Precision Lightning Sensor
Precision Lightning Sensor (PLS™)
The latest generation of TOA's Precision Lightning Sensor (PLS) is shown in the photograph above. The PLS has enormous advantages over other lightning sensor designs, in particular those based on magnetic direction finding (MDF) which suffer from significant site introduced errors and consequent high siting coasts.
The PLS can be installed on existing structures, towers, and buildings where access to electric power and communications is readily at hand. The PLS is also extremely adaptable in terms of communications, it's design allows it to transmit its data by telephone, network, internet, or radio as is deemed best suited to the requirement.
Precision Lightning Sensors (PLS™) used by TOA do not monitor magnetic field signals as do Direction Finding (MDF) based sensors, therefore TOA sensors have liberal siting criteria.
The PLS™ is unaffected by buried or overhead powerlines, and other sources of electromagnetic field anomalies which make site selection and preparation such a costly matter for users of MDF-based lightning location systems.
The TOA PLS™ Lightning Detection Subsystem offered herewith consists of the following elements:
a. Stroke Antenna - Outdoors
b. GPS Receiver Antenna - Outdoors
c. PLS™ Receiver Module - Indoors
PLS Overview
The detector part of the sensor is a broadband receiver. This picks up a substantial amount of the lightning energy that allows the system to distinguish between ground lightning and cloud lightning. With a broadband detector the different characteristics of ground strokes and cloud strokes can be identified. This allows classification of the detected strokes by the PLS sensors.
In a time-of-arrival based system, timing is an important part of the receiver. The PLS receiver uses commercial GPS timing as a reference. The sensor uses a high frequency timing source that makes the timing more stable, accurate and increases the resolution. The timing is constantly monitored and corrected. This results in more accurate lightning locations.
An onboard processor handles communications and monitors the over-all operation of the sensor. It keeps track of the timing system.
The sensor is designed for remote configuration of the hardware. This is accomplished using Field Programmable Gate Array (FPGA) technology. This allows remote configuration of the hardware using bit patterns. Upgrades can be performed without visiting the site.
The sensor is also designed for remote configuration of the software. Software is downloadable over the communications link. The programs are stored in non-volatile memory on the board. It is not affected by power glitches, losses, or outages. Again, upgrades can be performed without visiting the site.
Flexible Communications The sensor supports various communications methods. It has an onboard 10-Base-T network controller that allows TPC/IP communications over a network. There is also a standard serial communication circuit for modem or satellite communications.
Rugged & Reliable Antenna System The PLS™ has two antennas. The first is an active GPS antenna used for the timing reference. The second is used for stroke detection and is typically ~ 1 meter in length, with the precise length determined by network performance requirements. Both antennas are small and light weight, have a small wind resistance, and are easily mounted on existing structures without requirements of extensive civil works. They are designed for easy maintenance; and since there are no sensitive electronics mounted outdoors, site selection is simplified and reliability enhanced. A typical installation of the outdoor antennas and indoor PLS™ electronics can be viewed in the images which follow.
Comprehensive Diagnostic Capabilities Built-in diagnostics monitor the system and allow remote diagnostics using RSD as long as the communications software is running. Sensitivity and other system settings, are user adjustable with RSD, depending upon the needs of system.
Performance Verification The characteristics of ground lightning are well known, and the PLS™ sensors are programmed to look for these characteristics. The sensors discriminate ground strokes by monitoring the characteristics of the radiated energy at the lower frequencies. The engineers of TOA Systems, Inc. as well as many other scientists, engineers and operators around the world have measured the detection efficiency and location accuracy of time-of-arrival lightning location systems. To achieve this understanding one can monitor high towers, which can receive many lightning strikes. Thorough investigations on three 1000-foot and larger towers in Florida were performed, and accuracy and consistency were validated.
Cloud Lightning Detection Cloud lightning (CLD)
generates much higher short-term energy at higher frequencies than cloud-ground strokes, which the sensor will identify. The precise timing of a cloud pulse of a certain magnitude will allow the very accurate location of that pulse using time-of-arrival mathematics. Due to their very high sensitivity, PLS™ sensors have no problem detecting cloud stroke signatures; but because of the comparatively weaker peak voltages received at the antenna and the effects of propagation delays over longer distances, signal strength thresholds will also be lower than for ground strokes.