Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-08-03

Two common methods are used for calibrating float level gauges: the filling method and the weight suspension method. At the work site, the fluid filling method is generally used, with water serving as the standard fluid; in other words, water is used instead of the actual working fluid for calibration. Because the density of water at room temperature is known, and under normal temperature and pressure, water is a working fluid that is harmless to humans and relatively inexpensive. During calibration, based on the working density and scale of the actual medium being measured, the value is converted to the scale value applicable when calibrating with water, and a mark is made on the float. However, for floats used to verify working fluids with a density greater than that of water, it is not possible to calibrate the scale at 100%. Float level gauges are calibrated using the weight-hanging method, usually in a maintenance room. First, the appropriate weight is calculated based on the liquid level at different heights; weights and a weight plate are prepared, and the weight plate is hung at the position where the float is suspended. According to the calculated weight, weights are placed on the weight plate, and the output of the float level gauge is observed and recorded.

Irrigation calibration or weight hanging calibration

Irrigation calibration or weight hanging calibration

There are mainly two methods: the irrigation method and the weight-hanging method. ①On-site, the liquid calibration method is generally used; if the liquid to be measured is not water or alcohol, it can be calibrated using water or alcohol through density conversion. ②During maintenance, the weight-hanging calibration method can be used. During verification, remove the float, attach a weight plate, determine the values at the starting, middle, and ending points of the float, and conduct verification by adding weights.