Filter technology

With more than 25 years in power generation and control electronics, we have developed specialised filters to keep installations running reliably. We have built filter solutions for the areas where we know faults occur, and where the market offers no product that protects the installation properly. We continually repair electronics that have been exposed to disturbances on the DC system. These faults are critical and usually lead to costly downtime.

DC filter

All electronics controlling a power plant run on DC. These installations are highly vulnerable to noise and surges. For effective noise and surge protection of electronic 12 V, 24 V, 48 V, 110 V and 220 V DC systems, we have developed filters that protect the installation.

Normally all electronic equipment connected to those voltages has a built-in DC/DC converter, stepping the voltage to +5 V, ±12 V and ±15 V. Reflected noise from DC/DC converters is often left unspecified, with requirements covering only radiated noise. The result is frequently noise on the DC distribution, which in turn causes problems for nearby DC/DC converters that may trigger on the noise pulses. Rectifiers and inverters also generate noise on the DC distribution.

A well-known problem when a thyristor or transistor fails in a rectifier is that the voltage rises, blowing the battery fuse. The battery's filtering effect is then lost, and both voltage and noise rise across the DC network. A further problem arises from surges caused by lightning. In such situations our filter engages and saves the equipment.

Our filters have been in service in DC installations for many years, and in that time no failure has been recorded in any installation where they are fitted. In one case 380 mV at 1.3 MHz was measured on the DC network; once the filters were commissioned, all noise disappeared. On heavy discharges the filter engages and disconnects the equipment it protects, reconnecting it after roughly 1–2 ms. On extreme surges the filter disconnects the connected equipment and raises an alarm.

The filters suit communications equipment, RTUs, water level gauges, data loggers and similar — often expensive equipment with long lead times. Prices range from about NOK 3,000 to about NOK 5,000 excluding VAT, FOB, depending on voltage level and load. Discounts apply for larger quantities.

Filters for measuring loops

It is a known problem that unexpected trips, incorrect readings and false detections occur because of noise entering measuring loops and being picked up by the analogue inputs of a control system. The fault occurs within a very short interval that the controller does not log, yet the process may come to a stop — which can have serious consequences. The sources are surges, transients, noise from circuit breakers opening and closing, motors starting and stopping, radio communication, mobile telephony and the like.

To overcome faults of this kind we have developed a filter series for the following applications:

Analogue filter
PT-100 filter
Ohm filter
RS-232 filter

Measurement data, DC filter model Allf 48-620

Signal to filter: −10 dB, 600 ohm, 0.775 V
Trigger point: 64 V
1500 W peak pulse capacity at 1.0 ms
Rating: 48 V / 6.2 A