How to artificially improve the accuracy within the accuracy range of the instrument

The accuracy of the watch itself is certain, so it is required to use equipment with the same accuracy as possible in the supporting equipment or instruments. For example, the recommended inner diameter and length of piping should be adopted according to the manufacturer's recommendations, measures should be taken to avoid stress during installation and reduce electromagnetic field interference. The instrument will be calibrated regularly in the future. If you have any questions about measurement, you can follow up and communicate at any time.

Flowmeter accuracy is tested and calibrated at the manufacturer. There are also differences between on-site installation conditions and the factory. Generally, the actual measurement accuracy of the factory is higher than the accuracy marked on the factory certificate.

When calibrating the flow meter, try to adjust the indication errors of the two meters to be consistent. If the error cannot be adjusted, replace it with one that can be adjusted.

There is a bad idea that requires instrument suppliers to provide products with consistent deviation directions, such as positive deviations or negative deviations. . . On the other hand, the wool comes from the sheep, so the various additional costs incurred by the supplier still have to be borne by the owner.

"How to artificially improve the measurement accuracy within the accuracy range of the instrument? "There are two methods: First, change the measuring range of the meter. For example, for a meter with a temperature of 0-800 degrees, the maximum measurement error is 4 degrees at level 0.5. If it is changed to 0-600 degrees, the maximum measurement error is 3 degrees. The second is to compress the measuring range by migrating. If the maximum flow rate is 40t/h, but the common flow rate is 32t/h, the measuring range can be changed to 20-40t/h, still calculated as level 0.5. When 0-40t/h, the maximum measurement error is 0.2t. After changing to 20-40t/h, the maximum measurement error is 0.1t. This is just an example, provided that changing the range does not affect production.

★ The concept of error is a matter of probability. Our country (and most of the world * * ) The definition of instrument accuracy is determined based on the value of the error distribution within the range of ±3σ. That is to say, an instrument with 0.5% accuracy means that 99.73% of the errors in infinite measurements will not exceed 0.5% (there is a 99.73% possibility that the error will not exceed 0.5% in one measurement) ； ★ The possibility of a 1% error between two meters with an accuracy of 0.5% exists, but the probability is very low. And theoretically there is a possibility of an error greater than 1%, but the probability is lower. ； ★ When two or more instruments form a system, the accuracy of the system conforms to the following rules (the system accuracy meets the probability mentioned above) where: System accuracy composed of Gn n instruments ； x1, x2…xn Accuracy of the 1st, 2nd…n instruments ； ★ Back to the question itself: When two instruments with a tolerance of ±0.5% are in the same system, the tolerance is (0.5×0.5)^2=0.5(±%).

Under the premise that the instrument accuracy is certain, the method to improve the measurement accuracy is to use multiple instruments to measure at the same time and take their arithmetic average. The arithmetic mean of multiple measurements is the only theoretical way to approximate the true value ； Reducing the instrument range can improve the resolution of readings, but it cannot reduce the measurement error. For example: The measurement tolerance of Class A platinum thermal resistor is ±(0.15+0.002|t|)℃, when measuring 300℃, the tolerance is ±(0.15+0.002×300)=±0.75℃. At this time, even if other secondary meters have no errors and the reading resolution is increased to 0.1°C or higher by reducing the range, etc., it can only reduce the reading error and narrow the margin range in the adjustment system, but it cannot improve the measurement accuracy. Changes in readings less than 0.75°C when measuring a temperature of 300°C are not credible (reduced confidence). In actual operation, measurement accuracy can be improved by using higher-precision sensors. For example: For the same 0-100KPa range transmitter (EJA110A), the measurement accuracy obtained by selecting the membrane box M will be higher than that of the membrane box H. ； In addition, for some types of sensors and their instrument systems, reducing the measuring range does have the effect of improving accuracy. For example: In the above example, membrane box H is also used, and the measurement accuracy of the transmitter with a range of 0-100 is higher than that of 0-500. .

This post was last edited by xxkhc on 2022-4-12 18:29 We know that the accuracy level of an instrument is represented by the maximum reference (full scale) error of the instrument, and the accuracy level of the instrument is divided by the size of the maximum reference error. The reference error, also known as the full-scale error, is the relative error expressed as a percentage of the absolute error and the full-scale value (full range) of the instrument. The reference error of the instrument = the absolute error limit of the instrument / the range of the instrument × 100% ； It can be seen from the above that the measuring range of the instrument will affect the reference error of the instrument. For the same measuring instrument, if the measured value is smaller, the relative error will be larger. In order to improve the measurement accuracy, you can take: First, choose an instrument with an appropriate accuracy level ； The second is to select an instrument with an appropriate range according to the measured value. It is based on the second point above that it is recommended to appropriately reduce the range of the meter if production allows, so that the measured value of the meter is closer to the upper limit of the meter to reduce measurement errors.