant voltage source 5 is constant, the measuring current I flowing in the battery 11 can be set to an arbitrary value by the value of the resistor R12. Therefore, in this device, the value of the internal resistance Rs is not uniform due to the degree of deterioration of the battery, and the value of the resistance R12 is switched in a plurality of stages (not shown).

Now, in a certain range, the current I is supplied to the battery 11
, The terminal voltage I × Rs of the battery is A / D
If the maximum measurable level (rated value) of the converter 13 is exceeded, all bits of the digital conversion data are fixed to 1 and a so-called overflow state occurs. In this case, the range of the resistor R12 is switched to the high resistance side until the overflow disappears, and the measurement current I
Lower the value of.

A probe 9a or 9 on the side of the AC constant current source 8
If b or both of them have a poor contact with the terminal of the battery 11, the measurement current I does not flow in the battery, which causes a disconnection, and the AC constant current source 8 is opened between the probes 9a and 9b. The voltage appears. When this open circuit voltage is taken into the AC voltmeter 12 via the probes 10a and 10b, the A / D converter 13 causes overflow in the same manner as described above.

In this case, the open circuit voltage is almost up to the power supply voltage of the device, and the measuring current does not flow.
The overflow phenomenon cannot be solved by setting the value of to any range. However, since such range operation is troublesome, the output voltage of the AC constant current source 8 is monitored by the disconnection detection circuit 4, and the presence or absence of disconnection in the measurement current path is automatically determined.

The disconnection detection circuit 4 includes, for example, an amplifier 1, a transistor Tr, a full-wave rectification unit including resistors R1 and R2, a smoothing unit including a resistor R3 and a capacitor C, a comparator 2, and resistors R4, R5, and R6. It is composed of a voltage comparison unit provided and a logic signal output unit provided with a diode D, a resistor R7 and an inverter 3.

Now, the measuring current I sent from the AC constant current source 8 normally flows from the probe 9a through the battery 11 and the probe 9b, and the voltage generated in the internal resistance Rs is AC through the probes 10a and 10b. It is assumed that the voltage is taken in by the voltmeter 12. In this case, the output voltage Vo of the amplifier 6 in the AC constant current source 8 is also applied to the + input terminal of the amplifier 1 provided in the disconnection detection circuit 4. This input voltage is shown in FIG. 2A, and the operation of each part of the disconnection detection circuit 4 will be described below with reference to FIG.

When the amplifier 1 and the transistor Tr are in the active state, the amplifier 1 has a voltage at its-input terminal, that is, the emitter voltage of the transistor Tr (FIG. 2C).
Outputs an output (FIG. 2B) to control the transistor Tr so that it has the same potential as the voltage Vo applied to the + input terminal of the amplifier 1.

For example, if the voltage Vo applied to the + input terminal of the amplifier 1 swings to the negative side during the period of 0 to π, the amplifier 1 emits a negative voltage to reduce the emitter current of the transistor Tr. As a result, the voltage drop of the resistor R2 is reduced, the emitter voltage of the transistor Tr approaches the negative power supply voltage −Vcc direction, and the − input terminal of the amplifier 1 has the same potential as the negative voltage Vo applied to the + input terminal. . When the voltage Vo applied to the + input terminal exceeds the negative minimum level and rises toward the zero level, the amplifier 1 controls the transistor Tr so that the emitter current increases contrary to the above.

Since the base current supplied from the amplifier 1 to the transistor Tr is small during the period of 0 to π, it can be considered that the emitter current and the collector current are equal to each other. Therefore, when the emitter current decreases, the voltage drop of the resistor R1 decreases, and the collector voltage of the transistor Tr increases in the positive power supply voltage + Vcc direction. Here, if the resistance R1 is set to the same value as the resistance R2, the voltage drop widths of both resistances become equal, so that the transistor Tr
A voltage (FIG. 2D) obtained by inverting the above-mentioned emitter voltage (FIG. 2C) to the positive side appears in the collector of.

Next, in the period from π to 2π, when a positive voltage Vo (FIG. 2A) is applied to the + input terminal of the amplifier 1, the amplifier 1 has a positive voltage (FIG. 2) to the base of the transistor Tr. (B)) to increase its emitter current,
The voltage drop across the resistor R2 is increased so that the voltage applied to the-input terminal (Fig. 2C) becomes the same potential as the positive voltage Vo applied to the + input terminal.

In this case, on the collector side, if an attempt is made to pass a current commensurate with the emitter current, the collector voltage will decrease due to the increased voltage drop of the resistor R1 and will coincide with the base voltage rising to the positive side. , The collector current cannot be increased. Rather, the collector voltage has almost the same potential as the base voltage and rises toward the power supply voltage + Vcc so as to be pushed up to the base voltage. This allows
The voltage drop across the resistor R1 is forcibly reduced, and the collector current also decreases accordingly.

