Radar level gauge (RLG) systems are in wide use for determining filling levels in tanks. An electromagnetic transmit signal is generated by a transceiver and propagated towards the surface of the product in the tank, and an electromagnetic reflection signal resulting from reflection of the transmit signal at the surface is received by the transceiver.
Based on the transmit signal and the reflection signal, the distance to the surface of the product can be determined.
Most radar level gauge systems on the market today are either so-called pulsed radar level gauge systems that determine the distance to the surface of the product in the tank based on the difference in time between transmission of a pulse and reception of its reflection at the surface of the product, or systems that determine the distance to the surface based on the frequency difference between a transmitted frequency-modulated signal and its reflection at the surface. The latter type of system is generally referred to as being of the FMCW (Frequency Modulated Continuous Wave) type.
Radar level gauging is generally performed either by means of non-contact measurement, whereby electromagnetic signals are radiated towards the product in the tank, or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe acting as a waveguide. The probe is generally arranged to extend vertically from the top towards the bottom of the tank.
For guided wave radar level gauge systems, different kinds of probes may be used, for example depending on the characteristics of the product in the tank, or the environment in the tank. In some radar level gauge systems, it may be desirable to use a probe comprising a first probe conductor and a second probe conductor. Spacers may be provided to control the positional relation between the first probe conductor and the second probe conductor, for example, to prevent contact between the first probe conductor and the second probe conductor.
Using conventional pulsed radar level gauge systems, in which the transmit signal has relatively low frequencies (such as about 0.1-1 GHz), for “normal” applications (excluding for example high temperature high pressure—HTHP applications), known spacer configurations exhibit relatively low reflections, and can therefore be used without noticably influencing the filling level measurements. Such known spacer configurations may, for example, include spacers made of a low-reflection material, for example PTFE. For HTHP applications, it may however not be possible (or at least not desirable) to use spacers made by PTFE, but ceramic spacers may be preferred. However, ceramic spacers exhibit stronger reflections, which may be detrimental to the measurement quality. An example of such ceramic spacers is described in US 2008/0078244.
Further, it may be desirable to use higher frequencies (such as 1-2 GHz) for the transmit signal, which may make the measurements significantly more sensitive to spacer reflections, so that even the use of spacers made of a low-reflection material (such as PTFE) may disturb the filling level measurements.
It would thus be desirable to provide an improved guided wave radar level gauge system with a probe comprising a first probe conductor and a second probe conductor, in particular a guided wave radar level gauge system with less disturbance from spacers arranged to control the positional relation between the first and second probe conductors.