Installing the transmitter directly on the steel pipe in the tank
To prevent openings at the tank, and therefore potential leak problems, the pressure transmitters are usually introduced into the tank suspended by a cable from above through special openings and immersed in the medium to be measured (see figure). Because both the measuring probe as well as the cable are in the tank and hang freely, there are mainly two aspects, in addition to media compatibility (e.g. in the case of aggressive media), which measure another level than intended as a result. There is a risk that the cable sheath will be damaged during installation or operation, allowing fluid to get into the transmitter between the cable sheath and cable wires, resulting in electronic failure within a very short time. The penetration of fluid into the pressure transmitter is the most frequent cause of failure in immersed level probes.
The transmitters are often provided with an additional weight to prevent them from being pulled along with the flow or are fastened to the tank wall. Special cable protection is rarely realized. Trafag offers an especially clever solution: There is an interface on the pressure transmitter for a special Serto® screw joint. With this metallic-sealing screw joint, a simple metal pipe can be pushed over the cable and screwed bluntly with the adapter included in delivery (see figure). Of course, this solution is somewhat more expensive than a bare cable, but it offers a wide range of advantages:
- The stainless steel pipe optimally protects the cable from damage, including to the cable sheath.
- The steel pipe is firmly mounted to the upper part of the tank and fixes the immersed transmitter in its position, independent of any flows.
- The entire upper part of the transmitter, including the cable, is insulated from the medium with the stainless steel pipe and leak-tight screw joint. Especially in the case of aggressive media or such where one is not sure of the effective composition, such as waste water, one can then do without an expensive, media-compatible cable and select the most cost-effective cable material.
- In the case of very deep tanks, the pipe can be welded in the lower area of the tank, saving a lot of cable length and wiring work (from the upper section of the tank).
- Optimal equipotential bonding is ensured by the metallic connection of the sensor housing with the tank, which protects the transmitter even better, with regard to EMC as well as with regard to electrochemical corrosion. The adapter system has been tried and tested for years and is safe and easy to install - all you need is a metal saw, a file and an openend wrench. It is also corrosion- and ageing-resistant thanks to the metallic seal. All necessary parts except for the steel pipe and the assembly tools are included directly in delivery with the Trafag pressure transmitter.
These two examples will show how often unforeseen options open up for well-known problems thanks to innovative approaches.