Video: ET91

Video transcript

What the ET91 measures on power line carrier and FDM systems, how it is connected, and how it runs tests from one end of a line, or from both. A power line carrier link, or an FDM system, carries many channels side by side. To commission or maintain one, you have to inject a known signal, and then measure the level of exactly one frequency among all the others, on a line that may be in service. The ET91 is a generator, a selective and wideband level meter, a measuring bridge and a high-resolution spectrum analyser,

all from 100 hertz to 2400 kilohertz, in one-hertz steps, and on battery for about 8 hours. Everything is driven from the menus on the colour display. The 6 function keys below it change meaning with each mode. Numbers, cursors, enter and escape on the right, start and stop to run the measurement, and 4 LEDs for mains, charge, measurement and remote control. On the top panel: the input for the mains or car adapter, a USB port for the PC and another for a memory stick. Then L2, the output, and L1, the measuring input,

each one balanced, on 4 millimetre sockets, and coaxial, on BNC. Switch on: the battery level appears, then a self-test, and the main menu. Before measuring, calibrate the level: connect L1 to L2 with the balanced cable, press CAL, and continue. The calibration then holds until the next one. FDM test instructions give the frequency as carrier plus or minus tone. The ET91 takes it in exactly that form: type the carrier, type the tone, and it tunes itself.

Five bandwidths, from 20 hertz to 3.1 kilohertz, and a minimum and maximum limit give a pass or fail at once. In transmitter and receiver mode it sends on L2 and measures on L1 at the same time. In tracking mode the receiver follows the generator by itself: change the audio test tone, and the meter moves to carrier plus or minus that tone, without touching it. On a working PLC line, the instrument is connected in parallel with the line, through the 40 decibel attenuator pad:

first to the instrument's input, then to the line. It listens without disturbing the link, and the spectrum analyser shows every carrier on it. The spectrum analyser covers ranges from 4 kilohertz up to 2.4 megahertz, with a zoom for the narrow bandwidths. Normal, peak, average or smoothed average, in decibels, dBm or dBm per hertz, down to minus 140 dBm per hertz. The built-in bridge measures longitudinal balance to ITUTO point 9,

return loss and impedance, and near-end crosstalk and loss. Noise is measured with the psophometric filter of ITUTO point 4 1, and impulse noise from 500 nanoseconds, over one second or up to 72 hours. For a cable or a voice channel, two instruments work together, one at each end. One is set as master and the other as slave, and they talk to each other over the line under test. Connect each one to its end of the pair. At the far end, choose slave and the connector.

At the near end, choose master, the frequency range and the impedance, and tick the measurements you want. When SLAVE READY appears, press start. Loss, noise, return loss, impedance, balance and crosstalk are measured in both directions. The master collects everything. The list of results appears first, and each line opens its graph, with a cursor to read any frequency.

Return loss, for instance, is shown for the master end and the slave end side by side. It keeps 100 test setups and 100 results. They move to a PC on a memory stick, with no driver to install, or over the USB cable with the PC software, which prints the results, exports them, and shows the spectrogram option over time. The nickel metal hydride battery gives about 8 hours, and recharges inside the instrument in less than 3 hours, from the mains adapter or from a 12 volt car socket.

The line inputs are protected up to 200 volts DC, and 60 volts of longitudinal voltage. It is used to commission and maintain power line carrier links and FDM systems, to check level, noise, carrier leak and crosstalk in voice channels, to characterise cables, and to hunt interference on a line in service. Test and measurement, from Amperis.