Under normal environmental conditions, the filling fluid (such as silicone oil) inside the double-flange capillary tube has good temperature adaptability and can cope with daily temperature changes normally. At this time, no additional thermal insulation measures are necessary, which not only saves costs but also reduces unnecessary maintenance work.
When the ambient temperature is lower than the freezing point of the filling fluid (e.g., in alpine regions or low-temperature environments), the filling fluid may thicken or even solidify, affecting measurement accuracy. In such cases, thermal insulation is required. For example, silicone oil is a commonly used filling fluid. Its viscosity increases at low temperatures. If the ambient temperature is lower than the freezing point of silicone oil, the flow of silicone oil inside the capillary tube will slow down or even stop, leading to inaccurate pressure transmission and thus affecting the measurement accuracy of the double-flange transmitter.
Even if the ambient temperature does not drop below the freezing point of the filling fluid, large temperature fluctuations will change the density of the filling fluid, which in turn causes static pressure changes, resulting in zero drift and measurement errors. For instance, double-flange transmitters installed outdoors experience significant day-night temperature differences. The thermal expansion and contraction of the filling fluid at noon and night will cause changes in the force on the diaphragm capsule, increasing measurement errors. In such cases, appropriate thermal insulation measures are recommended.
If the capillary tube is installed outdoors or near heat sources or cooling sources, the temperature changes will be more complex and intense. To avoid the impact of temperature fluctuations on measurement results, thermal insulation measures should also be considered.
If the capillary tube is installed outdoors, near heat sources or cooling sources, or used under extreme temperature conditions, thermal insulation measures need to be considered to avoid the impact of temperature fluctuations on measurement results.
Although thermal insulation of the capillary tube is required in some cases, it is important to note that the heat tracing should not be too strong, so as not to cause vaporization of the filling fluid and subsequent damage to the instrument.
Whether double-flange capillary tubes require thermal insulation mainly depends on the ambient temperature, the temperature resistance of the filling fluid, and the installation location. Generally, thermal insulation is not needed, but in low-temperature or alpine environments, appropriate thermal insulation measures are recommended to ensure measurement accuracy and normal operation of the equipment.
It is one of the common insulation methods. For example, electric heat tracing tapes are used, which are evenly arranged along the capillary tube and wrapped with insulation materials. This allows the heat generated by the heat tracing tapes to be uniformly transferred to the filling fluid inside the capillary tube, maintaining its temperature within an appropriate range. However, it is important to avoid excessive heat tracing to prevent vaporization of the filling fluid and damage to the instrument.
Installing the measuring head of the double-flange transmitter in a supporting instrument insulation protection box can effectively protect components such as the circuit board and LCD screen of the measuring head, ensuring they meet the operating temperature requirements. At the same time, it can also provide a certain degree of thermal insulation for the capillary tube, reducing the impact of ambient temperature changes on the filling fluid inside the capillary tube.
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