A case study on the commissioning and troubleshooting of E+H guided-wave radar level gauges for technical upgrades

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During the calibration of the E+H fm40 guided-wave radar level gauge used in a horizontal tank as part of a technical upgrade, the screen did not display any information. The cover was removed to check the load voltage, which was close to 0 volts. When the wires were disconnected, the voltage was around 17 volts. Someone was sent to the DCS room to check together with the DCS system; there was indeed an output, but when a short circuit was created, no signal was detected. When the connection was broken, the no-load voltage was close to 0 volts, showing a correlation with the presence or absence of a signal. Inform DCS to check the location number of the junction box; it is stated that there is no data sheet for this level gauge, and the location number of the on-site junction box is unknown. There was no other option; I followed the wiring tube of the level gauge to locate the junction box, opened it, disconnected the wires, and inspected the cable. The cable running from the junction box to the level gauge appeared to be in good condition. I also checked the main cable coming from the DCS, and its conductivity was normal as well, with a normal no-load voltage. There were signs of oxidation at the wire ends; after dealing with that, I reconnected the wires, but still no display occurred. When I measured the voltage at the connection terminals after reconnection, it was still close to 0 volts. . . It’s the same as before. There was no other option; the main cable and the field cable were directly shorted together in corresponding positive and negative pairs, and both the display and voltage values were normal. Remove the stitches, loosen the clamps at both ends of the wiring strip, and take off the wiring strip. . . This junction box is made of aluminum, and it must have been exposed to water before; the components used for the technical modification were the spare wiring strips that were available, which contained a large amount of metal shavings such as aluminum powder. . . Manual purging and cleaning. . “It’s better to purge with an air source.” After reinstalling and resetting, everything is normal, OK. .