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In winter, when the measured medium is transmitted to the transmitter through the measurement pipeline, the phenomenon of freezing, solidification and precipitation of crystallization often occurs when the ambient temperature is too low, and the normal working temperature range of the instrument used is exceeded due to the low ambient temperature, which directly affects the accuracy of measurement and display of the instrument. For this reason, it is necessary to perform antifreeze treatment on the instrument and the measuring pipeline of the instrument. The objects that need heat tracing and insulation mainly include the transmitter installed in the instrument incubator, the external float type liquid level transmitter or other forms of liquid level transducer installed in the open air as well as testing pipeline and measuring pipeline of pressure, differential pressure, flow and other instruments. Avoid such accidents through model selection or other methods.
1. Selection measures
Select temperature sensor with heat preservation device. According to the type and use of the instrument and the geographical location to be installed, put forward the thermal insulation and antifreeze requirements of the instrument, and then submit it to the manufacturer for processing.
2. Insulation measures
Use thermal insulation materials to keep warm, that is, use thermal insulation materials to wrap the parts of the temperature sensor that are easy to freeze or are afraid of freezing. When winter comes, it is necessary to check and discharge sewage frequently to prevent damage to the thermal insulation materials of the packaging.
3. Heat tracing measures
(1) Steam tracing measures
That is, the use of steam in pipe for heating to keep warm. Check whether the steam insulation pipeline is unblocked or blocked before supplying steam for insulation in winter. It is best to supply steam that is not too hot 24 hours a day, and sometimes it is necessary to adjust the amount of heat preservation steam according to the change of weather temperature, so as to prevent the temperature from being too high to cause the condensate in the pressure pipe of the transmitter to vaporize and affect the work of the transmitter or prevent the temperature from being too low to cause the condensate in the pressure pipe of the transmitter to freeze and affect the smooth operation of the transmitter.
(2) Measures for thermal insulation protection box
a. The electric heat pipe heating insulation box is composed of three parts: the box body, the heater, and the instrument bracket. Its structure is the same as that of the protection box. The difference is that the electric heating device is installed in the box. The electric heating device is composed of electric heat pipe and temperature controller, and the side of the box is equipped with a socket. When the power is turned on, when the box is heated to the required temperature, the temperature controller is connected to the power to continue to heat up. Through repeated work, the temperature in the box can be maintained within a certain range.
b. Steam pipe heat tracing insulation box. The heat tracing pipe is made of metal pipe in the S-shaped structure. The upper and lower parts of the box are welded with welded thru-plate joints and heat tracing pipes. Heat tracing pipe is installed in the box of up-out and down-in, through the circulation of steam in the pipe cavity to achieve the purpose of heating.
c. Add another layer of thermal insulation cotton to the key instrument box, and add glue to seal the door of the incubator and the inlet and outlet pipelines, which can achieve a better thermal insulation and antifreeze effect of the instrument system.
(3) Measures with electric heating tape
Electric heat tracing insulation technology is a heating technology that directly converts electrical energy into heat energy. Install insulation cable, wrap the heating tape on the instrument, or stick it inside the instrument cabinet (but pay attention to the length of the heating tape used, and it should be economical).
(1) Installation measures: reasonably choose the installation location: a place that is dry and free of rain and snow.
(2) Spot inspection measures: when conditions permit, a special person shall conduct technical confirmation and technical treatment on whether the insulation material is damaged and whether the steam pipe is blocked every day.
(3) Alarm measures: if conditions permit, a small sound and light alarm device for steam leakage or power failure can be installed to facilitate the discovery and timely rectification of hidden dangers and adoption of thermal insulation and antifreeze measures.
(4) Inspection measures shall be regularly conducted by the person in charge of regional instrument maintenance according to the scheduled inspection route. During the inspection, it is necessary to check whether the valve of the insulation pipe is normal, whether the insulation box is normal, whether the drainage device is normal, whether the packaging of the insulation material is in good condition, and whether the electric heat tracing power supply components are normal, etc. They should carry out key inspections on the instruments of the easy-to-freeze devices and make inspection records, carry out dry, complete and clean maintenance of the instruments and their thermal insulation and antifreeze measures, and solve the thermal insulation and heat tracing problems that occur on site in a timely manner.