Measurement with guided microwaves in standpipes or bypass tubes
Sensors that operate according to the guided microwave principle (with rod or cable) represent the ideal measuring technique for use in bypass vessels. Due to the resulting coaxial configuration, measuring conditions are optimal. TDR is a measuring principle that is particularly suitable as a substitute for mechanical displacement systems used in bypass vessels. Under these operating conditions the upper dead band decreases to less than 100 mm, measurement accuracy improves considerably and the minimum DK value is reduced to approximately 1.6.
 
What is a DK value (dielectric constant)?
The DK value (εr) describes the electrical qualities of substances and represents an important parameter in guided microwave applications. Below a specific DK value, measurement is no longer possible because the transmitted signal is not sufficiently reflected. The threshold values of the different VEGAFLEX series 60 instruments can be found in the accompanying operator's manuals.
The DK value list can be found here:
Home » Services » List of measured products » Lists of dielectric constants

Implementation of rod segments
The use of segmented rods is possible if the installation conditions require it. For VEGAFLEX 62, rod components with a diameter of 16 mm are available. These can be used to construct a segmented rod waveguide. A 90° bend segment is also available.
 
Shortening or extending the rod or cable
An important advantage of the guided microwave principle is that the rod or cable can be adapted to the structural conditions. Modifications of the cable or rod must be done carefully to avoid discontinuities, since these can cause interfering signals. The instrument electronics also has to be informed, via the existing adjustment media e.g. PLICSCOM or PACTware/DTM, about the new length of the sensor, since this stored length value represents an essential component of the internal calculations. The instructions in the operator's manual must be observed.

Lateral mounting
In principle, a lateral installation of VEGAFLEX is also possible. But due to mechanical loads, this type of installation is only recommended for liquid applications. It is important that the specified minimum distance to the wall be taken into account. While the 6 mm rod of VEGAFLEX 61 can simply be bent on site, it is advisable to assemble the probe of VEGAFLEX 62 from segmented 16 mm rods. To allow optimal customization, straight segments (80 mm ... 1,000 mm) as well as an angled segment (90° with 150 mm leg length) are available.
Alternatively, a 6 mm cable with gravity weight can be fastened on the angled segment.

Recommendations for ammonia applications
The best results with applications in ammonia were achieved with instruments with a ceramic/graphite seal, because this material is diffusion-proof. Sensors in which elastomer seals are used are not suitable for these applications.

Interface measurement with VEGAFLEX 67
Beside its application for continuous level measurement, the guided microwave measuring principle was further developed for detection of liquid interfaces. In this technique, the microwave pulse guided along the cable or rod is reflected at the interface. A typical application is measurement of oil on water or solvents on water. The upper medium must not be conductive, and its DK value must be entered in VEGAFLEX 67. A valid rule of thumb: DK value of upper medium < 5. Layers (upper product) over approx. 100 mm thick are measurable. The dielectric constant of the lower product must be 10 higher than that of the upper product.
The DK value list can be found here:
Home » Services » List of measured products » Lists of dielectric constants

Can interface measurement with VEGAFLEX 67 also be carried out from below?
In principle, an interface measurement setup with VEGAFLEX 67 can be installed from below. The basic requirement is a lower medium that is not electrically conductive (DK value < 5). Only the distance to the interface between lower and upper medium is measured, not the total filling level. In this case, the requirements (as specified in the operator's manual/product information) on the upper medium apply here to the lower medium.

Are the electromagnetic waves of guided microwave devices dangerous?
According to the latest scientific research, the electromagnetic waves from VEGA radar level sensors are harmless. The sensors operate with a peak power output of under 0.5 mW, whereas a mobile telephone operates with 1 to 2 W of transmitting power!