JPS62199127A - Cable delay measuring instrument - Google Patents

Abstract

PURPOSE:To attain the measurement with high accuracy and the simple and accurate adjustment of a delay value by measuring the delay time between a pulse fed from one end of a cable and a pulse reflected from the other open end. CONSTITUTION:A pulse from a pulse generator 1 is divided into two by a distributor 2; one is fed to a frequency counter 3 and the other is fed to one end of a cable Gx whose other end is opened. Then the pulse reflected from the other end is fed to the counter 3 via the distributor 2 similarly and the time delay of detection of both pulses corresponding to the delay in the cable Cx is measured with high accuracy by the constitution not requiring a connector to both ends of the cable. The delay adjustment of the cable whose one end is opened is executed simply and accurately.

Description

[Detailed Description of the Invention] [Summary] The present invention applies a pulse signal from one end of a cable and measures the delay time of the pulse signal reflected from the other end. Since the other end of the cable is an oven, it can be canted and the desired value of delay time of the cable can be obtained.

[Industrial application field]

The present invention relates to a time measuring device, and more particularly to a cable delay measuring device for measuring delay time caused by a cable.

[Conventional technology]

When high-speed processing is required in data transmission equipment, control equipment, etc., it is necessary to specify the delay time of the cable that connects the circuits that make up the equipment.For example, by applying clock pulses to multiple circuits, When outputting data or importing data in synchronization with the data, these multiple circuits must operate simultaneously. However, when the lengths of the cables that apply the clock pulse to each circuit are different, a delay time corresponding to the difference in length occurs, and even though all the circuits are synchronized, there is a delay due to variations in the output signal etc. Occur.

Furthermore, in high frequency circuits and the like, when the entire system is adjusted in consideration of a specific delay time, the same cable must be used. That is, since the adjustment includes the delay time of the cable, it will not be possible to obtain the same characteristics as during adjustment unless the same cable is used.

For this purpose, cables with a specific delay (delay time) are currently created and used.

To create such cables, three types of measurement methods are conventionally used:

The first method is to apply pulses generated by a pulse generator to one end of a cable, and measure the time it takes for a signal applied from one end of the cable to be output from the other end of the cable using an oscilloscope or the like.

The second method is to measure the cape-by round trip time of the reflected wave using the TDR method. The third method is to use an oscilloscope to observe the signal between both ends of the cable, change the transmission frequency of the generator so that the signals are in the same phase, and calculate the delay between the two points from this frequency. .

[Problem that the invention seeks to solve]

In the conventional method described above, 1. The second method has the problem that it is difficult to measure with high precision. For example, 50pa (picosecond: 10”e)
In order to obtain the following accuracy, the delay of the cable under test is limited to 500 μs or less.

In addition, since the first to third methods apply a signal from one end of the cable and use the signal obtained from the other end, connectors etc. must not be provided at both ends of the cable under test. This is because when time is an issue, unless a connector for the characteristic impedance of the cable is used, a change in delay time will occur due to a change in the characteristic impedance, and this change will lead to an error.

If the cable has connectors on both ends,
Even if the delay time of the cable under test can be measured, in order to obtain a cable with the desired value, it is necessary to adjust the cable length after measurement, reconnect the connector, and measure whether the desired delay time is obtained. I have to. Such connection processing is complicated, and it is difficult to achieve the desired value with high precision.

The present invention has been made to solve the above-mentioned problems, and its object is to provide a cable delay measuring device that can measure with high precision and that can be easily adjusted to a cable having a predetermined delay value.

[Means for solving problems]

The present invention includes a pulse generator that repeatedly generates pulses, a first pulse detection means that detects the pulses generated by the pulse generator, and a pulse generator that applies the pulses generated by the Halsge generator to one end of a cable to be measured.
a second pulse detection means for detecting a pulse reflected at the other end of the cable under test; and a detection means for detecting the time of the pulse detected by the first pulse detection means and the second pulse detection means. It is characterized by becoming.

[For production]

The pulses generated by the pulse generator are
Detected by pulse detection means. In addition to one end of the cable to be measured, the second pulse detection means detects a pulse reflected at the other end of the cable to be measured. The pulse generator repeatedly generates pulses, and includes detection means for detecting the time of the pulses. Measuring the time difference between the detection signals from the second pulse detection means For example, the detection means for detecting the pulse time is an oscilloscope, and since pulses are repeatedly output from the pulse generator, the oscilloscope can be used to detect the first and second pulses. The time difference between the outputs of the pulse detection means is displayed.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

The pulse generator (PC) is a circuit that generates pulses of a specific period in response to a trigger signal applied from the controller 8 to external trigger signal terminals (EXT, TRIG,). The pulses generated by this pulse generator are applied to a distributor 2 in which three resistors are star-connected, and are divided into two. One of the two divided pulses is sent to the coaxial cable C.
1 to the frequency counter 3. The other end is connected to the coaxial cable that is the cable to be measured via the coaxial cables C2, Ca, and Cb and the connector 4.

The characteristic impedances of the coaxial cables C+, Ca, Cb, and Cx are, for example, Ω-based cables, and the pulse generator 1 and distributor 2 also have a similar group Ω-based impedance.