When the input voltage Vo passes the maximum level on the positive side and drops toward the zero level, the base voltage and the emitter voltage of the transistor Tr start to drop, and the potential difference between the collector and the power supply voltage + Vcc increases. As a result, the collector current starts to increase, and as the voltage drop across the resistor R1 increases, the collector voltage drops toward the zero level while following the base voltage.

Therefore, the waveform of the collector voltage between π and 2π is almost the same as that between 0 and π (see FIG. 2).
(D)), a full-wave rectified voltage can be obtained. Note that this π
In the period of up to 2π, the emitter current becomes larger than the collector current, but the current corresponding to the difference is supplied from the amplifier 1 to the emitter side via the base.

The above is an example of the full-wave rectification circuit using the amplifier and the transistor, but it is also possible to use a full-wave rectification circuit of the absolute value detection waveform using the amplifier and the diode. However, since the purpose here is not to measure the absolute value, the above circuit is sufficient in terms of performance.

The full-wave rectified voltage generated at the collector of the transistor Tr has its pulsating component removed in the smoothing section having a low-pass filter composed of the resistor R3 and the capacitor C, and becomes a DC voltage, which is supplied to the comparator 2 of the voltage comparing section. (Fig. 2 (e)). When the maximum amplitude of the AC voltage input to the amplifier 1 is Vo, the smoothed DC voltage has a magnitude of (2 / π) Vo.

The + input terminal of the comparator 2 has an R when the positive power source voltage + Vcc is divided by the resistors R4 and R5.
The voltage on the fourth side is given as the reference voltage Vref.
That is, from the positive power supply voltage + Vcc to the resistance R4 and the resistance R4.
When the current flowing through 5 to the ground side is I1, I1 = Vcc / (R4 + R5) (7) and the voltage drop generated by this current flowing through the resistor R5 is the reference voltage Vref. Vref = I1.R5 (8) = Vcc.R5 (R4 + R5) (9) This reference voltage Vref is shown by a solid line in FIG.

In the figure, if the minus input terminal of the comparator 2 has no signal and is at zero level before the time t1, its output terminal voltage is substantially positive power supply voltage + Vcc.
The current flows from the output terminal to the ground side through the resistors R6 and R5 (Fig. (F)). This current is I2
Then, I2 = Vcc / (R5 + R6) (10), and the two currents I1 and I2 flow together in the resistor R5.

Therefore, the resistance R is increased by the two currents that have merged.
VH = (I1 + I2) R5 ... (11) Substituting equation (8) and equation (10) into the above equation, VH = Vref + Vcc.R5 / (R5 + R6). … (12) The second term in the above equation is that the positive power supply voltage + Vcc is the resistance R
This corresponds to the voltage divided by 5 and R6. The voltage obtained by adding the divided voltage to the reference voltage Vref becomes VH, which is shown by the broken line in FIG.

Here, for example, at time t1, the negative input A of the comparator 2 is lower than the reference voltage Vref.
Even if the voltage of V is applied or the voltage of the level B higher than the reference voltage Vref is applied at time t2, the output voltage of the comparator 2 remains almost + Vcc because the + input terminal voltage is VH. It does not change.

However, for example, when a voltage of level C slightly higher than VH is applied to the-input terminal at time t3,
The output voltage of the comparator 2 drops from almost + Vcc to almost zero level. In this case, since the output current I2 of the comparator 2 becomes zero and does not flow, the second term on the right side of the equation (12) becomes zero, and the voltage at the + input terminal drops from VH to the reference voltage Vref.

In this state, -even if the C-level voltage applied to the input terminal fluctuates due to noise or the like,
Unless the amplitude of fluctuation toward the low level side falls below the voltage Vref at the + input terminal, the output voltage of the comparator 2 remains almost at the zero level and does not change. That is, the reference voltage Vref of the + input terminal in this case corresponds to the low-level threshold voltage (VL).

Next, for example, if a voltage of a lower level D than the reference voltage Vref is applied to the-input terminal at time t4, the output voltage of the comparator 2 rises from almost zero level to almost + Vcc level as shown by the solid line, The voltage at the + input terminal rises from Vref to VH.

In this state, even if the D level voltage applied to the-input terminal fluctuates due to noise or the like, the fluctuation amplitude toward the high level side is the voltage VH at the + input terminal.
The output voltage of the comparator 2 remains approximately + Vcc and does not change unless the voltage exceeds Vcc. That is, the voltage VH at the + input terminal in this case corresponds to the threshold voltage on the high level side.

