Managing thermal expansion in liquid level measuring is a common issue in refinery and chemical applications that put level gauges outside the vessel or tank. In this configuration, the gauge is exposed to atmospheric conditions that may affect the temperature of the liquid in the gauge’s chamber.
Thermal expansion or contraction occurs depending, among other things, on how hot or cold the process liquid is and how far away the gauge is from the vessel. Good insulation minimizes the heat exchange. Components with steam or electric heat tracing also help. However, there still may be a significant change in temperature that can lead to differences in the level gauge’s reading and the tank’s actual liquid level.
Temperature Measurement in Liquid Level Indicators
WIKA has a complete solution for customers concerned about how differences in temperature in liquid level indicators may affect measurement of liquid levels. A temperature element can be attached to the magnetic level indicator or to the level chamber, making it possible to measure level and temperature at the same time. Using the data collected from this level, plus the temperature measurement, engineers can see how the different temperatures affect accuracy.
WIKA offers several electrical temperature measurement products. With its features and variety of options, the V-Pad® tubeskin thermocouple assembly is most commonly used with level gauges. The V-Pad is a flexible, insulated sheathed cable with mineral-insulated internal leads and a non-insulated point that can be welded to the surface of the wall of the external chamber. By welding the V-Pad to the chamber, the grounded measuring point becomes part of the surface and provides accurate measurements of the inner chamber temperature with a fast response time. Other ungrounded thermocouple designs cannot measure the inner chamber temperature to the same degree of accuracy (see drawings).
Skin temperature measurement on a radar bridle chamber
WIKA offers several sheath materials that are resistant to corrosion, high temperatures, hydrogen chloride, halogens, and sulfurous fuels, ensuring a sensor solution that will fit your application. The V-Pad thermocouple is also shock resistant and comes in several diameters.
Thermal expansion and contraction can compromise the accuracy of the data from your external liquid level gauge. Monitoring the temperature at the external chamber will help manage this problem. Contact WIKA’s product specialists for personalized assistance in finding the measurement solution that best suits your application.
Product mentioned in this article
• V-PAD® TC59-V tubeskin thermocouple