The functions and principles of temperature compensation and pressure compensation

To eliminate the effects of temperature changes on circuits, some temperature-sensitive components (or wires) are used to counteract these effects............... ：） In some electronic products, electronic components with positive and negative temperature coefficients are employed; taking resistance as an example, those with a positive temperature coefficient see their resistance value increase as the temperature rises, while those with a negative temperature coefficient behave in the opposite way. In practical applications, such as in the construction of sensors, using only components with one type of temperature coefficient results in relatively large errors. By combining components with positive and negative temperature coefficients, the effects of these temperatures can cancel each other out, resulting in smaller errors. Compensation devices are used to keep values such as current and frequency within a specified range, so that errors caused by changes in the temperature of the components do not occur. I try to think of an example, but I can’t come up with one, so I had to look up more information. In short, changes in temperature or pressure can affect the accuracy of sensors, but the use of compensation components allows these changes to be offsetted, thereby maintaining the sensor’s accuracy

It seems there’s a formula that can be used for calculation, but I wasn’t able to find it either

Simply put, when pressure or temperature changes and the measurement values change as well, pressure or temperature compensation is required, such as when measuring gas flow rates

Generally, when measuring flow rate, changes in temperature and pressure cause the density of the fluid being measured to change as well, which leads to measurement errors in the flow meter. To reduce errors, temperature and pressure compensation can be employed to minimize measurement errors. The so-called temperature and pressure compensation is essentially a density correction measure taken when the temperature and pressure of the medium do not match the values used during design. Some flow meters are integrated, so no additional calculations are required. In other cases, it is necessary to install separate pressure and temperature sensors near the flow measurement point, and then calculations must be carried out manually in the PLC or DCS using temperature and pressure compensation formulas.

It’s purely meant to serve as a starting point for further discussion. For example, a flow meter measures the volumetric flow rate of the fluid. The gas flow rate is generally the volumetric flow rate under standard conditions. At this point, it needs to be converted to the specific discharge under operating conditions. At this point, the operating condition is such that the temperature and pressure of the medium are compensated for by measuring the pressure or temperature corresponding to the flow rate.

6# jinyue: May I ask? When a gas medium flows through a valve, the flow rate is given in Nm3/h, which represents the volume flow rate under standard conditions. However, the operating temperature and pressure are usually not at standard conditions; is it necessary to take temperature and pressure compensation into account?

Back to upstairs: Only pressure compensation is needed. Can anyone tell me the formula for compensating the temperature and pressure of superheated steam?

Thermal and pressure compensation is merely a correction for the measuring instrument, as the operating conditions under which it is used differ from those under which it was calibrated at the factory；

Flow rate, temperature, pressure – all are fed into the DCS, configured, and that’s it

Flow rate can be classified into three forms based on flow formulas or measurement units: Volumetric flow rate: The flow rate expressed as volume per time or capacity per time. For example: m/h, l/h. Volumetric flow rate (Q) = average flow velocity (v) × cross-sectional area of the pipe. Mass flow rate: The flow rate expressed in mass per unit time. For example: kg/h. Mass flow rate (M) = density of the medium (ρ) × volume flow rate (Q) = density of the medium (ρ) × average flow velocity (v) × cross-sectional area of the pipe. Weight flow rate: The flow rate expressed in terms of force per unit time. Such as kgf/h. Weight flow rate (G) = specific gravity of the medium (γ) × volume flow rate (Q) = density of the medium (ρ) × acceleration due to gravity (g) × volume flow rate (Q) = acceleration due to gravity (g) × mass flow rate (M). There are two ways to express the flow rate depending on the state of the medium: Actual flow rate: refers to the flow rate under the existing conditions of the medium ； 　　Standard flow rate: refers to the flow rate of a medium under specified conditions. 　　For example, for a certain gas with the same mass flow rate, its volumetric flow rate is 1 m/h when it is under compressed conditions; whereas at standard conditions (such as 1 atmosphere pressure and 20°C), its volumetric flow rate may be 10 m/h. 　 Flow rate can be expressed in two ways based on the measurement time: Instantaneous flow rate: This refers to the flow rate over a time interval that is infinitely close to 0, expressed as a value per unit of time. 　　Cumulative flow rate: refers to the total amount of flow that passes through a flow meter within a certain period of time. Temperature and pressure compensation for flow rate: As can be seen from the flow formula, in order to determine the mass flow rate or weight flow rate, it is necessary to know the density (ρ) of the medium ； At the same time, it is necessary to convert between the actual flow rate and the standard flow rate, and it is also important to know the density (ρ) of the medium under different conditions. Under different temperature and pressure conditions, the density (ρ) of a substance varies. 　　In terms of practical application, most flowmeters are calibrated using standard flow rates. And most flow meters, except for specialized mass flow meters, operate on the principle of measuring flow velocity. In the expression of flow rate, the medium density (ρ) is artificially specified based on the actual operating conditions of the medium. When the actual operating conditions change and deviate from those designed, the measurement results of the flow meter will be inaccurate. 　　For gases that obey the ideal gas law, as well as media whose density is linearly related to temperature and pressure. As long as the temperature and pressure changes remain within certain limits and the composition of the medium does not change, it is possible to measure the temperature and pressure simultaneously while measuring the flow rate, and then correct the measurement errors of the flow meter resulting from deviations from the operating conditions specified during design by performing calculations. This process is called thermopressure compensation (or temperature compensation, pressure compensation). 　　With the widespread use of computer technology, for certain media, its density (ρ) can be calculated by measuring its temperature and pressure, which is then used to indicate flow rate. Although these types of flowmeters have extremely high measurement accuracy, due to the asynchronous and discontinuous nature of the calculations, they only provide density and flow velocity values averaged over time; therefore, their instantaneous flow rate is not a mass flow rate, and they cannot be considered mass flowmeters. Since its measurement and configuration methods are still generally regarded as temperature-pressure compensation (or temperature compensation, pressure compensation).