As described above, the threshold voltage of the + input other terminal is VH or V with respect to the voltage applied to the − input terminal.
A comparator configured to switch to any one of L is also called a hysteresis comparator, and VH and VL (Vr
The level difference from ef) is called the hysteresis width.

The output voltage Vo (equation (6)) of the amplifier 1 is full-wave rectified as described above, and the DC voltage 2Vo / π smoothed through the low pass filter is
In the comparator 2, it is compared with the threshold voltage VH of the + input terminal.

In this case, assuming that the rectified DC voltage 2Vo / π is at a level equal to or lower than the threshold voltage VH (FIG. 2 (E)), the output of the comparator 2 swings up to a substantially positive power supply voltage + Vcc (FIG. 2 (F)). ). As a result, the diode D is turned on and a current flows through the load resistor R7, and a voltage substantially equal to the positive power supply voltage + Vcc is generated in the resistor R7 (FIG. 2 (g)). Inverter 3 receives this voltage and sends a signal of logic level L to CPU 14.

Even if the data input from the A / D converter 13 indicates an overflow, the CPU 14 connects the battery 11 as a load to the AC constant current source 8 when the logic signal input from the disconnection detection circuit 4 is L. It is determined that the resistance R1
Display that it is necessary to switch the range of 2 to the high resistance side.

Next, the AC constant current source 8 and the load battery 1
1 is not connected to the amplifier 6 of the AC constant current source 8 to the amplifier 1 of the disconnection detector 4, as shown in FIG. 4A, a sine wave whose peak value is almost positive and equal to a negative power supply voltage. A voltage is applied, and almost + on the collector side of the transistor Tr.
A full-wave rectified voltage having a peak value equal to Vcc appears (FIG. 4 (d)).

The positive DC voltage obtained by smoothing the full-wave rectified voltage becomes about 2 Vcc / π (FIG. 4 (E)) and is applied to the-input terminal of the comparator 2 and the threshold voltage VH of the + input terminal. Compared to. In this case, since the threshold voltage VH is set to a level lower than 2Vcc / π, the output voltage of the comparator 2 becomes zero level (Fig. 4 (f)), the diode D is off and its output voltage becomes zero level. (FIG. 4 (g)). Therefore, a signal of logic level H is output from the inverter 3 to the CPU 14
(FIG. 4C).

When the data input from the A / D converter 13 indicates an overflow and the logic signal input from the disconnection detection circuit 4 is H, the CPU 14 connects the battery 11 as a load to the AC constant current source 8. If not, the display unit (not shown) displays the determination result.

Here, the disconnection means that the current path from the AC constant current source 8 to the battery 11 is literally disconnected, and as described above, the probe 9a, 9b is not properly contacted with the battery terminal and the internal state of the battery 11 is deteriorated. Although the increase of the resistance Rs is included, it is possible to consider the measurable rated resistance value by replacing them with the increase of the internal resistance Rs.

That is, the input voltage Vo of the disconnection detection circuit 4
Is represented by Vo = Vi (R12 + Rs) / R12 as shown in equation (6). If the DC voltage 2Vo / π obtained by full-wave rectifying and smoothing this input voltage Vo is equal to or lower than the threshold voltage VH, measurement is possible. For example, if 2Vo / π = VH is set, the equation ( From 6), 2Vi (R12 + Rs) / πR12 = VH From the above equation, R12 + Rs = π · VHR12 / Vi Therefore, Rs = {(π · VH / 2Vi) -1} R12 ... (13) is obtained.

In the equation (13), Vi is the output voltage of the AC constant voltage source 5, VH is a voltage determined by the values of the resistors R4, R5 and R6 for dividing the positive power source voltage + Vcc, and R12.
Is a resistance for setting the measurement current I, and both are known. However, VH> Vi / 2 is required because the value inside the braces must be a positive value.

Rs in the equation (13) corresponds to the measurable rated resistance value, and if it is less than this resistance value, the level of the logic signal sent from the disconnection detection circuit 4 is L, and the measuring unit 15
The value of Rs can be measured at. Since the value of R12 is switched by a range of a plurality of steps at a certain magnification, the measurable rated resistance value of Rs also changes at the same magnification, and the resistance can be measured over a wide range.

As a modification of the above embodiment, the output of the comparator 2 is connected to the cathode side of the diode D and the load resistance is connected to the diode D of the disconnection detection circuit 4 and the load resistance R7 as shown in FIG. R7 is a diode D
Even if the anode is connected to the positive power supply voltage + Vcc, the logic level determination can be made the same as in the above embodiment.

On the other hand, when the logic level judgment is the reverse of that of the above embodiment, that is, when it is attempted to judge the disconnection at the L level, the inverter 3 may be eliminated or replaced with a non-inverter. Good.

