Regarding the transmission distance of temperature measurement points

Let’s use an integrated temperature sensor, that is, a thermistor combined with a temperature transmitter; after all, transmitting 4-20mA is a more reliable method. If control isn’t required, there’s also the option of using Wi-Fi for wireless monitoring of the numerical values: lol. We could use a tablet with GPRS capabilities, or even a 485 interface, but that would require more development work.

Using a temperature sensor is the best option; with thermal resistors, a range of up to 1000 meters is no problem at all with a three-wire connection

Direct integrated temperature control – solves all problems

In terms of cost and ease of installation, it is best to use a three-core cable directly to the control room. Temperature variation requires investment and calibration; cables are also needed. The lifespan of integrated thermal resistors is not long, and they lack the versatility of conventional types. The factory used a batch of such resistors in the past, but they were all phased out eventually. The three-wire system is used to eliminate the effect of resistance in the transmission cables on measurements, thus there is no need to consider the resistance errors introduced by cable transmission. However, for accuracy, the same three-core cable must be used; two two-core cables cannot be used as a substitute for a three-core one. The shielding layer of the cable must be reliably grounded at the secondary meter.

On-site installation is not the same as in the laboratory. The on-site personnel carried out the installation in a rough and brutal manner. When assisting them with driving while the instruments in the new area were being outsourced, I noticed that many instrument technicians were using 300-pound wrenches to forcefully twist the universal joints, which ended up causing the rubber hoses connected to those joints to become damaged. The same is true for this integrated temperature sensor; rough handling during disassembly and installation can cause damage to the thermal resistance as well as the delicate wiring of the transmitter, making it more difficult to strip the wires and reconnect them. Furthermore, the sealing of the junction box covers on site is also an issue. A simple thermal resistance seal isn’t effective enough to prevent water from entering; in such cases, it’s sufficient to wipe the area clean. However, with integrated units, if they get flooded, they are completely ruined – the components inside rust and it becomes impossible to see their original appearance. Although our factory has its own calibration room, ordinary thermal resistance thermocouples are rarely sent there for calibration. As for the integrated types, it’s not possible to calibrate them on-site because it involves adjusting the zero and full-scale outputs; it’s difficult to set the zero point there. It’s possible to remove them and take them to the calibration room for calibration, and they will indeed carry out the calibration, but behind the scenes people will criticize such actions – after all, those calibration rooms are accessible only through various connections of the management, and they essentially function as idle offices meant to support the managers’ wives. Everyone does this out of a sense of duty, but no one wants to be criticized. So when performing repairs on-site, people just roughly adjust the zero and full-scale settings, and one can imagine how inaccurate the results are. As a result, the process engineers keep asking for better accuracy, which leads to people getting frustrated and, in an emotional fit, converting those integrated devices into ordinary ones – some even simply break them using pliers. Hehe. . .

Another reason why the site is reluctant to install integration or temperature control systems is that it makes fault troubleshooting more complicated. Those who work in technology focus on the accuracy, performance, stability of instruments, as well as their overall precision. Most people who work with field instruments do so simply to make a living; their salary is fixed and not related to the amount of work they do. As a result, their general attitude is to do as little work as possible. For on-site temperature measurement, a thermistor is used, and the data is transmitted to the control room via a three-wire connection. When process engineers say that the temperature reading is inaccurate, most instrument technicians will first go to the thermistor cable in the control room to measure its resistance value, and then roughly calculate whether the actual temperature matches the one displayed, as well as to check for any signs of short circuits or open circuits. Only if it is determined that the resistance value of the cable falls outside the normal range is it necessary to go to the site for inspection. After all, the conditions at the site are not as good as those in the control room; there are issues related to the operating environment there – tight spaces, trenches, as well as various toxic fumes, gases, and substances that adhere to equipment and pipelines. Most people do not want to go to such sites. Even those who do go back, their work uniforms are usually covered in dust. Therefore, most people are reluctant to work with instruments at the site. If an integrated temperature sensor is installed on-site, or a separate temperature sensor is used, it’s not possible to determine the temperature simply by measuring the current in the control room. This is because there is also a transmitter on-site, and there is a possibility that the transmitter could fail. Therefore, if such a temperature sensor is present, the technician must go to the site to check it; there is basically no other option. To troubleshoot the issue on-site, one first needs to check the thermal resistance at the connections of the temperature sensor, and then examine its output. Additionally, issues related to the sensor’s zero point and linearity come into play, so it’s difficult to ensure that the temperature instrument is functioning properly just by measuring the current. The process engineers won’t be confident about the instrument’s performance in such cases. And if the process engineers insist on getting accurate readings, and the zero point of the temperature sensor shifts again, it will only lead to further problems. It’s also difficult to determine the zero point on-site, as the zero point of a temperature sensor corresponds to zero degrees, and it’s hard to find such a constant zero-degree reference point for checking it. Without a base point, only disassembly for calibration is possible, which turns what was originally a simple task into a complicated one. That’s why everyone resists on-site temperature change installation. This mindset is that of advanced domestic instrument repair workers, because their wages, just like those of road workers, are based on daily work done rather than performance; since the wage amount is fixed, their goal becomes to do as little work as possible.