There are several ways in which a device can be calibrated, which can be daunting and hard to understand.
Calibration labs use their experience, calibration equipment, the inaccuracy of the device under test (DUT), and the time required to decide.
In most cases, they choose one of three options:
- Zero or span adjustment (one point)
- Zero and span adjustment (two points)
- A multipoint adjustment (three to eleven points)
The fastest calibration of the three is using a zero-point adjustment. They typically do this in the lower 20% of the transducer range. To create an offset correction, it uses a single point to calculate the difference between the reference value and the DUT reading.
As simple as venting the device into the atmosphere, both pressure and reference ports for a gauge transducer. Zeroing an absolute transducer may require the instrument to be pumped down in the vacuum range. This depends on the entire span pressure.
One-point calibration is ideal for transducers with a constant offset because the adjustment applies to all the points across the range.
Another standard procedure is a zero and span adjustment. This two-point calibration uses the same process as the one-point. Still, it requires pressurizing the instrument to the top 20% of the range to get the span or second point reading. The span adjustment creates a multiplier factored in at every point within the measured pressure.
They do this type of calibration on transducers with zero error and a linear drift throughout the range.
While it is normal for transducers to have a zero shift or span drift, occasionally, it will have inconsistent linearity throughout the range. Sometimes, it will have no offset detected at the zero or span point. However, it will still have errors at various points throughout the range. It will need a multipoint adjustment for instruments with this type of behavior.
The calibrator can use anywhere from three to eleven reference points to perform this type of adjustment. We can think of each set of points as individual 2-point calibrations. The multipoint calibration always gives the best results. However, it requires the most time to perform.
How to Know What Calibration It Needs?
It is only possible to know the exact type of calibration required once an as-found calibration is performed on an instrument. This often includes a zero-point adjustment as part of the process. Once this is done, a calibration technician will understand which type of procedure needs to be performed to get the instrument back in service.
Understanding the differences between the calibration types plays a vital role in the efficiency of a calibration lab. SRP control systems ltd is your local one-stop lab with over 40 years of experience in the industry for your calibration needs.