JPS5813642Y2 - Signal loopback test circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a signal loopback test circuit used for local testing in a four-wire transmitter/receiver such as a data transmission modulator/demodulator.

In a transmitting/receiving device having a transmitting circuit and a receiving circuit,
If the transmission and reception of signals becomes impossible due to some kind of failure,
A signal loopback test circuit is generally provided to confirm the operation of the own device or to confirm the presence or absence of an abnormality in the transmission line and reception line and to localize the faulty part.

In particular, in the case of a 4-wire type, the function of the own device is checked locally by connecting its own transmitting output end to the receiving input end, and the signal from the receiving line is connected to the transmitting line to connect the transmitting line and the receiving line. Conventionally, a circuit as shown in FIG. 1 has been used, which makes it easy to check whether there is any abnormality in the circuit.

That is, in this circuit diagram, a transmitting circuit SS such as a modulator and a receiving circuit SR such as a demodulator are connected to a four-wire line L1 . It is connected to L2, and along with this both circuits SS,
Switching contacts S1, S2, 53S4 for loop testing are inserted between SR and each transformer TI, T2, and under normal conditions both circuits SS, SR and each transformer TI, T2 are connected. During the return test, both circuits SS and SR are connected by the operation of switching contacts 81 to S4, and the transmission circuit SSq
A transmission output is given as a reception input of a reception circuit SR, and a transmission transformer T1 and a reception transformer T2 are connected so that a signal from a reception line L2 is supplied to a transmission line LIK.

However, the signal current flowing through the switching contacts 81 to S4 is an extremely weak alternating current, and in order to obtain the reliability of contact contact, expensive contacts such as all contacts and gold-plated contacts must be used. ~S4 is rarely used other than during loop tests, and because the number of operations is extremely small, it is difficult to maintain a good contact state at all times.
This defective contact of the changeover contact for the folding test has resulted in a drawback in that the reliability of the device is reduced.

The purpose of the present invention is to eliminate such drawbacks of the conventional method, and includes a DC sending circuit and a DC receiving circuit that constantly flow DC current to the switching contact, and by superimposing the signal current and the DC current, the switching contact is always connected. It provides an extremely useful signal loop test circuit that activates and maintains good contact conditions.

The details of the operation will be explained below with reference to FIG. 2 showing an embodiment of the present invention.

In this circuit diagram, a transmitting circuit ss and a receiving circuit SR
For example, on one side of the transmission circuit SS, for example, a DC transmission circuit DS including a resistor R1 and a positive electric current generator B is provided. This DC current is superimposed on the signal current as a ceiling current to activate the switching contact.

In addition, the negative electrode side of the positive electrode generator B is connected to the ground circuit in the case of the same figure.

The other of the switched transmitting circuit SS and receiving circuit SR, in this case the input side of the receiving circuit SR, is provided with a DC receiving circuit DR consisting of a negative power supply -B and a resistor R2, and under normal conditions, the switching point S3
, S4 and the secondary winding S of the receiving line transformer T2 to obtain the same effect as described above.

It goes without saying that the positive side of the negative power source -B is connected to the ground circuit.

Next, when the switching contacts S 1 and S4 are operated during the return test, the positive power source B and the negative power source -B are connected in series via the earth circuit, so the switching contacts S 1 and S4 are operated from the DC sending circuit DS.
, S4 to the DC receiving circuit DR, activating the make side of the switching contacts St and S4.

Furthermore, a resistor is installed in the line signal return circuit that connects switching contacts s2 and 83, which are provided to connect the secondary winding S of the receiving line transformer T2 to the primary winding PK of the transmitting line transformer T1 during the return test. DC sending circuit D between R3 and Seiden Gensei B
A DC receiving circuit DR is provided which connects to sX or negative power supply -B, and when the switching contacts S2 and 83 are operated during the return test, this DC sending circuit DSL or DC receiving circuit DR is connected.
and the primary winding P of the transmission line transformer T1 and the secondary winding S of the reception line transformer T2, respectively, by switching contacts S2. S3
A direct current is passed through the switching contacts S2. Activate the make side of S3.

