JPH01318972A - Loop-resistance measuring method - Google Patents

Abstract

PURPOSE:To improve accuracy in loop-resistance measurement of a telephone set which is connected to an electronic switching system by selecting a resistance value so that the I-R characteristics become equal in a simple constitution. CONSTITUTION:The I-R characteristic between a loop resistance R of a telephone set and a measured current I is fluctuated with a current flowing through the telephone set. Therefore, resistors R1-R3 are selected with a range switching point CH so that the current is within a specified range when a loop resistance is measured. In this way, even if the current flowing through the telephone set is fluctuated with the loop resistance, the I-R characteristic becomes equal by the range switching. Therefore, accuracy in loop-resistance measurement can be improved. Even after the range switching at the CH point, the I-R characteristic is under the same condition as before the range switching. Therefore, a reading circuit and a program for processing the measured results can be readily implemented.

Description

[Detailed Description of the Invention] [Summary] Regarding the loop resistance measurement method of a telephone connected to an electronic exchange, even if the loop resistance measurement range of the telephone is switched, I-
The purpose is to have the same R characteristics, and the internal resistance R? □, the sum of the resistance values R of the line resistance RL, and the current flowing through the telephone ■In the ■-R characteristic, the subscriber terminal to which the loop resistance circuit of the telephone is connected,
and L2, the earth is connected to the Ll terminal through the resistor R2, the stationary side of the switching contact CH, and the resistor R3, the battery is connected to the Lz@ terminal through the resistor R1, and the operating side of the switching contact CH is connected to the earth through the resistor R3. A loop resistance measuring circuit is configured to disconnect resistor R2, and a loop resistance measuring device consisting of an operational amplifier for impedance matching, an A/D converter, and a microprocessor is connected to the L2 terminal side of resistor R1 of the loop resistance measuring circuit. Accordingly, the range switching of the r-R characteristic is performed.

[Industrial application field]

The present invention relates to a method for measuring loop resistance of a telephone connected to an electronic exchange.

In recent years, as telephones have become more multi-functional, the circuitry of telephones has also become electronic, and the input signal lines of telephones are equipped with diode bridges to prevent polarity reversal and DC/DC circuits to generate operating power for internal electronic circuits. Due to the connection of a DC converter, etc., the conventional method of measuring loop resistance of 600-type telephones by passing a small current through the telephone, i.e., using a tester, etc., produces a low measurement result due to the low measurement voltage and low measurement current. This results in a resistance value that makes it impossible to determine whether the telephone is good or bad when maintaining the exchange.

In recent telephone sets, the measurement method shown in FIG. 4(a) is used as a condition for measuring the direct current resistance of the telephone loop according to the design standards of the telephone set. That is, the power supply voltage is -48V, and the line resistance R
When changing L, the resistance R□ of the telephone is 5θ~300
The measurement conditions are specified so that the current IL flowing through the telephone is 20 to 120 mA. FIG. 4(b) shows an example of R-1 characteristics of internal resistance and current of an electronic telephone. In the figure, when the current of the phone is in the range of 18 to 25 mA, the change in resistance is 301 to 235 Ω, which is relatively small, but 1
Below 8n+A, the resistance value fluctuates greatly. Therefore, when measuring the loop DC resistance of a telephone, a measuring circuit must be constructed taking the above conditions into consideration.

[Conventional technology]

A conventional loop resistance measuring circuit is shown in FIG. In the figure, 1 is a loop resistance circuit of a telephone, 2 is a loop resistance measuring circuit, 3 is an operational amplifier, 4 is an A/D converter, 5 is a microprocessor, and 6 is a loop resistance measuring device.

The loop resistance circuit 1 of the telephone set is represented by the resistance value R, which is the sum of the telephone resistance R1° and the line resistance RL, and the loop resistance measuring circuit 2° consists of resistors R, R2, and R3, and L,,L! It is connected to the loop resistance circuit 1 of the telephone through the terminal to form a loop resistance measuring circuit, and is connected to the loop resistance measuring device 6 through the connection point of R2 and R3 using the resistance comparison measuring method. The loop resistance measuring device includes an operational amplifier 3 for impedance matching, an A/D converter 4 for analog/digital conversion, and a microprocessor 5 for performing digital calculation processing.
The voltage VI at the connection point of R2 and R3 is matched to the impedance from the H impedance, and is converted into a digital value and counted as a digital value to obtain the telephone resistance value R.
Convert to .

In this conventional resistance comparison measurement method, current is passed over a wide range to measure the loop resistance, so as the line resistance increases, the measured current decreases, and the internal resistance of the phone increases rapidly, resulting in a high resistance value. It fluctuates and gives the same results as traditional testers, making it impossible to judge whether the phone is good or bad. On the other hand, if the line resistance is low and the current value increases, the 1-R characteristic of the electronic telephone becomes steep and the measured value of resistance becomes unstable. Therefore, in order not to change the IR characteristic, the resistance values R+, R2, and R8 of the loop resistance measuring circuit 2' must be appropriately selected.

[Problem to be solved by the invention]

As described above, in the conventional loop resistance measurement method, the internal resistance of the telephone fluctuates due to fluctuations in the measured current due to changes in line resistance. Therefore, in the present invention, the measured current is kept within the design specifications of the telephone, and is kept at a certain level. The purpose of this invention is to provide a resistance comparison measurement method that reduces fluctuations in the internal resistance of a telephone by performing measurements under these conditions, and that ensures that the I-R characteristics remain the same even when changing measurement ranges. do.

