November 2001Maintenance, Test & Measurement, Calibration
Instrumentation loop problems are time-consuming affairs for plant maintenance staff to deal with.
Most problems relate to isolation and ground faults, some of which present themselves intermittently or are hidden so deep in the plant wiring that tracing them becomes a full-time job.
Omniflex's new Omniterm range of DIN rail-mount loop isolators use advanced electronic techniques to address the common problems associated with instrumentation loops using several specialised new products:
* LPI loop isolator.
* LPx loop isolator.
* LPR loop repeater.
* LPS loop splitter.
The Omniterm LPI and LPX are current repeaters specifically designed to isolate instrument current loops from circulating ground currents that can cause system inaccuracies, or at worst, instrument failure. The current applied to the input is repeated on the isolated output, and the load present on the output is reflected back to the input. No separate power source is required.
These second-generation products utilise advanced electronic techniques to achieve high accuracy with minimum loop losses and zero field calibration.
The LPI is optimised for lowest volt drop over 4-20 mA, while the LPX is optimised for use with an extended current range from 0-50 mA and load impedances down to zero ohms.
The Omniterm LPR current loop repeater and Omniterm LPS current loop splitter products are specifically designed to create additional current loop signals from an existing current loop signal with minimal effect on the impedance of the existing loop.
The LPR has a single isolated output while the LPS has two isolated outputs.
These 24 V d.c. powered modules accept a 0-20 or 4-20 mA input and create 0-20 or 4-20 mA outputs. The output current loops repeat the input signal and are isolated from the input signal and 24 V d.c. power supply. Impedance changes on the output loops have no effect on the input loop. The module input is fully differential allowing the input to be connected anywhere in the input loop.
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