At present, the DCS distributed computer control system is widely used in this industry, which has strong applicability and high reliability. Through software programming, the monitoring and control of 

process parameters can be achieved, making the cement production process automated. Due to the powerful hardware configuration of the DCS system, signals such as Pt100 thermal resistance temperature measurement signal, K-type thermocouple temperature measurement mV signal, pulse switch quantity, and standard voltage and current signal from the primary detection instrument on the cement production site can be directly processed. However, there is an issue that cannot be ignored. If the process parameter measurement signal from the site is mixed with interference signals during transmission, the DCS system itself will be difficult to suppress, and effective measures need to be taken externally to solve it. This article introduces the handling methods for faults caused by abnormal temperature measurement signals of Pt100 thermistor.

       Fault handling caused by abnormal temperature measurement signal of thermal resistance in coal mill system

    The temperature display is abnormal, and the phenomenon is that the temperature display on the CRT in the central control room jumps irregularly. On site inspection shows that the temperature measuring element is normal. The resistance value measured using a DT-890C digital multimeter at the relay terminal of the PC station corresponds to the actual temperature. We have taken measures such as replacing the thermal resistor, checking the shielding grounding of the temperature measurement signal transmission cable, and replacing the PC signal processing channel, but none of them have been effective. In order to find the cause of the malfunction, we laid another cable, but still couldn't solve the problem. After comparative testing, inspection and analysis, the conclusion was that interference signals were mixed in the temperature measurement signal. Therefore, we adopted the following processing methods.

1.1 Changing the signal grounding method

    The thermal resistance temperature measurement signal is usually connected in a three wire system, using KYVRP4 × 1.5 shielded cable to be led to the CCF relay cabinet in the DCS field station PC room. The cable is shielded and grounded inside the relay cabinet. The solution is to connect the B and B of the thermal resistance Pt100 with the cable shield at the relay cabinet terminal, introduce interference signals into the ground, and eliminate interference signals in this way, so as to restore the computer temperature display to normal.

1.2 Changing the Signal Transmission Method

    The Pt100 resistance signal can be converted into a standard DC4-20mA signal by installing a Pt100 thermistor temperature converter in the on-site or on-site station PC room, and the computer input signal channel can be changed accordingly. This method can also eliminate interference generated during signal transmission and restore the temperature displayed by the computer to normal. The anti-interference ability of DC4-20mA signals is very strong, and the installation position of the temperature converter can be determined according to the actual situation on site. However, the disadvantage of choosing indoor installation is that it increases equipment investment and requires the provision of converter power.

Handling of abnormal temperature in the thin oil station of the 2 main motors

    The main motor was replaced with a new motor due to major repairs, and the bearings were lubricated with thin oil. A corresponding thin oil lubrication station was added. The oil station is equipped with four temperature measurement points, including lubrication oil tank temperature, heating oil temperature, supply oil temperature, and return oil temperature.

    This thin oil station has been installed and debugged, and the temperature measurement system, heating control, and oil pump are working normally. It has been put into use. The cement mill system is preparing to start production. When the system fan and other equipment are started, there are abnormal temperature display faults in the oil tank temperature, supply oil temperature, and return oil temperature. However, the heating oil temperature is not affected due to the low ambient temperature, and the heater works, causing the oil temperature to be high. The fault phenomenon is that the temperature displayed on the CRT display in the central control room fluctuates irregularly between -30 and+30 ℃. The DT-890C digital multimeter was used on site to measure the above thermal resistance value without fluctuation, and there was no improvement after replacing the computer signal channel. Due to the discovery during installation that the transmission wire between the temperature measuring element and the on-site junction box was a regular wire without shielding, it was decided to directly connect the connecting cable from the PC room to the temperature measuring element terminal. The temperature display on the CRT in the central control room was normal. After 2 hours, when the main motor of the mill was turned on, the above temperature experienced a return to zero fault again, and the temperature fluctuated irregularly between 0 and+30 ℃. Due to time constraints, we decided to take emergency measures in the PC room to connect the connecting cable shield with terminals B and B. The above temperature displays returned to normal, and the cement mill started normally.

    The main motor lubricating oil station is responsible for providing lubricating oil to the front and rear bearings of the main motor. If the temperature measurement of the lubricating oil is abnormal, the main motor cannot be started. Otherwise, the main motor bearings cannot be effectively protected, which can cause major accidents. The fault must be eliminated before the main motor can be started. Due to time constraints, quantitative analysis of this fault was not possible, but it can be confirmed that it is caused by interference signals.

Handling of abnormal vertical axis temperature

    The vertical shaft is a product of Hamburg Company in Germany, and the temperature detection of the upper, middle, and lower bearings is designed according to the installation position of the vertical shaft.

On the control panel CRT in the central control room, the displayed temperatures are RT50MA, RT50MB, and RT50MC Sepa Bear Temp. Under normal operating conditions, the RT50MA detection temperature is around 69 ℃, the RT50MB detection temperature is around 78 ℃, and the RT50MC detection temperature is around 94 ℃. According to the equipment protection requirements, set the bearing alarm temperature H1 to 125 ℃ and the shutdown protection temperature H2 to 135 ℃. Among them, the shutdown protection temperature H2 is one of the conditions for the interlocking shutdown of the powder selection machine.

Since May 2000, under normal production conditions and equipment operation, RT50MA alarms have suddenly occurred, sometimes with H1 alarms and sometimes with H2 alarms, but have since returned to normal. When an H2 alarm occurs, the instantaneous temperature indication exceeds 135 ℃, causing the powder selection machine to trip and immediately causing the raw material grinding system to interlock and stop. By checking the thermal resistance and wiring, no issues were found, and the method of connecting the shielding of the transmission signal cable to B and B of RT50MA failed to eliminate this fault.

Solution: The method of installing a temperature converter was adopted to convert the resistance signal into a DC4-20mA standard signal and input it into the corresponding signal channel of the DCS system, solving the RT50MA temperature detection abnormal fault. The temperature converter should be installed in a place with a good external environment as much as possible. We will install it in the CCF relay cabinet of the DCS on-site PC station.

    In the future, RT50MB and RT50MC also experienced similar faults. After checking the thermal resistance and wiring, we adopted the same treatment method to solve the problem.

In August, when our factory's equipment was being repaired and started, the lubricating oil temperature RT-51 of the powder selection machine suddenly triggered an H2 alarm, causing the conditions for starting the powder selection machine to not be met and unable to start. We immediately began to inspect and did not find any problems. The temperature returned to normal display, and the temperature trend was similar to RT50MA. We immediately adopted the above methods to solve the problem and ensure the smooth operation of the raw material grinding system.

4 Summary

    Electromagnetic compatibility is a prominent and important issue in ship applications, and automatic detection mainly involves weak electrical signals, which are highly susceptible to electromagnetic interference during signal transmission. Due to the limitations of factory conditions, real-time monitoring of these interferences cannot be carried out, which poses great difficulties in solving anti-interference work. However, if conditions permit, cable routing and distribution should be rationalized, that is, strong and weak cables should be laid in layers. If necessary, installing shielding protection for weak signal cables is an important anti-interference measure