Views:3 Author:Site Editor Publish Time: 2021-11-22 Origin:Site
In the past, the traditional temperature measurement method was to use the direct connection method of the sensor, and the thermal resistance or thermocouple output an ohm or millivolt signal to the DCS or secondary meter. Generally, the on-site temperature measurement point is far away from the control room, and a long compensation wire is required. At the same time, the DCS must be equipped with a special temperature I/O card. The measurement accuracy and performance of this traditional measurement method are poor. The longer the compensation wire between the temperature point and the DCS, the worse the overall performance of the temperature measurement; the thermocouple compensation wire is more expensive than the ordinary 4-20mA copper wire Many, the cost of the compensation wire is a non-negligible part of the total cost of temperature measurement; the millivolt signal of the thermocouple is susceptible to interference. According to statistics, the common industrial noise level is 10mV, which will cause a K-type thermocouple to a peak of about 28℃ Signals can sometimes even cause the process to stop.
Now, by using temperature transmitters, the accuracy/overall performance of temperature measurement can be improved, the installation is convenient, the flexibility is large, and the overall cost of installation, maintenance and operation can be reduced. Rosemount can provide a variety of temperature transmitters to meet the different temperature measurement requirements of various critical measurement points and non-critical measurement points.
I. Improve the accuracy/overall performance of temperature measurement
a. The transmitter fine-tunes its internal temperature curve according to the actual curve of the sensor, which can greatly reduce the interchangeability error of the sensor (up to 75%); 644H and 644R intelligent temperature transmitter-transmitter and sensor comparison function , Matching function 3144 and 3244MV intelligent temperature transmitter-transmitter and sensor matching function;
b. During thermocouple measurement, the transmitter converts the millivolt signal into a 4-20mA signal that is less sensitive to noise, which improves the anti-interference ability and greatly shortens the length of the compensation wire;
c. Eliminate the cold junction compensation error of the thermocouple. 244EH and 244ER PC programmable temperature transmitter, 644H and 644R smart temperature transmitter, and 3144 and 3244MV smart temperature transmitter, all have automatic cold junction compensation function;
d. The 3244MV intelligent temperature transmitter has the function of temperature difference measurement. The accuracy of temperature difference measurement is better than that of using two transmitters to measure separately and then send to DCS (or send the signals of two sensors directly to DCS) and then calculate the temperature difference. The accuracy is several times higher.
II. Easy to install
a. After using the transmitter, all cables are the same and are ordinary copper wires;
b. It is easier to stretch a copper cable than to stretch the compensating wire of a thermocouple;
c. The wiring of the cable is easier, and there is no special rule to avoid the power supply.
III. Great flexibility
a. When using a temperature transmitter, the temperature measurement is 4-20mA signal like other process measurements (such as pressure, liquid level, flow), and DCS can use the same I/O card;
b. The temperature input can be combined with the input of other transmitters, without the need to configure a special I/O card for thermocouples and thermal resistances.
IV. Reduce the overall cost of installation, maintenance and operation
a. Copper cables are cheaper than compensating wires of thermocouples;
b. The use of copper cables eliminates the need for separate cable racks and conduits, which means lower installation costs;
c. The I/O card types of DCS are the same, reducing the number of cards and the number of unused terminals;
d. The intelligent transmitter has a diagnostic function, which can detect and judge whether it is a sensor failure or a process alarm, thereby reducing the number of on-site maintenance, which means a lot of maintenance savings;
e. Better temperature measurement performance can increase productivity, which means great production savings.
Rosemount not only has a full range of high-precision, high-reliability, and high-stability temperature transmitters and temperature sensors, but also various temperature measurement application experience and solutions, which can provide users with a suitable solution for temperature measurement plan.
Rosemount 248 complete temperature assembly includes a smart top-mounted temperature transmitter, the transmitter is equipped with a single model top junction box, sensor, thermowell and extension.