Honeywell SMV 3000 user manual Resetting Calibration, About Reset Accuracy for PV1 and PV2

10.5Resetting Calibration

About Reset Accuracy for PV1 and PV2

You can erase incorrect PV1 and/or PV2 calibration data by resetting the data to default values. The default values return the transmitter calibration to the original factory “characterization” values for the existing LRV and URV. Characterization calculates a mathematical model of the performance of the transmitter’s sensors and then stores that data in the transmitter’s memory. Note that this is not the “final calibration” which is done at the end of the process against the ordered range.

While resetting the calibration will return the transmitter to a close approximation of the previous calibration using its stored characterization data, the accuracy of the “reset” transmitter will be lower than the specified final calibrated accuracy. The calibration is not exact since the transmitter mounting angle may be different than the factory mounting angle and time drift may have occurred since the factory characterization. This means that the transmitter is calculating its output based on the characterization equation alone without any compensation for the small residual errors of zero offset and span correction.

For example, a typical zero offset correction is less than 0.1 inH2O for a 400 inH2O range and a typical span correction is less than 0.2% regardless of the range (down to the point where specification turndown begins). The typical performance of a 400 inH2O transmitter after a calibration reset (or a “Corrects Reset” as it is often called) can be expressed as:

	0.1 inH2O	
Accuracy = 0.2% + 		 • 100%
	Span inH2O 

By correcting the zero input, the typical performance will be 0.2% or better.

For other transmitter ranges, the initial zero offset will be scaled by the ratio of the Upper Range Limit (URL) to 400 inH2O at 39.2 °F (4 °C). Thus, for a 100 psi range, the initial zero offset can be expressed by:

• 2768 inH2O =

0.1 inH2O0.7 inH2O or 0.025 psi 400 inH2O

Note that these are typical values and they may vary. However, our patented characterization method includes several techniques that help to ensure that this level of performance can be achieved.

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