On the other hand, between cable C2 and Ca, cable Ca and cable 0
A probe 5.6 is connected to each of the two sides. In Fig. 1, point A is indicated by a line.

B represents the connection of the probes 5 and 6, which is a circuit in which the characteristic impedance does not change. Therefore, the pulses generated from the pulse generator 1 are divided into two by the distributor 2, and then passed through the cable C21C without any reflection.
a, Cb and then passes through connector 4 to cable Cx
join. The other end of the cable Cx is open, and the pulse signal reflected here is routed in the opposite direction to the distributor 2.
via the pulse generator 1 and the frequency counter 3 to which the cable C1 is connected.

The above operation causes the pulse signal to propagate within the cable. In the above-described configuration, the probes 5゜6 are connected to points A and B, respectively, where the pulse signal propagates, so that the pulse signal generated by the pulse generator 1 and propagating in the right direction in the figure and the open cable Cx Combined pulse signals with the reflected pulses reflected at the ends are applied to probes 5 and 6, respectively. The probe 5.6 is connected to an oscilloscope 7, and the oscilloscope 7 displays the waveform of the aforementioned composite pulse signal at points A and B on the same cathode ray tube surface, for example.

(Basic measurement of the present invention) Figure 2 shows point A when cable Cx is not connected.

3 is a waveform diagram of a composite pulse signal at point B. FIG.

The value that was 0 level becomes the specific voltage V+ due to the pulse signal from the cable 02 side. And cable Ca,
It is reflected at the connector 4 via Cb, and is further reflected by the cable Cb,
The pulse signal returns to point A via Ca. When returning to point A, the voltage value changes to v2. Although not shown, when the pulse signal becomes 0, the voltage value at point A decreases in a similar manner. In this stepwise change, the middle point a of the first rise and the middle point b11 of the second rise
The time delay is 2. ([)a+Db) due to the time delay Da and Db caused by the cables Ca and Cb.
It can be expressed as Moreover, if point B is based on the intermediate point all, the intermediate point ai2 becomes the time delay Da, and the intermediate point b1
2 becomes ]) a+2·Db (=Do).

Figure 3 shows point A and point when cable Cx is connected.

FIG. 3 is a waveform diagram of a composite pulse signal of B. FIG. The time delay between the intermediate points a2+ and b21 in the composite pulse at point A is expressed as 2 (Da+Db+Dx). In addition, Dx
is the delay time of cable Cx. As mentioned above, the pulse signal is delayed from the intermediate point a21 to the intermediate point b2+ by the cable Ca.

This is the time it takes to go back and forth between Cb and Cx. Also, each intermediate point a22 at point B. b22 becomes Da and Da+2Db+2Dx (=D+), respectively, if the intermediate point a21 is used as a reference.

As is clear from the above-mentioned time delay Do and time delay Dl, the delay time Dx of the cable under test Cx is ′・・
・ ・ ・+11.

The explanation will be given by returning to FIG.

The oscilloscope 7 is, for example, a sampling scope, and the sampled waveform is applied to the controller 8.

The controller calculates and displays the delay time when the cable is connected using the above-mentioned formula from the added sampling waveform.

As mentioned above, the oscilloscope 7 has a display means such as a cathode ray tube. Using the waveform displayed on the cathode ray tube, it is also possible to determine the delay time Dx of the cable under test from the delay time when the cable under test is not connected and the delay time when the cable under test is connected.

In the embodiment of the present invention, the other end Y of the cable to be measured is always open. Therefore, when obtaining a cable having a desired delay time, the other end Y of the cable to be measured is cut with a cutter or the like, and the measurement is performed using the method described above.

As a result of the measurement, if it is necessary to further cut the cable under test, perform the above-mentioned cutting step 1. Repeat measurement.

In the present invention, as mentioned above, the other end Y of the cable to be measured is not connected to anything and is in an open state.
Even if cutting is required after taking a measurement, we don't just cut, we cut and measure.

can be done smoothly.

〔Effect of the invention〕

As described above, according to the present invention, a cable having a desired time delay can be obtained by connecting one end of the cable and leaving the other end open, and the measurement thereof is also highly accurate. It is possible to obtain a cable delay measuring device that can measure with high precision and that can be easily adjusted to a cable having a predetermined delay value.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of an embodiment of the present invention, and Figure 2 is point A when no cable is connected. Waveform diagram of the composite pulse signal at point B. Figure 3 is a waveform diagram of the composite pulse signal at points A and B when the cables are connected. 1...Pulse generator, 3...Frequency counter, 5.6. ...Probe, 7.Oscilloscope, 8.Controller. Δkl Otsukazuki Φfu (way, Itari no Me A δ-Koba (Ashi Go 1) Kea Sore Cx Ii When the concubine is prosperous, A,
赳Bmemo ≧η
Notsu Sosho Singing Figure 3

Claims (1)

[Claims] A pulse generator that repeatedly generates pulses; a first pulse detection means that detects the pulses generated by the pulse generator; a second pulse detecting means for detecting a pulse reflected at the other end of the cable to be measured; and a detecting means for detecting the time of the pulse detected by the first pulse detecting means and the second pulse detecting means. A cable delay measuring device characterized by: