Seeking help with weighing issues in Toledo
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The company currently has 10 tank weighing systems, each consisting of 4 SLB415 weighing modules (with a maximum weighing capacity of 2.2 tons per module), one IND331 indicator, which transmits 4-20mA signals to the DCS. The measurement range is 0-2500 kilograms, and these systems have been in use for 1 year and 7 months. During normal use, the weight decreases gradually; once it reaches the lower limit, material is added to bring it back up to the upper limit, and this cycle repeats. In recent days, one system has been experiencing the following issue: during use, its weight suddenly increases or decreases by about ten kilograms, and this persists for anywhere from a few minutes to several dozen minutes before returning to normal (such fluctuations occur even when the system is not in use). The frequency of these occurrences varies; sometimes there are 6 or 7 instances per day, while at other times there are only 1 or 2 instances per day. Upon on-site inspection, it was found that there was a problem with the weight at the IND331 header (in other words, the weight displayed on site was fluctuating); therefore, issues between the header and the DCS were ruled out. I checked the 4 sensors, and their impedances were all normal. I would like to ask the experts here – where could the problem lie? How should one make a judgment?
I would like to ask what the sensitivity of your sensor module is. To specifically determine the quality of a sensor, in addition to impedance, it is important to measure the sensor’s signal voltage in order to assess any imbalance in the module. If the deviation of a certain signal voltage is large, it indicates that this module needs adjustment for balance. Next is the inspection of the soft connections of the equipment.
The repeatability is poor; the zero-point signal of the response module lacks reproducibility. The instrument cannot automatically adjust itself to the zero range; in most cases, this is due to fluctuations in the signal voltage of a certain sensor.
I’ve replaced both the table header and the wiring panel, but the problem still persists
The signal voltages at 0 weight are 1.87, 1.77, 1.91, and 2.22 respectively
First, check whether there is a problem with the flexible connection that might be interfering with the weighing process. Second, check if the guide bolts of the tank are in contact with the seat of the tank. Third, the voltage values you have still differ quite significantly; you can recalibrate them using shims； Fourth, under the condition that everything else is normal, recalibrate the empty tank: one method is zero calibration, another is calibration using a weight, or it can be done through an internal weight-free calibration process.
The main thing to check is whether the load is distributed evenly across the four weighing sensors, in other words, whether the tank is shifted； Is the load cell in a free state, with no contact with any equipment and subject to no lateral shear forces?
In cases like this, it is mostly caused by interference; check if there are any sources of interference in the vicinity
Your 2.2 millivolts and 1.7 millivolts are asymmetric. The balance is poor. How are your soft links? Mettler offers shims in different sizes (made of stainless steel).
The signal voltage at the four corners is controlled at around 0.2. The Wheatstone bridge on the signal board can be adjusted for processing