1/201 8 | MONITOR | 19 The isoHV1685D-425 extends the device series iso1685 beyond the voltage limits of the low-voltage sector. In particular, it can be used whenever unearthed power supplies (IT systems) with voltages of up to 3(N) AC, AC 2000 V/DC 3000 V are to be monitored, on which system leakage capacitances of 150 µF will not be exceeded and where the use of a current transformer prompts the expectation of substantial voltage components with frequencies in the range of 0.1 Hz to 460 Hz. The insulation resistance levels of unearthed AC, AC/DC and DC power supplies (IT systems) are monitored in accordance with DIN EN 61557-8 (VDE0413-8) and IEC 61557-8. Measurements can be conducted safely and reliably, even under the influence of connected current transformers. The separate supply voltage makes it possible to monitor these in a shut down system. The devices can be operated with the DC 24 V power supply that is commonly available in switch cabinets. Two separately adjustable response values/alarm relays make it possible to issue messages at an early stage, long before the system reaches a critical con- dition. If the insulation resistance exceeds the release value (response value plus hysteresis), the alarm relays switch back to the initial position again. The high-resolution graphic LC display can show the exist- ing measured values as well as the alarm messages. Parameters are also assigned to the device via the display and the control buttons on the front panel as well as via the RS-485 interface. The device combination of the ISOMETER ® IRDH 275B-1 insulation monitoring device and the AGH507S coupling device may constitute an alternative with interesting technical properties for the monitoring of furnace applications in purely AC or 3AC IT systems, without galvanically coupled DC circuits. This device combination can be used at up to AC 2500 V in the frequency range of 50 to 3000 Hz. Despite the high nominal voltage range - after calibration - response values of a few multiples of 10 Ohms can be set. Dipl.-Ing. Dieter Hackl, Standards & Innovation However, the isoHV1685D-425 offers the operator important benefits compared to the older solutions for purely AC IT systems available on the market, such as the ISOMETER ® IRDH275B-1 in conjunction with the AGH507S: • Optimised monitoring of furnace applications in AC/DC IT systems that use frequency inverters • Coverage of the lower medium-voltage range without additional coupling devices • Response values also in the lower 100 Ohm range with greatly improved precision • Plug-in terminals provide durably safe and quick wiring • Password protection to prevent unauthorised parameter changes • RS-485 interface for data transmission. INFO More information: