Load Cells for your scales are in stock and ready to ship from 1800scales.com. We have a wide range of stock load cells for your weighing needs from top brands like Rice Lake, Cardinal, Vishay Sensortronics, Celtron, HBM, Revere Transducers, Transcell Technology, & Tedea Huntleigh. We ship these strain gauge load cells out everyday from our warehouses across the country. If you need a loadcell quickly, give us a try. We also offer many interchangeable load cells in case you're having a hard time finding a particular make or model number directly proportional.
Whether you’re looking for a load cell for a unique force applied application or have one that needs to be replaced, there is a likely a choice to meet your requirements. We can help you select the best load cell for your application, from tank and hopper weighing to bulk material weighing and everything else.
Aluminum load cells are used primarily in single-point, low-capacity applications. When compared to alloy steel cells of comparable capacities, aluminum load cells have relatively thick web sections. This is necessary to provide the proper amount of deflection in the element at capacity. Machining costs are usually lower on aluminum elements.
Load cells manufactured from alloy steel elements are some of the most popular cells used today. The value is better for alloy steel elements compared to either aluminum or stainless steel designs. This type of steel can be consistently manufactured to specifications, which means that minor load cell design changes don’t have to be made every time a new lot or steel vendor is selected.
Stainless steel load cells are made from the best overall performance qualities that allow for cell to perform at peak levels. They can be fitted with hermetically sealed web cavities, making them an ideal choice for corrosive, high-moisture applications. This is the best material to use in any application that requires extra protection because of the metal’s environmental resistance properties.
How does your existing load cell look? If it is covered with rust, corroded or badly oxidized on its exterior, corrosion has likely worked its way into the strain gauge area. If the general and physical condition has a good appearance, then you likely need to look at specifics: sealing areas, the element itself and the cable. In most load cells, areas of the load cell are sealed to protect the internal components from contamination by water and chemicals. To see if any seals have been degraded, look closely at the strain gauge seals.
As you know from the ohm's law relationship between voltage current and resistance, the usual value for a 1% shift in zero balance is 0.3 millivolt, assuming 10 volts excitation on a three millivolt per volt output load cell. To determine your application’s zero shift, multiply the excitation volts supplied by your indicator by the millivolt per volt rating of your load cell. When performing your field test, remember that load cells can shift up to 10% of full scale output and still function correctly. If your test strain gauges display a shift under 10%, you may have another problem with your suspect cell, meaning further testing is required. If the test cell displays a shift greater than 10%, it is likely it has been physically distorted and should be replaced.
However, even if the overall output resistance test is within normal specifications, you may still have a damaged load cell. Often when a load cell is damaged by overload or shock load, opposite pairs of resistors will be deformed by the applied force equally, but in opposite directions. The only way to determine this is to test each individual leg of the bridge. The Wheatstone Bridge diagram illustrates a load cell resistance bridge and shows the test procedure and results of a sample cell damaged in such a manner.
Regarding electrical resistance, if a load cell is still not performing to specifications, check for electrical leakage or shorts. Leakage is nearly always caused by water contamination within the load cell or cable, or by a damaged or cut cable. Electrical shorting caused by water is usually first detected by an indicator readout that is always unstable, as if the scale were constantly "in motion." This commonly occurs when cheaper environmentally protected load cells designed for normal non-washdown environments are used instead of the more expensive hermetically sealed load cells which could have stood up better to washdown applications.
To deter electrical leakage problems, test resistance to ground with a low-voltage megohmmeter. Use caution—a high-voltage meter that puts more than 50 volts of direct current into the cell may damage the strain gauges. If the shield is tied to the case, twist all four leads together and test between them and the load cell metal body. If the shield is not tied to the case, twist all four leads together with the shield wire and test between them and the body. If the result is not over 5,000 megohms, current is leaking to the body somewhere.
When your load cell(s) are connected the summing card, signal trimming is the most common type of trimming because it is the easiest to use. Compatible with virtually all indicators and relatively immune to temperature and vibration problems, signal trimming is gaining popularity for all installations. It involves adding a relatively high parallel resistance between the signal leads of each load cell. The added parallel resistance creates a "leakage path" that shunts some of the available load cell signal away from the indicator.