Some Definitions About Tdr

Some Definitions about TDR

• In copper cabling, TDR can measure cable length and locate specific areas of impedance mismatch by transmitting a fast rise-time pulse down the cable under test and then monitoring the cable for constant voltage in order to detect any reflections of the transmitted pulse. Any anomalies in the cable that change the capacitance, inductance, or resistance will result in measurable differences in impedance. Think of impedance mismatches as disruptions in the flow or back-pressure that alter the actual time for propagating the pulse vs. the nominal propagation rate. These impedance mismatches anywhere along the length of the cable cause reflections that are then displayed on the TDR's output. A significant reflection also always occurs at the end of the cable.

• If a cable is metal and has at least two conductors, it can be tested by a TDR. Devices with TDR capabilities will troubleshoot and measure all types of twisted-pair and coaxial cables, both aerial and underground. Based on the cable's nominal velocity of propagation (NVP), which is dialed into the TDR prior to testing, the unit can measure the time it takes for the transmitted pulse to be reflected from the far end of the cable. By manipulating the instrument's controls, it's possible to calculate the absolute length with some degree of accuracy.

• However, TDR functions integrated directly into cable testers have become more advanced, making it easier to operate them and much simpler to interpret the results.

Ideas for Quick Profit

Using SD(Speedy Delivery), which is a modified version of TDR, I believe the following tasks can be performed in a more accurate manner.

Trouble Shooting Service

• The integration of full-featured TDR capabilities into multi-function field test equipment makes it possible for field installers to leverage the devices' familiar operating interface, while also accessing the power of TDR. Such a device can provide an accurate picture of the TDR trace, showing the distance to the event as well as the event's magnitude. For field-level troubleshooting, the ability to discern differences in the magnitude can be quite helpful for locating return loss failures and identifying marginal problems or latent issues even when the overall link may not be exhibiting a “hard failure” on total impedance tests. Visual displays, such as the one shown in the Figure, can enable the user to identify the precise distance to an anomaly or “event” anywhere along the length of cabling. While this doesn't tell the installer exactly what's wrong, showing them where to look can streamline the troubleshooting process.

Irrigation system

• Time-domain reflectometry (TDR) is a fairly new technique you can use to estimate soil-water content. You direct an electromagnetic pulse down parallel wave guides in the soil. You then use an instrument to measure the speed at which this pulse travels to the end of the wave guides and returns. This technique is based on the dielectric constant of water, which is much higher than that of mineral soils. Salinity can influence the results, although researchers are developing new techniques to overcome this problem. Its major drawback at this time is cost.

Example of Tools already being developed

(SD can greatly increase the capabilities by providing greater accuracy)

Soil Monitoring System - Trase

Trase is the only self-contained TDR instrument capable of investigating and monitoring not only soils, but a wide variety of other materials as well. It is fully field portable, and when you need to leave it at a remote site for several days or weeks, it can be accessed from home or office. On site, Trase quickly measures the dielectric and subsequent moisture properties of soil, seeds, or other materials at a specific location, or, with the optional Trase Multiplexer, at up to 256 locations. Trase automatically logs your sensors at intervals ranging from once a minute to once a day. Using diverse waveguide configurations and associated conversion tables, Trase rapidly measures new or unusual materials. (Soilmoisture can supply these nonstandard TDR tools or you can develop your own). Your ability to make a measurement using Trase is limited only by your imagination and creativity.

DESIGNED AND BUILT TO MEET TOMORROW'S NEEDS

Trase is future-proof. It's the only TDR instrument constructed with open system architecture.