All measuring devices used in critical applications must undergo calibration regularly. Calibration ensures they remain within the tolerances of their manufacturer’s requirements. For example, pressure gauges are frequently used instruments in the process sector. Thus, like other measurements, you must regularly calibrate pressure gauges, which ensures accuracy.
Three choices are available to make a pressure calibration. Examples are zero adjustments (1 point), zero and span adjustment (2 points), and multipoint adjustment. Often, a one-point calibration does not affect other measuring locations in the range. But is this true?
The most basic sort of calibration is one-point calibration. Sometimes, experts perform a one-point calibration to correct sensor offset problems. This is if you already scaled your sensor output to use measurement units. You can also use one-point calibration as a “drift check”. It can detect responsiveness and sensor performance decline variations. There are two instances where one-point calibration is suitable.
- The sensor is linear with the desired slope over the measurement range. You must calibrate only one point in the measurement range in this situation. You can adjust the offset if necessary. Many temperature sensors lend themselves well to one-point calibration.
- There is only one measuring point required. You don’t need to worry about the rest of the range if your application only requires single-level measurement. A temperature control system, for example, must continuously maintain the same temperature.
The pressure gauge calibration process can use one-point calibration. But you must review one or more calibration points, and the pressure gauge may require an upscale and downscale process. This depends on the specific pressure calibration requirements of the quality standards. The test points can be at zero and span or any combination. This two-point calibration follows the same steps as the one-point calibration. But it involves pressurizing the instrument to the top 20% of its range to get the second point reading. The span adjustment calculates a multiplier applied at each point along the observed pressure.
The standard has to be more precise than the DUT. The general rule is that it should be four times more accurate, although individual needs may differ.
Testing and calibration laboratories decide based on their experience, equipment, and the accuracy of the device under test (DUT). They also consider the required time. In most circumstances, they select one of three options, each of which is worth one point. A zero-point adjustment is the quickest and easiest technique to calibrate a transducer. It can provide an offset correction.
It employs a single point to calculate the difference between the reference value and the DUT reading. But the instrument may need pumping down in the vacuum range for an absolute transducer. It depends on the full span pressure. Because you adjusted all points, this calibration is ideal for transducers with a constant offset.
There are many techniques to calibrate a device. But, determining which device to use for each case to produce the best results can be difficult. Experts must use their knowledge, the type of calibration equipment available, and the device under test’s inaccuracy. Besides, they need to consider the time required to reach a decision.
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