Therefore, not only during normal times but also during folding tests, contact failures do not occur in the switching contacts 81 to 84, and the reliability of the device as a whole is significantly improved.

Incidentally, although the capacitors CI and C2 are for DC blocking, they may be omitted depending on the conditions of the transmitting circuit SS1 and the receiving circuit SR.

If the relationship between the voltage of the positive power source B and the resistance value of the resistor R1, the relationship between the voltage of the negative power supply B and the resistance value of the resistor R2, and the relationship between the resistance value of the resistor R3 are appropriately selected, normal The value of the DC current flowing through the switching contact can be made the same during the test and the loop test.

In addition, as the DC sending circuit DS and the DC receiving circuit DR, blocking wires or the like may be used instead of the resistors R1 to R3.

Instead of the DC sending circuit DSL or the DC receiving circuit DR connected to the transmitting circuit SS and receiving circuit SR, a predetermined bias potential is applied to the final stage amplifier of the transmitting circuit SS and the manual stage of the receiving circuit SR. , capacitor CI, C2
may be omitted and at the same time provide a potential difference between one bias potential and the other bias potential.

It goes without saying that the same operation can be achieved even if the DC sending circuit DR is provided on the input side of the receiving circuit SR and the DC receiving circuit DR is provided on the output side of the transmitting circuit SS.

Note that the value of the direct current may be determined depending on the current capacity and material of the contact, but generally a small current of about several mA is sufficient.

It is clear that the circuits shown in FIGS. 3 to 5, in which the structure of the switching contacts is partially simplified, operate in the same manner.

In addition, switching contact S2. In order to ensure the effect of the superimposed current during the S3 loopback test, a capacitor C3 is inserted in the middle of the line signal loopback circuit as shown in Figure 6, and a DC sending circuit or DC receiving circuit is installed at both ends of the capacitor C3. It's okay.

The method for inserting a capacitor into the housing can be similarly applied to Fig. 3, which partially simplifies the configuration of the Q-switching contact, and also to Figs. 4 and 5. Between the connection point of the primary side P of the transformer T1 and the switching contact s1 and the DC reception circuit DR, FIG. A similar application can be made by inserting a capacitor between the two.

As is clear from the above explanation, according to the present invention, the switching contacts for signal loopback tests are always activated and a good contact state is maintained. This makes it possible to apply contact points, improve the reliability of the entire device, and reduce costs, resulting in great effects in various transmitting and receiving devices.

[Brief explanation of drawings]

Figure 1 is a signal loop test circuit diagram showing a conventional example, Figures 2~
FIG. 6 is a signal loopback test circuit diagram showing an embodiment of the present invention. SS...Transmission circuit, SR...Reception circuit,
T1...Transmission line transformer, T2...Reception line transformer, Ll...Transmission line, Ll...
・Reception line, S1 to S5...Switching contact, DS・
...DC sending circuit, DR...DC receiving circuit, 10B...positive power supply, -B...negative power supply,
R1-R4...Resistor.

Claims (1)

[Scope of utility model registration request] A transmitting circuit and a receiving circuit are connected to the four-wire line via a transmitting line transformer and a receiving line transformer, respectively, and a switching contact for a loop test connecting the transmitting circuit and the receiving circuit, and a transmitting line transformer and a receiving line. In a 4-wire transmitting/receiving device having a switching contact for folding tests that connects a line transformer,
The transmitting circuit is provided with a circuit that causes a direct current to flow through the switching contact and the transmitting transformer on the transmission line side, and the receiving circuit is provided with a circuit that causes a direct current to flow through the switching contact and the receiving transformer on the receiving line side. , a signal loopback test circuit comprising: a line signal loopback circuit that loops back a signal from the receiving transformer to the transmitting transformer via the switching contact on the transformer side; and a circuit for passing a direct current.