Further, with the inverter 3 as it is, the connection of the input terminal of the comparator 2 is connected to the reference voltage Vref by the resistor R5 to the negative input terminal as shown in FIG. 6, and the output voltage Vo of the amplifier 1 is connected. Even if the positive DC voltage obtained by smoothing the full-wave rectified voltage is connected to the + input terminal, the determination of the logic level can be reversed from that in the above embodiment.

[0061]

As described above, according to the present invention,
When the measurement voltage is too high and the A / D converter in the measurement section overflows, the current path from the AC constant current source to the test battery depends on whether the logic signal output of the disconnection detection circuit is L level or H level. The CPU automatically determines whether it is closed or in a disconnection state (no load). Therefore, the device is easy for the user to handle.

Further, since the value of the resistance for measuring current setting can be switched by a range of a plurality of steps at a predetermined magnification, the measurable rated resistance value also changes at the same magnification, and the resistance value can be measured over a wide range. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of an apparatus to which the present invention is applied.

FIG. 2 is a waveform diagram for explaining the operation of each part of the device to which the present invention is applied.

FIG. 3 is a waveform diagram for explaining the operation of the hysteresis comparator in the device to which the present invention is applied.

FIG. 4 is a waveform diagram for explaining the operation of each part of the device to which the present invention is applied.

FIG. 5 is a circuit diagram showing a first modification of the disconnection detection circuit in the device.

FIG. 6 is a circuit diagram showing a second modified example of the disconnection detection circuit in the device.

FIG. 7 is a block diagram showing a schematic electrical configuration of a conventional device.

[Explanation of symbols]

 1.6.7 Amplifier 2 Comparator 3 Inverter 4 Disconnection detection circuit 5 AC constant voltage source 8 AC constant current source 11 Secondary battery (battery) 14 CPU 15 Measuring part I Measuring current R12 Resistance Rs Internal resistance VH High potential threshold voltage Vi AC constant voltage source voltage Vo Output voltage Vref Reference voltage

Claims (5)

[Claims] 1. An AC constant current source supplies an AC current for measurement to a battery to be measured, the AC voltage generated between the terminals of the battery is detected on the measuring unit side, and the AC voltage is converted into a resistance value. In a battery tester that measures the internal resistance of the battery,
The output voltage from the AC constant current source is compared with a predetermined reference value, and the current path between the AC constant current source and the battery is closed or open depending on whether or not the reference value is exceeded. A battery tester comprising a disconnection detection circuit for detecting whether or not 2. The AC constant current source amplifies a constant level AC voltage generated from the AC constant voltage source with an amplifier, and a resistor provided in a current path from the output side of the amplifier to the battery, The disconnection detection circuit is configured to set a measuring AC current flowing through the battery to a predetermined level, and the disconnection detection circuit includes a rectifying and smoothing circuit for converting the amplified voltage of the amplifier into a DC voltage, and the same rectifying and smoothing circuit. A voltage comparison circuit for comparing the direct-current voltage formed in step 3 with a predetermined threshold value, and a logic signal generation circuit for converting the comparison output of the voltage comparison circuit into a voltage signal of logic level L or H and outputting it to the measuring section. When the logic signal is in a predetermined level state, the measuring section determines that the current path from the AC constant current source to the battery is in a disconnection state including a contact failure of the probe. The battery tester according to claim 1, which is a characteristic. 3. The battery tester according to claim 2, wherein the resistance provided in the current path of the AC constant current source is switchable in a plurality of stages with a predetermined resistance value. 4. The voltage comparison circuit of the disconnection detection circuit includes an amplifier to which a DC voltage formed by the rectifying and smoothing circuit is applied to its − input terminal, and the + input terminal of the amplifier has a power source for the tester. A reference voltage obtained by dividing the voltage to a predetermined level and a voltage obtained by dividing the output voltage of the amplifier by 1 / n (n is an arbitrary division ratio) are added. The battery tester according to claim 2, wherein the battery tester operates as a hysteresis comparator in which a threshold voltage of a terminal is switched between high and low. 5. The logic signal of a predetermined level output from the disconnection detection circuit to the measuring unit at the time of disconnection is generated when the resistance of the measurement current path including the internal resistance of the battery is larger than the value shown in the following equation. The battery tester according to claim 2, wherein the battery tester is provided. Rs = {(π · VH / 2Vi) −1} × R12 Rs: Resistance of measurement current path including internal resistance of secondary battery R12: Measurement current setting resistance in AC current source VH: High potential threshold of hysteresis comparator Voltage Vi: AC constant voltage source voltage in the AC constant current source