These definitions are provided from the Handbook of Electronic Weighting.Solution by area Acoustics Data Recording Flight/Space Testing Monitoring NVH Testing Electrical Power Testing Rotating Machinery Structural Dynamics Vehicle Testing Vibration Analysis Understanding the source of error can help increase accuracy when testing a load cell system. The following definitions are important determinants of the accuracy class of a load cell. The total error is determined by a number of varying factors, from temperature deviations to magnetic interference. This means the total error could be very high compared to a single increment of measurable weight. A load cell with a 0.1% combined error is accurate to a maximum error of ☐.1% of rated output. If a load cell experiences its maximum possible error, its minimum weight divisions be less reliable. The sum total of these errors is known as the combined error or maximum possible error. The maximum possible error is important when considering accurate division measurements. The sections below further define these terms. Unlike this section, it also covers resolution issues associated with digital signal converters.Īs seen in Figure 4, load cell specifications include error ranges for various causes such as non-linearity, hysteresis and creep. The next section explains the effects of amplifiers on the resolution of the overall weighing system. This is because they generally have internal amplifiers. Note that most displays are able to handle a small input signal such as this one. Therefore, the lowest weight detectable by a load cell is clearly not the only consideration in designing a weighing system. Likewise any tenth of an ounce increment of a larger weight will not display. The output voltage at this weight can be calculated as follows (since the relationship is linear): In other words, it can measure a weight as small as a tenth of an ounce (0.00625lbs). Let’s assume this load cell has 8000 divisions. Assume use of the recommended excitation of 10mv this means the load cell will output 10mV (1mV/V \(\times\) 10V) to the display when it bears the maximum of 50lbs. Otherwise, the measuring system will not give an accurate result.įor example, assume you have a scale whose internal load cell has a maximum load of 50lbs, a FSO of 1mV/V, and a recommended excitation voltage of 10V. The output of the load cell per smallest measurable unit of weight must therefore be greater than the input sensitivity of the display. (Figure 1 expresses this relationship.) Therefore, the smallest weight accurately measurable by the load cell is simply the maximum measuring range divided by the number of divisions.Ī display’s input sensitivity is the smallest signal, or change in signal, that it can detect. A load cell certified to adhere to one of these sets of requirements will have a marking indicating compliance this compliance implies adherence to a set of performance tolerances associated with each accuracy class.īecause the FSO reflects the range of voltages from zero to maximum load per volt of excitation power, one can assume that the number of divisions is also the number of increments from the minimum load to maximum load. The articles, Load Cell Classes: OIML Requirements and Load Cell Classes: NIST Requirements go into more depth with this topic. Requirements bodies such as OIML (internationally) and NIST (in the US) determine what is known as the accuracy class of a load cell by its number of divisions. The divisions are simply the number of increments a load cell’s full scale output (FSO) voltage can be divided into. One such specification is the number of divisions. The Most Important Data Sheet Specifications: Divisions and Full Scale OutputĮvery strain gauge load cell comes with a data sheet with a list of its specifications.
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