The JCI 501 Lightning Warning System comprise two main parts: a Sensor Unit and a Base Unit. The Sensor Unit is mounted on open ground well away from nearby buildings and sources of physical pollution and electrical noise. The Unit comprises an electrostatic fieldmeter, suitable for continuous operation in adverse environmental conditions (a JCI 131), mounted on top of a 2m tall antenna which picks up radio noise signals (at 27kHz) and lightning impulse signals (over the band 2-200kHz). The Sensor Unit is cable connected (up to 100m) to the Base Unit which is mounted in a convenient nearby monitoring building. The Base Unit provides power supplies for the Sensor Unit and processes the signals for linkage to a nearby microcomputer which does all the analysis, display, risk interpretation and recording of observations.

Electric field: The atmospheric electric field is measured by an electrostatic fieldmeter acting as a potential probe a known height above ground level. This can be directly calibrated in local volts - so with the known probe height, the volts per metre is known. The advantage of this approach is simplicity of mounting, the avoidance of interference by ground level dust and debris and the enhancement of the effective sensitivity of the electric field measurement capability. The JCI 131 fieldmeter used for electric field measurement is based on well tried proprietary JCI design features. These provide high useable sensitivity and long operational life. Physical design features (large gaps and long insulation tracking paths) are based on previous experience of overcoming problems of operation in wet environments.

Radio noise and lightning impulse signals: These are picked up by the electrically isolated antenna tube which is also used to mount the fieldmeter above ground level. Radio noise signals at 27kHz and impulse signals within the 2 to 200kHz band indicate the level of lightning activity around. Low frequency signals travel with fairly low attenuation so existing lightning activity can be detected at large distances. These signals are processed on circuits mounted within the casing of the JCI 131 fieldmeter so all signals can pass through a single multicore cable to the Base Unit. The dynamic range of radio noise and impulse signal observations is extended using a logarithmic amplifier stage before precision signal rectification.

Base Unit and software: Measurement of the intensity and polarity of the electric field and of the amplitude of the radio noise and lightning impulse signals by the Sensor Unit are multiplexed into a 12 bit ADC so these signals can be communicated at 100 sets of readings each second to a nearby microcomputer for analysis, display and data recording. Software processing of signals from the Sensor Unit interprets these as observed atmospheric field values in volts per meter (or mV or mV for the radio signals) and these are used, displayed and stored as such. Software feedback to the Sensor Unit controls the setting of the sensitivity of the fieldmeter (4 decades) and of the radio noise and lightning impulse signals (1 decade) in addition to the logarithmic amplifier stage. It also applies signals to examine the operational health of each observation channel so early warning can be given of any loss of operational performance.

Processing of the signals from the Sensor Unit involves interpreting the 2-200kHz band observation in terms increases in amplitude of more than a set step change and outside a certain time frame that distinguishes single from separate lightning events. Cross comparisons are made of electric field strength above set threshold levels, radio noise intensity above a set threshold level and the frequency of occurrence of lightning events to determine whether there is no significant risk (green), an amber risk threat or a red alert threat. These alarm status levels are displayed by green, amber or red lights on the Base Unit and are also available for relaying to a remote repeat display.

Observations are displayed as graphs of electric field, radio noise and lightning impulse occurrence versus time with an additional trace showing operational health of the system and the interpreted lightning warning status. These observations are stored to the computer hard disc and opportunity provided for direct roll back for inspection of earlier records. Observations are stored at the same time to an external large capacity recording medium for long term back-up and separate analysis. Storage space can be minimised by averaging data over intervals where signals remain below user set levels.

Computer screen displays showing parallel presentations of electric field and radio observations with warning indications and alarm waring indications.

Sensor Unit:

Cable:

Base Unit:

Computer:

Software:

Operational health monitoring:

Test Unit: