1/2018 | MONITOR | 27 Measurement of capacitively coupled systems A noteworthy feature of the isoHR685 is its ability to monitor long, parallel and capacitively coupled cables. A type of synchronisa- tion enables interference from neighbouring monitoring devices to be suppressed and filtered out. Cables over 100 km in length, and in which various unearthed power supplies (IT systems) are routed can now be monitored. It doesn’t matter whether the IT system is implemented as an AC, a DC or an AC/DC system. The AMP measuring method used can be used in all systems and it also determines the system leakage capacitance. In long cables such as those encountered in the oil and gas industry, e.g. to sup- ply oil production facilities installed on the sea bed, energy lines, hydraulic lines and communication lines are grouped together in what is known as an umbilical cable. Since these cables are cus- tom-made, since they have long delivery times and since they are also hugely expensive, it is of great benefit to interpret at an early stage the trend of the insulation level developing within them and to take appropriate remedial action when necessary. Fault analysis Customers often have the problem that sudden and transient insulation faults occur in their installations. These faults are reported via a relay point. It is then often difficult to make decisions concerning maintenance measures if the avail- able information only refers to this switch con- tact. Troubleshooting is difficult and time-con- suming in the absence of additional measures. On the other hand a targeted troubleshooting process and plant analysis can be accom- plished with the isoHR685 via an integrated his- tory memory with real-time clock. Each reported insulation fault is deposited in a history memory with accurate time stamps showing when faults occur and disappear. This makes it possible to establish which consumer or which system part was switched on, switched off or switched over and at what time. Defective or faulty system parts can then be identified without switching system parts off (avoidance of failures). Communication State-of-the-art technology involves the use of programmable logic controllers (PLCs) con- trolling and monitoring plants. The Modbus TCP interface which is integrated into the isoHR685 allows straightforward communication with avail- able PLC and control systems. All measured val- ues can be read and displayed via this interface in the form of trend graphs . Following a security clearance it is possible to configure all parame- ters of the device externally and to reset or test the device via Modbus TCP. “A noteworthy feature of the isoHR685 is its ability to monitor long, parallel and capacitively coupled cables.”