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How to deal with thermocouple temperature and anti - interference problems

Release date: 2017-07-20 09:41:47 Visits: 740

With regard to the thermocouple temperature measurement and anti-jamming problem, some industries currently use DCS distributed distributed computer control system, with strong applicability and high reliability, through software programming can achieve the monitoring of process parameters With control. Although the DCS system hardware configuration is powerful, but there is a problem can not be ignored, if the signal from the scene of the measurement signal in the transmission process into the interference signal, DCS system itself will be difficult to suppress, need to take effective measures to the outside solve. This paper describes the Pt100 thermocouple temperature signal abnormalities caused by fault handling methods.
    1, coal mill system thermocouple temperature signal abnormalities caused by fault handling
    I plant coal mill system bag dust collector ash bucket temperature and coal mill bearing temperature have occurred abnormal temperature anomalies, the phenomenon is in the control room CRT temperature showed a random jump, in the field check the temperature measurement device is normal, in the PC station The resistance value measured by the DT-890C digital multimeter is corresponding to the actual temperature. We have taken the replacement thermocouple, check the temperature signal transmission cable shielded ground, replace the PC signal processing channel and other measures, but no effect. In order to find the cause of the failure, we re-lay a cable, still can not solve the problem, after comparative testing, inspection and analysis, the conclusion is that the temperature signal mixed into the interference signal, for which we have taken the following treatment.
    1.1 Change the signal ground
    Thermocouple temperature signal is usually used three-wire connection, the use of KYVRP4 × 1.5 shielded cable to the DCS site PC room CCF relay cabinet, cable shielding, grounding in the relay cabinet. The solution is to thermocouple Pt100 B, b in the relay cabinet terminal with the cable shield together, the interference signal into the earth, in order to eliminate the interference signal, you can make the computer temperature display back to normal. 1.2 Change the signal transmission mode
    The Pt100 resistance signal can be converted to standard DC4 ~ 20mA signal by adding Pt100 thermocouple temperature converter in the field or site PC room, and the computer input signal channel should be changed accordingly. This method can also eliminate the information generated during signal transmission. Interference, so that the computer shows the temperature back to normal, because DC4 ~ 20mA signal anti-interference ability is very strong, the temperature converter installation location can be determined according to the actual situation on the scene, but the best choice for indoor installation, the shortcomings of this method is to increase the equipment Investment, while the need to provide converter power supply.
    2, cement mill main motor oil station temperature anomaly treatment
    I plant cement mill main motor due to overhaul treatment and the replacement of a new motor, bearing with thin oil lubrication, a corresponding increase in a thin oil lubrication station. The station has four temperature measuring points, lubricating tank temperature, heating oil temperature, oil supply temperature and oil return temperature.
    This station is equipped with a thin oil station commissioning, temperature measurement system, heating control and pump work is normal, put into use. Cement mill system ready to drive production, when the system fan and other equipment to drive, the fuel tank temperature, oil temperature, oil temperature are temperature anomalies show abnormal, and heating oil temperature due to low ambient temperature, the heater work to high oil temperature Affected. Fault phenomenon is in the control room CRT display temperature display in the -30 ~ +30 ℃ between the regular beating, the use of DT-890C digital multimeter to measure the thermocouple resistance did not fluctuate, the replacement of the computer signal channel also did not improve. As the installation of the temperature from the temperature components to the junction box between the use of the transmission line is a common wire, no shielding, it is decided from the PC room to the site of the connecting cable directly connected to the temperature sensor terminal, the control room CRT temperature display normal. 2h after the mill when the main motor is turned on, the temperature again back to zero failure, and 0 ~ +30 ℃ between the irregular beating, due to time constraints we decided to take emergency measures in the PC room will connect the cable shield and B, b The terminals are connected together, the above temperature display returns to normal, the cement mill is normally opened.
    The main motor lubricating oil station is responsible for supplying the lubricating oil to the front and rear bearings of the main motor. If the oil temperature measurement abnormality is abnormal, the main motor can not drive, otherwise the main motor bearing is not effectively protected, will cause a major accident, must be removed before the failure to open the main Motor. Due to time constraints, failed to do quantitative analysis of this failure, but it is certain that this is caused by interference signal failure.
    3, raw mill grinding machine vertical axis of the abnormal treatment
    I plant raw material grinding machine vertical shaft for the German Humboldt products, according to the vertical axis of the installation of the design of the upper and lower three bearing temperature detection.
    In the normal operating conditions, RT50MA detection temperature is about 69 ℃, RT50MB detection temperature is about 78 ℃, RT50MC detection temperature is about 94 ℃. According to the equipment protection requirements, set the bearing alarm temperature H1 is 125 ℃, the shutdown protection temperature H2 is 135 ℃, among which the shutdown protection temperature H2 is one of the conditions of the intermittent parking.
    Since May 2000, in the production conditions and equipment running normally, suddenly RT50MA alarm, sometimes H1 alarm, sometimes H2 alarm, but then returned to normal. When the H2 alarm occurs when the temperature indicates more than 135 ℃, causing the separator to jump, then the raw material mill system chain parking. By checking the thermocouple and wiring are not found problems, to take the transmission signal cable shielding and RT50MA B, b connected with the method failed to eliminate this failure.
    Treatment method: to install the temperature converter method, the resistance signal is converted to DC4 ~ 20mA standard signal input DCS system corresponding signal channel, to solve the RT50MA temperature detection abnormal fault. The temperature converter is installed as much as possible in the external environment, where we installed it in the DCS site PC station CCF relay cabinet.
After RT50MB, RT50MC have also occurred in the same failure, check the thermocouple and wiring no problem, we used the same treatment to solve the problem.
    August I plant equipment maintenance after driving, the separator oil temperature RT-51 suddenly H2 alarm, resulting in the separator driving conditions are not satisfied and can not drive, we immediately proceed to check did not find any problems, then the temperature and recovery Normal display, view the temperature trend similar to RT50MA, we immediately take the above method to solve, so that the raw material grinding system smooth driving.
    4, summary
    Electromagnetic compatibility in industrial and mining enterprises is a prominent and important issue, automatic detection is basically involved in the weak signal, in the signal transmission process vulnerable to electromagnetic interference. By the factory conditions, can not be real-time monitoring of these disturbances, to solve the interference caused by the greater difficulty, but in the case of conditions should make the cable to the rationalization of the direction and distribution, that is, the strength of cable laying, if necessary The installation of shielded protection for weak electrical signal cables is an important anti-jamming.

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