CLIXTRAB – testing options and operating principle Simplified maintenance activities, current measurement of the signal circuit, and interruption-free replacement CLIXTRAB includes several features that will make maintenance work much easier. The terminal block’s integrated knife disconnection can be used to disconnect the signal circuit without accessing the signal lines. This function is not just useful for maintenance work or troubleshooting, but also during startup. When the knife disconnection is opened, it is very easy to perform a measurement of the operating current or the insulation. Testing the lightning and surge protective devices at regular intervals is not only recommended, but indeed prescribed in many areas of application. Due to the surge protection plug, which can be removed and inserted without causing any interruption, the signal lines in the terminal block remain untouched. System availability is maintained while the plug is being tested or replaced. γ S1 N S1 N A 500 V MΩ γ S1 N Testing the surge protection plug using CHECKMASTER 2 Current loop measurement Dielectric test No impermissible influence on signal circuits due to the surge protection short-circuiting the signal voltage. The energy is discharged to ground and the sensitive electronics inside the signal box are protected (2). When the overvoltage pulse ends, the voltage drops back to the signal or operating voltage. This means that the varistor has a high resistance and is current-free (3) and the gas line is insulating (4). Under rated discharge conditions, this operation can be performed hundreds of times without any change in the insulating behavior or the overvoltage protection behavior. The circuit thus effectively limits overvoltages permanently and reliably rules out interference between signals and a short circuit to ground. Signal line A B Ground 1 2 3 4 Operating principle of the circuit illustrated by an equivalent circuit diagram The surge protection in signal technology systems must ensure impact-free behavior in terms of the signal lines. Surge protective devices consisting of the series connection of a metal oxide varistor (MOV) and gas discharge tube (GDT) guarantee this and reliably prevent leakage currents from exerting any impermissible influence on signals. In the diagram opposite, the signal voltage and the potential superimposed transient overvoltages are between the potentials A and B. The high or low-resistance states of the components (MOV and GDT) are symbolized by the switch positions (1–4). Under operating-voltage conditions, varistors are highly resistive and gas discharge tubes are insulating. Impermissible currents cannot flow (1). In the event of transient overvoltages between signal lines and to ground, for example due to a lightning strike, the highly insulating gas path of the GDT first becomes conductive. The overvoltage causes a current to flow through the varistor and is limited to the appropriate voltage protection level without 6 PHOENIX CONTACT