[Means to solve the problem]

FIG. 1 shows a basic configuration diagram of the loop resistance measuring method of the present invention. In the figure, 1 is a telephone loop resistance circuit consisting of a telephone resistor R and a line resistance RL, and 2 is a resistor R, , R, ,
A loop resistance measurement circuit consisting of R3 and a switching contact CH, 3 an operational amplifier for impedance matching, 4 an A/D converter for analog/digital conversion, 5 a microprocessor for converting counts into digital values, and 6 a loop resistance measurement circuit. Show the device.

A loop resistance circuit 1 of a telephone set is a circuit to be measured, and is indicated by a resistance value R, and a loop resistance measuring circuit 2 is connected to terminals . The operational amplifier 3, the A/D converter 4, and the microprocessor 5 constitute a loop resistance measuring device 6 that converts the telephone loop resistance R into a digital value. The switching contact CH of the loop resistance measuring circuit 2 has a function of disconnecting the resistor R2 from the measuring circuit by relay operation.

[Effect]

In order to explain the present invention in detail, FIG. 2 shows the TR characteristics of the telephone loop resistance R and the measured current (2).

In the figure, if the horizontal axis is the loop resistance value R (KΩ), which is the sum of the internal resistance of the phone and the line resistance, and the vertical axis is the current value I (mA) flowing through the loop resistance measurement circuit, then the current flowing through the phone causes a direct current. Since the loop resistance varies significantly,
The resistance Rr of the loop resistance measurement circuit is
Select Rz and R3.

Therefore, in a range where the loop resistance R is low, the resistance of the loop resistance measuring circuit 2 is increased to decrease the current value, and in a range where the loop resistance R is high, the resistance of the loop resistance measuring circuit 2 is decreased to increase the current value. That is, when the measurement current flowing through the telephone becomes 20mA or less, the switching contact CH is operated to switch to the next range, and the resistance value R is set so that measurement can be performed within the range of 20 to 30mA under certain conditions.
Select RZ and R3. Further, even after range switching is performed using the CH contact, the I-R characteristics remain the same as before range switching, so the reading circuit and measurement result processing program can be easily implemented. Note that the dotted line portion of the curve is a curve created by a conventional circuit that does not perform switching, and the I-R characteristic becomes steep, making it unsuitable for measurement.

〔Example〕

A circuit configuration diagram of an embodiment of the present invention is shown in FIG.

In the figure, 1 to 6 indicate the same numbers as in the principle configuration diagram of FIG. 1. The telephone internal resistance R setting of loop resistance circuit 1 is 300
Ω or less, and line resistance RL is 1200Ω or less,
The telephone loop resistance R will be 1500Ω or less. Also, set the resistances R+, Rz, and Rs of loop measurement circuit 2 to 7 each.
00Ω, 800Ω, and 100Ω, the measurement result of the telephone loop resistance R is calculated from the voltage ■1 applied to the resistor R1 of the loop resistance measurement circuit 2 using the following formula R, +R2+R,, +
RRI ■ = Power supply voltage 48V Here, ■ draws a characteristic curve as shown in Figure 2, but 1 =
If it is 20 mA or less, that is, if it is read as V, = 2V or less, the CH relay contact is activated and the resistor R1 is disconnected. Telephone loop resistance RR at this time = −R:l −
(R+ +R1) (Ω), and the I-R characteristic in this case draws the same curve as the I-R characteristic when R2 is included. Therefore, by switching the 800Ω of resistor R2 with the CH contact, the measurement curve can be changed. It can be kept in the range of 20 to 30 mA.

〔Effect of the invention〕

As described above, according to the present invention, the I-R
By selecting a resistance value that makes the characteristics the same,
Improves the accuracy of loop resistance measurements for telephones connected to electronic exchanges. Furthermore, even if the measurement range is changed, the same measurement result reading circuit configuration can be used, and the result processing program can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle configuration of the present invention, Fig. 2 is an IR characteristic diagram explaining the invention in detail, Fig. 3 is a circuit diagram of an embodiment of the invention, and Fig. 4 is a diagram of an electronic telephone set. A loop resistance measurement condition diagram, FIG. 5, shows a circuit configuration diagram of a conventional example. In the figure, 1 is a telephone loop resistance circuit, 2.21 is a loop resistance measuring circuit, 3 is an operational amplifier, 4 is an A/D converter, 5 is a microprocessor, and 6 is a loop resistance measuring device.

Claims (1)

[Claims] Internal resistance R_T_E_ of a telephone connected to an electronic exchange
In the IR characteristic that compares the resistance value sum R of L and line resistance R_L and the current I flowing through the telephone, the telephone has subscriber terminals L_1 and L_2 that connect the loop resistance circuit (1) of the telephone, Connect the resistor R_2 to the L_1 terminal, the stationary side of the switching contact CH, and the earth through the resistor R_1, connect the battery to the L_2 terminal via the resistor R_3, and disconnect the resistor R_2 on the operating side of the switching contact CH. A resistance measurement circuit (2) is configured, and an operational amplifier (3) for impedance matching is connected to the L_2 terminal side of the resistance R_3 of the loop resistance measurement circuit (2).
A loop resistance measuring method characterized in that a loop resistance measuring device (6) consisting of a D converter (4) and a microprocessor (5) is connected to perform range switching of the above-mentioned I-R characteristic.