The issue with the thermometer’s sleeve
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May I ask what are the requirements for the compatibility between the thermometer sleeve and the thermometer probe? In other words, must the tip of the thermometer probe be in contact with the thermometer’s sleeve? If there is no contact, the presence of air in the sleeve affects the accuracy of the measurement. I appreciate your advice.
It has no impact; it may cause a delay in measurement, but temperature measurement inherently involves a certain degree of lag. Additionally, there is also a gap between the outer shell of the thermometer control rod you mentioned and the sensing element (such as PT100).
The thermometer sleeve cannot be too thick, otherwise the tip of the probe cannot make contact with the sleeve; this not only leads to delays but also affects the accuracy of the measurement values, as it takes time for heat to be transferred from the sleeve wall to the air inside the sleeve.
There is a gap between the sleeve and the sheath; with the improvement in manufacturing precision these days, this gap is becoming increasingly small. Typically, the difference between the inner diameter of the sleeve and the outer diameter of the sheath is around 0.5 mm. There will be a delay, but it does not affect the measurement accuracy.
There is usually a small gap between the tip of the thermometer probe and the thermometer’s casing. A small gap has little impact on accuracy, while a larger gap does have an effect. Temperature measurement inherently involves some delay, and PID control can help to correct this issue, but it is still best if manufacturers ensure that their products are designed to work together seamlessly.
Regarding response time, if the application requires a high level of responsiveness, it is necessary to design and manufacture the sensor itself, taking into account the processing requirements for the surrounding casing as well. It is important to test the response time at various time constants; in such cases, the cost-effectiveness needs to be considered – whether such a high level of performance is really necessary. Systems engineering involves weighing the investment required; what’s appropriate is sufficient. For example, in the air separation industry, I believe raising the requirements for response time can be beneficial for the manufacturing process. In many industries, it really depends on the design choices made.
…………A small amount of heat transfer oil can be added to the sleeve to improve the heat transfer effect :)
In some cases, the thermometer is inserted from the top; it is quite long, and the device comes equipped with a stirrer. Therefore, the thermometer sleeve needs to be made thicker. To avoid delays in measurement, we add some heat transfer oil to the sleeve, which works well.
Generally, some heat transfer oil is used; in cases where the gaps are large, iron sand is also used