Schwarzbeck NFCN 9731-100 Compensation Network

The primary function of the compensation network NFCN 9731-100 is to provide a serial compensation of the inductance of i.e. the HHS 5230 at operation frequencies of 16.666 Hz, 50 Hz, 60 Hz, 150 Hz und 180 Hz. These operation frequencies are stipulated by SAE J551-17 (Vehicle Electromagnetic Immunity – Power Line Magnetic Fields).

The NFCN 9731-100 provides two separate channels utilizing a shared control unit. Thus every single coil of the Helmholtz coil is powered by a separate amplifier. The current flowing through the coils can be checked using the built-in RMS-ampere-meters.

The compensation capacitor reduces the overall impedance of the series circuit consisting of the Helmholtz coil HHS 5230 and the compensation network NFCN 9731-100 at the applied operating frequency and allows currents up to 8 Arms at a generator voltage of less than 60 Vrms.

To protect the amplifier and the compensation network NFCN 9731-100 is equipped with a 10 A fuse.

An overvoltage protective circuit connects a damping resistor in parallel to the capacitor when exceeding the maximum operating voltage (at currents higher than 8 Arms)

The Helmholtz coil has to be connected (eventually using a load resistance in series) to the terminals “OUTPUT” and “COMMON”. The generator (output of the amplifier) has to be connected to the terminals “INPUT” and “COMMON”. The terminal “COMMON” may be grounded.

The wiring must not be done in different order. Otherwise the protection circuit does not work!

Block Diagram of the NFCN 9731-100

The signal level has to be increased slowly until the maximum current has been reached. Abrupt overload leads to voltage spikes. The protection circuit is too slow to prevent damage in case of abrupt overload.

The NFCN 9731 has to be controlled manually.

Measurement setup with a waveform generator, amplifiers, compensation network
(NFCN 9731-100) and Helmholtz coil (HHS 5230).

Operating:

Before putting the NFCN 9731-100 to operation you MUST set the voltage selector switch for the mains power to the correct value (115V/230V)! You can find the selector switch on the backside of the device on the left of the (IEC) socket.

1. Turn the volume regulator of the amplifiers to minimum.
2. Connect the devices to mains and switch them on.
3. Set the function generator to "SIGNAL OFF"
4. Adjust the level of the function generator to approx. 20…50 mV
5. Turn the volume regulators of both amplifiers to approx. 80% of the maximum level.
6. Set the rotary switch at the frontpanel of the NFCN 9731-100 to the required frequency.
7. Adjust the required frequency to the function generator and turn „SIGNAL ON“ on.
8. Slowly increase the signal level until one of the ampere-meters shows the wished current.
9. Use the volume regulator of the amplifier in the other circuit to balance the currents of both amplifiers.

Important! Switching capacitors is only allowed without applying any signal. Otherwise amplifiers and compensation networks will be damaged.

Note: If the overload protection circuit is active the LED “Overload” will light up and the compensation capacitor will be damped.

In this case:

1. Turn off the function generator immediately. (risk of overheating!).
2. Decrease the signal level
3. Turn off the NFCN 9731-100 for a moment and turn it back on again. The “Overload” LED won’t light up any longer and the compensation network will be ready to operate again.