Schwarzbeck NNBM 8124 Single Path Vehicle AMN (LISN)

Interference voltage measurements acc. to CISPR 25 or MIL-STD-461F

Mains is connected at the back side. The 1 µF capacitor must be switched on to filter external disturbance and to provide best isolation values. The DuT is connected to the front panel. The disturbance voltage is coupled to the BNC connector where it can be measured with an EMI receiver. The switch at the front panel must be switched to “Measure”. In most cases one AMN for each line (e.g. + and -) must be used. In this case one NNBM 8124 must be connected with its red terminals along the + line and another one also with its red terminals along the – line. The LISN of the line that is being measured is switched to “Measure”, the other one is terminated by switching the front panel switch to “50 Ohm termination”. The RF-reference ground must be connected to the GND-terminals.

The 4 mm laboratory jacks at front- and back panel and the flat aluminium feet are electrically connected to the GNDterminals.

Immunity tests with bulk current injection (BCI-tests):
NNBM 8124 can be used for bulk current injection tests together with suitable current injection clamps. The maximum continuous power rating is 50 W at the EuT-terminals. With a continuous power input of 50 W the LISN housing heats up to approx. 60° C at the front panel. The operator must be aware of high temperature. A sufficient air-circulation must be provided to avoid overheating of the LISN. Do not cover the LISN! The top and bottom hole-plates must not be covered to provide good air circulation. A light smell of coating and insulating material may appear in the first hours of operation, take care for not inhaling the emitted gas. The smell will disappear after some hours of operation under high temperature.

During bulk current injection tests danger may arise by high field strengths and temperatures (fire hazard!), therefore these tests must be made by qualified personnel only! The relevant safety precautions must be considered!

For BCI-tests the switch position "50 Ohm Termination" is used. The power injected at the EuT-terminals is converted to heat inside the 50 Ohm / 50 W resistors. Please note: The switch position "Measurement" guides the injected RF-power directly from the EuT-terminals to the BNC-output without any attenuation. Eventually connected RF-measuring equipment may be damaged!

Transient measurements (ISO 7637-2)
The NNBM 8124 can be used to measure transients according to ISO 7637-2. The 1 µF capacitor on the mains side could short transients and must be switched off for this purpose.

Notice:
As the circuitry is according to CISPR 16 there are high ground currents. It is normally not possible to use a LISN on power lines with ground current safety switches (They disconnect power due to excessive ground current). Either a special power line outlet without ground current safety switch must be installed (warning label required!), or an isolating power line transformer 1:1must be used.

In any case, ground-connect LISN before connecting to power line. Precise safety instructions must be provided to any user of the LISN.

Simplified circuitry of the NNBM 8124

Application:

The main application of the unsymmetrical single path AMN (artificial mains network) NNBM 8124 is the measurement of interference voltage in vehicles, aircrafts and ships in the HF-VHF range 0.1 – 150 MHz. The NNBM 8124 can also be used for bulk current injection (BCI) testing or for transient measurements according to ISO 7637-2. The impedance characteristic is realized according to CISPR 16/25 and MIL-STD-461F (5µH + 1 Ohm) || 50 Ohm.

The continuous current rating is 70 A, for short time more than 100 A are possible. The EuT is connected to the wing terminals at the front panel. The mains terminals are on the backside.