Radio Frequency Interference Protection

Common Mode (Interference) Passband (-3 dB)

DC to 20 kHz

Differential Mode (Process Signal) Passband (-3 dB)

DC to 45 kHz

Attenuation

Greater than 50 dB from 100 kHz to 100 MHz

Transient Protection

Maximum transient voltage output

FL5:

+/-10 Volts

FL20:

+/- 40 Volts

Response Time

10 nanoseconds

Impulse Discharge Current

5 kA (8/20 microseconds)

Maximun Operating Line Voltage

FL5:

+/- 5 Volts

FL20:

+/- 20 Volts

Maximum Operating Line Current

2 Amps

Line Loop Resistance

0.2 Ohms

Line Resistance To Ground (each leg)

1 MOhm

Dimensions

Width 22.5mm; Height 75mm; Depth on rail: Sym 102mm; Asym 107mm

Design Features

A symmetrical T filter configuration is employed to keep earth return currents to a minimum and reduce the effects of common impedance coupling on the performance of the filter. The filter inductors employed are of double wound ring core construction maximising attenuation of common mode interference signals independently of line current while maintaining the differential control signal bandwidth.

At the input of the filter high capacity surge arrestors are used as a first stage voltage clamp from each signal line to ground. A second stage is incorporated into the filter using fast semiconductor transient suppressors which clamp the voltage with respect to ground and between the signal lines to control both common mode and differential transients.

Connection Details

The signal cable should be of screened construction for best performance. The incomming signal pair connect to terminals E and F. In general, the screen should only be grounded at one end at connection D. If the screen is already grounded at the source, the RF screen ground on terminal A is provided for termination. This is a capacitively coupled earth preventing possible high currents flowing in the screen at supply frequencies. The output to the equipment port (which may be a signal input or output) is taken from terminals H and G with the screen connected to J. The screen should be unterminated at the equipment connection.
Terminals C and K are the main system earth and at least one of them should be connected directly to the system star earth with as short as possible length (300mm) of 2.5mm cross section stranded copper wire. This must be a safety earth.
Input and output cable runs should be kept separate to avoid stray coupling degrading the overall rejection performance. If more than one equipment port is connected to the unit ensure continuity of the screen.
All terminations have provision to accept terminal markers to suit specific installations.

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