What are the methods for handling thermal resistance temperature measurement and anti-interference issues?

Change the signal grounding method

The thermal resistance temperature measurement signal is usually wired using a three wire system, using KYVRP4 × 1.5 shielded cables to lead to the CCF relay cabinet in the PC room of the DCS site station. The cable is shielded and grounded inside the relay cabinet. The solution is to connect the B and b of the thermal resistor Pt100 to the cable shield at the terminal of the relay cabinet, and introduce the interference signal into the ground. This method can eliminate the interference signal and restore the normal temperature display of the computer.

Change the signal transmission method

It is possible to install a Pt100 thermistor temperature converter in the on-site or on-site station PC room to convert the Pt100 resistor signal into a standard DC4-20mA signal and change the computer input signal channel accordingly. This method can also eliminate interference generated during signal transmission and restore the temperature displayed on the computer to normal. Because the DC4-20mA signal has strong anti-interference ability, the installation location of the temperature converter can be determined according to the actual situation on site. However, choosing indoor installation has the disadvantage of increasing equipment investment and requiring the power supply of the converter.

1. Isolation law

The isolation method is to install the thermistor in a suspended manner, so that the thermistor does not come into contact with the refractory bricks on the furnace wall. Insulation is also used to isolate the thermistor from the support. This method can effectively prevent high-temperature leakage interference.

2. Shielding method

The shielding method is to shield the compensating wire of the thermistor by threading it inside an iron pipe or other metal shielding material. This can prevent electromagnetic interference and interference from high-voltage electric fields. When using this method, the iron pipes and shielding materials should be well grounded, and the compensating wires should be twisted together.

3. Grounding method

This method involves grounding the measurement circuit and introducing interference into the ground to ensure the measurement accuracy of the instrument. There are two forms of this method: * * grounding the reference terminal of the thermistor, and the second is grounding the measurement terminal of the thermistor.

When using the reference terminal grounding method, one end of the output terminal of the thermistor (or compensating wire) is grounded through a sufficiently large capacitor (the larger the capacitor, the better if conditions permit). The measurement terminal grounding method is to ground the measuring terminal of the thermal resistance, which means that a metal wire is led out from the measuring terminal of the thermal resistance and grounded. This method has a good preventive effect on high-temperature leakage interference. When selecting metal wire, it should be high temperature resistant and harmless to the thermistor electrode.

We should be prepared to prevent interference when using thermal resistors. Only in this way can we make the measurement of our thermal resistance more accurate, thus making our work more convenient and effective.

Application of anti-interference

Firstly, avoid strong magnetic fields

Secondly, compensate the wires with shielding

Thirdly, power cables and signal lines should be routed separately to maintain a distance

Reasons for interference in the system

To achieve monitoring and control in industrial production processes, various automation instruments, control systems, and actuators are required. The signal transmission between them includes small signals ranging from weak to millivolts and microamperes, as well as large signals of tens of volts, even thousands of volts and hundreds of amperes; There are both low-frequency DC signals and high-frequency pulse signals, and it is often found that the signal transmission between instruments and equipment interferes with each other, causing instability and even misoperation of the system. In addition to the performance reasons of each instrument and equipment, such as anti electromagnetic interference, another very important factor that causes this situation is the potential difference between the signal reference points between the instrument and equipment, which forms a "grounding loop" and causes distortion during signal transmission. Therefore, to ensure the stable and reliable operation of the system, the issue of "grounding loop" must be addressed in the signal processing process of the system.

The method to solve the "grounding loop"

According to theoretical and practical analysis, there are three solutions:

The first solution is to use signal isolation methods in each process loop to disconnect the process loop without affecting the normal transmission of process signals, thus completely solving the grounding loop problem.

The second solution: all on-site equipment is not grounded, so that all process loops have only one grounding point and cannot form a loop. This method may seem simple, but it is often difficult to implement in practical applications because some equipment requires grounding to ensure measurement accuracy or human safety, and some equipment may form new grounding points due to long-term corrosion and wear or climate effects.

The third option is to make the potential of the two grounding points the same, but due to the influence of geological conditions and climate change on the resistance of the grounding points, this option cannot be completely achieved in practice.