JPS6241261Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the resistance unbalance value of two resistors having almost equal resistance values. In particular, the present invention relates to a resistance unbalance measuring device suitable for automatically measuring the resistance unbalance of a pair of cables.

In a communication pair cable, it is necessary that the resistance values R _x1 and R _x2 of the paired conductor wires are equal, and the cable is designed and manufactured so that this unbalance value ΔR = R _x2 - R _x1 (1) is within the permissible range. Ru. For this reason, it is necessary to perform a test to measure the unbalance value for many pairs in cable manufacturing or cable installation work, and a highly accurate and simple measuring device is required for this purpose.

A typical example of a measuring device conventionally used for this purpose is shown in FIG. This is an application of the well-known Wheatstone bridge, in which the far ends of the cable pair to be measured are short-circuited and grounded, and the near ends are connected as part of the bridge arm as shown in the figure to perform measurements. To briefly explain the principle of operation, first, when the SW is closed, the bridge is almost in equilibrium when R _s = 0, so the reading on the voltmeter V at this time is V ₀
get. Next, when the switch is opened and the reading of the voltmeter V is obtained, V ₁ is obtained, the following approximate solution is obtained: ΔR=R _x2 −R _x1 ≒±V ₀ /V ₁ R _s (2) (Since this is a conventional technique, the process is omission).

This method requires two instrument readings and calculations during measurement, and the operation of the bridge circuit is complicated, so it takes time and effort to obtain results. Also, because it reads the slight fluctuation of the voltmeter, individual differences are likely to occur. Furthermore, when the unbalance value is large, the approximation no longer holds true, which results in errors in the measurement results obtained by equation (2), which has the disadvantage that measurements over a wide range cannot be performed.

The present invention improves on this by making it possible to measure unbalanced resistance values over a wide range with high precision and without induced noise.
Moreover, it is an object of the present invention to provide a device capable of automatic measurement.

The present invention has a constant current power supply circuit that connects two resistors to be measured in series without passing through a common potential point and provides equal current from both ends, and uses high impedance The feature is that a voltage proportional to the resistance unbalance value is obtained by extracting the voltage through a circuit and adding the voltage.

The present invention will be described in more detail below with reference to the drawings of the embodiments.

FIG. 2 is a circuit diagram of the apparatus according to the present invention. In the figure, R _x1 and R _x2 are two resistances to be measured, which are connected in series at point c. Constant current power supply C _u
One end of is grounded to a common potential point, an output end is connected to end a of R _x1 of the resistance to be measured, and a coupling point c is connected to the common potential point via a resistor R _c .

Also, in the figure, A ₄ is a differential amplifier, and the connection point c
The potential of is connected to the negative input of differential amplifier A ₄ , the common potential point is connected to the positive input of differential amplifier A ₄ ,
The output of the differential amplifier _A4 is connected to the end b of the resistance to be measured _Rx2 .

A ₁ and A ₂ are provided with sufficient negative feedback to the operational amplifiers, and operate as gain-of-1 buffer amplifiers with high input impedance. The potential difference with respect to the connection point c that occurs across the ends a and b of the resistors R _x1 and R _x2 coupled in series is the buffer amplifier A ₁ and
_A2 and summingly coupled by resistors _R1 and _R2 at the input of operational amplifier _A3 .

That is, if the potential difference between point a and point b with respect to coupling point c is V ₁ and V ₂ , amplifiers A ₁ and A ₂ are buffer amplifiers with a gain of 1, so this appears as is in the output. If the resistance values of the resistors R ₁ and R ₂ are set to the same value R, the output voltage V ₀ of the operational amplifier A ₃ becomes V ₀ =R ₃ /R(V ₁ +V ₂ ) (3). Here, since V ₁ and V ₂ have opposite signs, equation (3) is a value V ₀ proportional to the unbalanced value ΔR (=R _x2 - R _x1 ) of the resistances to be measured R _x1 and R _x2 . =iR ₃ /R·ΔR (4).

If the output V ₀ is led to a voltmeter V and this is displayed as a resistance value, the unbalance value can be directly read. Furthermore, if the output V ₀ is guided to an automatic recording device and recorded, an automatic measuring device can be constructed.

For now, the output current i of the constant current power supply C _u is
When R ₁ = R ₂ = R ₃ = R is set at 1 mA, when measuring the unbalance of the pair of cables, assume that R _x1 = 1000Ω and R _x2 = 1001Ω. At this time, the output V ₀ is 1 mV, which indicates an unbalance of 1 Ω.

Using this same measuring device, when we next measure a pair of cables with R _x1 = 10000Ω and R _x2 = 10001Ω, the output
V ₀ is 1 mV, indicating an unbalance of 1 Ω. In this way, regardless of the size of the resistance to be measured, ΔR can always be directly displayed, making it extremely useful as a field measuring instrument for communication cables.

The operation of the constant current circuit of this example circuit will be explained.

When a constant current i is supplied from a constant current power supply C _u to a loop of a resistor R _x1 and a resistor R _c , a potential difference across the resistor R _c is applied between the positive and negative inputs of the differential amplifier A ₄ . If the gain and output capacitance of the differential amplifier _A4 are sufficiently large, a negative current is applied to the output so as to make this potential difference zero, and the current in the resistor _Rc is balanced at a value that makes it zero. At this time, a current i flows through the resistor R _x2 as shown by the arrow in the figure, and the resistor R
This is equivalent to applying a current in series to _x1 and R _x2 . In this way, in a balanced state, no current flows through the resistor R _c , so the potential at point c is equal to the common potential, and the value of the resistor R _c does not matter. In other words, if the value of the resistor R _c is set large, the resistances to be measured R _x1 and R _x2 are floating from the ground, and if the value of the resistor R _c is set small, the two resistances to be measured R _x1 and R _x2 are floating. The connection point is grounded.

In this embodiment circuit, one end of the constant current power supply _Cu is grounded, which has the advantage of being free of induced noise, and since there is no ground point for either of the resistances to be measured _Rx1 or _Rx2 , there is an advantage that the resistances can be used in a balanced state.

As mentioned above, the device of the present invention can obtain a voltage proportional to the resistance unbalance value at the output, so it can perform measurements over a wide range with high precision. The unbalanced value can be obtained using a voltmeter, and there is no noise associated with the measurement.

Note that the high input impedance buffer amplifier mentioned in the above example can also be implemented using other high impedance circuits, and the adder circuit can also be implemented using a circuit with a similar function other than the above example. The invention can be implemented similarly.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional resistance unbalance value measuring device. FIG. 2 is a circuit configuration diagram of an embodiment of the present invention. R _x1 , R _x2 ... Resistance to be measured, C _u ... Constant current power supply, A ₁ to _{A 2} ... Amplifier, R ₁ to R ₄ , R _c , R _s , R
...Resistor (its resistance value).

Claims (1)

[Claims for Utility Model Registration] A constant current power source C _u that applies a constant current to two resistors to be measured (R _x1 and R _x2 ) connected in series at a connection point C; resistance to be measured (R _x1
and R _x2 ) and _{the above - mentioned} connection _point C. In the resistance unbalance measurement device, the constant current power supply has one end connected to a common potential point, and an output end connected to the two connected in series. The connection point C is connected to the negative input, the positive input is connected to the common potential point, and the output is connected to the other end of the two series-coupled resistors to be measured. The adder circuit has a differential amplifier _A4 connected to it, the coupling point C is connected to a common potential point via a resistor _Rc , and the adding circuit has one end of its input and output connected to the common potential point. A device for measuring a resistance unbalance value, comprising: a voltmeter that displays the output voltage of the adder circuit as a resistance value.