Schwarzbeck ISN S8 Impedance Stabilisation Network

The ISN S8 can be used to measure the conducted voltage emissions of telecommunication and data processing equipment. It is designed to measure shielded cables with up to 4 wire pairs. It is based on IEC/CISPR 22 and the related national standards. The special circuitry and design is described in CISPR 22, CISPR 32 Annex G.11 and EN 55022 Annex D figure D.11 respectively. The ISN must provide sufficient decoupling from the equipment under test (EuT) to the auxiliary equipment (AE) which could be a communication device or a kind of load. The measured conducted voltage is coupled out to the BNC connector on top of the ISN S8. An EMI receiver or spectrum analyzer is most commonly used for a measuring instrument.

The ISN S8 can also be used in the other direction to inject conducted radio frequency disturbance into the shield of communication wires. This method is described in IEC/EN 61000-4-6. If the ISN S8 is used for injection it is also referred to as coupling decoupling network (CDN).

The ISN S8 is capable to provide 1000 MBit/s (Gigabit-Ethernet, 1000BASE-T). A cable of the suitable cable category is built in and is wired according to TIA-568A/B.

Application

The measurement is described in detail in CISPR 22, CISPR 32 and EN 55022.

The equipment under test must be connected to the EuT-port. The auxiliary equipment has to be connected to the AEport. The EMI-receiver or spectrum analyser has to be connected to the BNC port of the ISN S8 using a coaxial line.

Fixture lugs at the bottom plate of the ISN S8 allow to fix the device with screws to the cabin wall if wished.

As CISPR 22 defines the limits for conducted emissions in a 150 Ω system there is an 100 Ω resistor in series to the BNC connector. In combination with the 50 Ω input resistance of the measurement device a voltage division factor of 1:3 follows. In a logarithmic scale this is equal to 9.5 dB. The measured voltages across 50 Ω therefore has to be multiplied with 3 or in other words a correction of 9.5 dB must be added. This value of 9.5 dB is called the voltage division factor (VDF). This VDF is slightly frequency dependent. For very precise measurements it is recommended to take the exact frequency dependent VDF into account (see calibration certificate).

The shield or outer cable is defined as the common mode point for the EuT connector of ISN/CDN equipment. To be able to do a measurement (i.e. the impedance of the ISN or to normalize the voltage division factor) at this measuring point an adapter is needed.

This adapter can be purchased separately and is needed to connect the shield of the RJ45 socket to the measurement device. It is called “CA ISN S8” where the Usection can be attached to the shield of the RJ45 socket at the EuT part of the ISN and the 4 mm plug matches into the 50 Ω to 150 Ω adapter SR100-6W which can be purchased separately as well. It is given that when putting the ISN S8 and the SR100-6W together the normative distance of 30 mm between the front surfaces automatically is fulfilled.

 To enable you to connect your own measurement equipment the CA ISN S8 consists of two parts and can be taken apart very easily. A 4 mm plug provides the connection to the SR100-6W keeping the given distance.

If you want to use the ISN S8 as a CDN the use of the adapter “CA ISN S8”and the 50 Ω to 150 Ω adapter “SR100-6W” is mandatory. The measurement setup is described within the norm IEC/EN 61000- 4-6 picture 8c.

ISN Voltage Division Factor

ISN Impedance (Magnitude)