It’s always a good idea to verify that your scale factor and offset are right by plugging our second point into our completed equation, which in this case is (20, 100). Y = mx + b, where y = 0, x = 4, m = 6.25, and b is unknown. Now we will use the slope-intercept formula and the point (4, 0) to calculate the offset or b. We will use the two points (4, 0) and (20, 100) to calculate the scale factor or m. We will go about this example, in the same manner, we did the last one by first finding the scale factor and then plugging in a few numbers to calculate the offset. Īn output of 20mA represents a measurement of 100ftWC.These specifications again tell us two things:Īn output of 4mA represents a measurement of 0ftWC and We will still use the level Transmitter with a 0 to 100ftWC range, but this time we’ll use a 4 to 20mA output. Example 2Ĭonsidering that the 0 to 10V example is fairly simple, let’s move on to something more challenging like a 4 to 20mA output. Given that this arithmetical operation is valid, we have verified that our scale factor and offset are correct. It’s always a good idea to verify that your scale factor and offset are right by plugging our second point into our completed equation, which in this case is (10, 100). Y = mx + b, where y = 0, x = 0, m = 10, and b is unknown. Now we will use the slope-intercept formula and the point (0, 0) to calculate the offset or b. We will use the two points (0, 0) and (10, 100) to calculate the scale factor or m. M = (y 2-y 1) / (x 2-x 1)’ and choosing two points along the linear scale.Īfter the scale factor has been determined, we simply plug the value m back into the slope-intercept formula and use one of our points to calculate our offset. The factor m can be solved by using the slope formula It’s best to start with your scale factor, or m in the equation. Īn output of 10V represents a measurement of 100ftWC.These specifications tell us two things:Īn output of 0V represents a measurement of 0ftWC and Let’s consider the level Transmitter with a 0 to 100 ft WC range and 0 to 10V DC output. If you’re a bit rusty, have no fear, we’ll give you a couple of examples to freshen things up. ī is your y-intercept (also known as offset).Īs previously stated, linear scaling works best with linear voltage or current outputs in which the minimum and maximum outputs represent specific values along with the sensors range.M is your slope (also known as scale factor), and X is your input (whether it be voltages, milliamps, etc.), Y is your output (also known as engineering units value), It uses the old slope-intercept form ‘y = mx + b’ where The technique of linear scaling should remind you a few your days back in basic algebra. We’ll touch more on this in the next section. If your sensor has a 4 to 20mA output for a range of -40 to 100☌, it would be just as easy to scale the output into Fahrenheit by saying that the unit has a range of -40 to 212☏. It is also worth noting that when working with a sensor that has an analog output, the units specified for that sensor are not set in stone. In certain instances where formula-based scaling is not available, mapping can sometimes be used to predefine a table based on the formula needed and vice versa. Just to give a quick overview of these three methods and what they are best utilized for, we’ve put together a table below. These three techniques overlap a little bit as we will explain, but they are the primary methods used in the world of data acquisition. There are three techniques for scaling that we are going to cover here in this article: linear, mapping and formula.
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