Guided wave radar level gauge having an explosion proof housing with an intrinsically safe output

A guided wave radar level gauge for determining the filling level of product in a tank, said gauge comprising:

• a housing providing explosion proof protection, and being electrically connected to a housing ground potential,
• an explosion proof first signal passage in said housing wall, said first signal passage configured to be connected to an external power supply,
• an explosion proof second signal passage in said housing wall, said second signal passage providing an intrinsically safe, IS, output,
• a resistor having a first terminal connected to the IS output and a second terminal connected to the housing ground potential,
• a transmission line probe connected to said IS output, said probe being adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product,
• wherein said housing encloses:
• radar level gauge, RLG, circuitry,
• a microwave unit connected to the IS output, said microwave unit configured to generate and transmit an microwave transmit signal ST and receive a microwave return signal SR reflected from the tank,
• said RLG circuitry and said microwave unit having a floating ground potential which is independent from said housing ground potential, and
• a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components,
• wherein the microwave unit includes:
• a pulse generator having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, and
• a differential receiver, having a first terminal connected to said IS output via said set of blocking capacitors, and a second terminal connected to said housing ground potential via said set of blocking capacitors, a voltage between said first and second terminals forming an input signal to said differential receiver.