Surge Protective Device
Surge Protective Devices (SPD) protects all types of sensors from Transient Overvoltage.
Transient overvoltage affecting sensors is typically due to lightning strikes where long, particularly horizontal wiring can be subject to these leading to destructive voltages at sensors.
Transient protection devices attempt to re-direct the energy in these transients by taking advantage of the differences between the transient waveform and the intended signal or power waveform.
It comprises five protected lines allowing for the protection of any four wire sensor including the screen.
Each line benefits from three stages of protection.
Stage 1 is a TVS (Transient Voltage Suppressor) Diode which protects against low level spikes and transients. This triggers and clamps the line to ground if the voltage exceeds 18 volts. The device is extremely fast and has a peak current rating of 56.6 amps.
Stage 2 is if the voltage exceeds 65 volts and protection is provided by a MOV (Metal Oxide Varistor) which, being connected in parallel to the TVS Diode, protects the Diode from excessive transients due to its higher current capacity of 250 amps and a power dissipation of 1.3 joules.
Stage 3 is for significant surges where each line is protected by a Gas Discharge Tube which trigger at a relatively high voltage of 230 volts and have a maximum discharge current of 15Ka.