Although differential and isolation amplifiers can eliminate some of the many possible sources of error and at least reduce their effects, only fiber-optic isolation amplifiers bring definite relief. Optical isolation of measuring circuits eliminates long measuring cables prone to electromagnetic interference, and potential differences of several hundred kilovolts become possible between measuring and recording circuits.
Applying fiber optic isolation with high impulse-current applications allows the ground potential to have dramatically transient changes without affecting the integrity of the signals captured and transmitted.

Besides these intrinsic advantages of optical transmission, the FOsystem by Power Diagnostix means simple integration into existing measuring systems and low electromagnetic interference even under difficult measuring conditions, thanks to the use of metal-clad and very compact transmitter equipment. In many cases, miniature transmitters designed on SMD principles can even be integrated into the measuring object. Transmitters are available in different variants, including, for instance, versions for adjustment to piezoelectric pressure transducers or displacement/position transducers. Besides these options, the units can be fitted with customer-specific circuits for adjustment to further sensors. We use a robust optical fiber type which features a very small influence of mechanical loads on its attenuation parameters. The plug-in receiver units are based on the 19-inch standard and can be combined to multi-channel measuring systems. Thanks to automatic adjustment of transmission links – even when transmitters and optical fibers are interchanged or replaced – this robust measuring system (over 400 measuring channels sold) is easy to handle.

System Variants

The FOsystem is a complete set of instruments for convenient fiber optic transmission of different types of analog signals from a variety of sensors. The FOsystem allows easy implementation of fiber optic transmission to solve noise, safety, and signal quality issues in high-voltage measuring environments and other demanding conditions.

The Power Diagnostix FOsystem comes in several basic variants, foreach of three signal types:

• FOS1 for analog transmission of analog signals from DC up to 10 MHz
• FOS2 for digital transmission of analog signals from DC up to 20 kHz
• FOS3 for pulsed digital transmission of slowly changing signals such as temperatures.
• FOS4 for digital transmission of analog signals from DC up to 65 MS/s

All versions consist of transmission units, receiver units, and sturdy fiber optic cables.

The fiber optic transmitter modules (FOT) are small individual modules for installation at sensors or signal sources. The fiber optic receiver modules (FOR) are mounted side-by-side in a 19-inch or half 19-inch rack.

Operation

The output signal of the signal source or sensor (for example, voltage, dynamic pressure, current, or partial discharge) is fed to the input of the FOT. The transmitter then either modulates the infrared light emitted by the transmitter diode according to the value of the input signal (amplitude modulation, FOS1), or digitizes the signal and transmits a digital telegram. This optical signal is transmitted via the fiber to the receiver, which converts it back to voltages for further processing.

The transmitter is installed in a castaluminum enclosure. The FOT is fitted with a NiMH-battery for a minimum operating time of twenty hours (FOT1 and 2), whereas the FOT3 offers up to two years of operation while sending a telegram every five seconds.