Mitton Instruments | RFI Detector

Radio Frequency Interference (RFI) can be generated by gap discharge. This can occur on failing or polluted insulators, inadequate earth bonding and loosely connected HV line fittings. The HV breakdown wave-shape contains a broad frequency emission spectrum, modulated by 50 Hz. The frequencies generated range from audible to UHF.

Corona can also cause RFI but is far less likely in a well designed system, where conductors are sized to minimise the surface electric field strength and equipment is similarly designed to avoid corona.

HV gap discharge can easily become a source of RFI.

Since the gap discharge emissions are broad spectrum, it is possible to use a number of techniques to identify and locate noise sources. Specialised radio frequency equipment is available to detect RFI and the general location of the noise source can be found this way. However, the noise source can be located more directly when using ultrasonic detection. The advantages of ultrasonic detection are that audible background noise can be excluded and relatively accurate pinpointing of the noise source can be carried out.

Description

RFI from gap discharge often shows up as noise on a TV screen (particularly on the VHF channels) and on AM radio reception. RFI is particularly noticeable in regions where the TV or radio signal level is low (low signal to noise ratio).

The Ultrasonic Detector device can be used to pinpoint a source of RFI caused by gap discharge.

The device consists of a parabolic reflector which acts as a high gain ultrasonic antennae. Highly sensitive electronics circuitry decodes the ultrasonic signal and provides an audible and visual amplitude response to the user. The discharge is heard as a crackling sound, basically mimicking the actual discharge but in the audible spectrum.

The device can identify whether the noise is being generated at the top or bottom of the insulator.

The RFI Detector may also be used as a diagnostic tool. A general sweep of the HV hardware in a substation or on a line may identify noise. While not causing RFI, it may indicate imminent failure of an insulator or faulty hardware. Leakage across HV insulators may also cause hazardous voltages on associated LV earthing/grounding systems (eg dairy farm milking sheds).

Comes with Spark Generator for proving functionality