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Pressure Transducer Sensitivity/Resolution/Error

During the selection and use of the pressure transducer, three specifications of sensitivity, resolution, and error are often mentioned. However, many people are not very clear about the actual meaning and difference of these three specifications, resulting in large or small problems when using pressure transducers. This paper will explain the meaning and difference of the sensitivity, accuracy and error of the pressure transducer.
  • Pressure transducer Sensitivity
The sensitivity of the pressure transducer refers to under steady-state operation, the ratio of the change Δy in the output amount of the transducer to the change Δx in the input amount. That is, the dimension ratio of the output to the input. For example, for a pressure transducer, the output voltage changes to 200mV when the pressure changes by 1Pa.
The sensitivity of the pressure transducer is the slope of the characteristic curve of the output and input. If there is a linear relationship between the output and the input of the pressure transducer, the sensitivity S is a constant. Otherwise, it will change as the amount of input changes.
When the dimension of the output and input amount of the pressure transducer are the same, the sensitivity can be understood as a gain.
  • Pressure transducer resolution
The resolution of a pressure transducer is the ability of the transducer to feel the smallest change of the measured pressure. The minimum amount of change is that the input changes slowly from a non-zero value. When the change value of the input quantity does not exceed a certain value, the output of the pressure transducer does not change. In other words, the change in the input of the pressure transducer will not be resolved. The output changes only when the input changes more than the resolution.
Resolution is usually understood as the A/D conversion accuracy or the smallest change that can be perceived. Accuracy usually refers to the percentage which is calculated by indication dividing the error, based on a combination of A/D, sensing circuitry, or other factors.
The resolution of a digital pressure transducer is usually determined by the number of bits in the A/D converter. Accuracy is the maximum percentage error when the pressure transducer repeatedly measure the same standard value. It is an specification to measure the accuracy for the pressure transducer after calibration.The value of the resolution is several times higher than the accuracy.
Usually, the pressure transducer has different resolutions at various points in the full-scale range. Therefore, the maximum input change value that can cause a step change in the output in the full-scale range is often used as a specification for measuring the resolution. If the above specifications are expressed as a percentage of full scale, they are called resolution. The resolution has a negative correlation with the stability of the pressure transducer.
  • Pressure transducer error
The measured value displayed on the pressure transducer is called the indication value, which is a reflection of the measured true value. Strictly speaking, the measured true value is only a theoretical value. Regardless of which meter is used, the measured values have errors. In practical applications, the actual true value is often replaced by a contractual true value measured by a meter with appropriate accuracy or determined by a specific method.
The difference between the indication value and the accepted agreement true value is called the absolute error. Expressed by the formula: absolute error = indication value - agreed true value. Absolute errors can often be called for short as errors. When the error is positive, it means that the indication value of the meter is too large. On the contrary, the indication value is too small.
The ratio of the absolute error to the agreed true value is called the relative error, and the commonly expressed as percentage. That is, relative error = absolute error ÷ agreed true value.
Although it is reasonable to measure the accuracy of the pressure transducer by the absolute error as a percentage of the agreed true value, the transducer is mostly used to measure the amount close to the upper limit. Therefore, the range can replace the agreed true value in the formula, and the reference error can be obtained: Reference error (%) = absolute error ÷ range. Taking into account the ratio of the maximum absolute error to the range over the entire range, the maximum reference error of the meter is obtained: Maximum reference error (%) = maximum absolute error ÷ range. The maximum reference error is independent of the specific indication of the meter, so it can better reflect the accuracy of the meter measurement. Basically, the maximum reference error is the main form of the error and one of the main quality specifications of the pressure transducer.
The pressure transducer shall specify the allowable value of the reference error at the time of shipment, which is called for short as the allowable error. If the allowable error of the transducer is denoted by Q and the maximum reference error is denoted by Qmax, the following relationship is satisfied between the two: Qmax ≤ Q.
Any measurement is related to environmental conditions. These environmental conditions include ambient temperature, relative humidity, supply voltage, and installation, etc. The pressure transducer should be operated strictly according to the specified environmental conditions, that is, the reference working conditions. The error obtained at this time is called the basic error. Therefore, if the measurement is performed under non-reference operating conditions, the error obtained at this time contains additional errors in addition to the basic error, which is also called additional error. That is, error = basic error + additional error
The above discussion is basically aimed at the static error of the pressure transducer. Static error refers to the error of the instrument when it is at rest, or the error that is presented when the measured change is very slow. The inertia factor of the meter is not considered at this time. Pressure transducer also has dynamic error. Dynamic error refers to the additional error caused by the inertia delay of the instrument, or the error during the change. Static errors in pressure transducers are more common in applications

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