Symbol Standarisation P&ID For Industri Standard piping and instrument symbols are detailed diagrammatic documentation that provides a set of forms & standards for documenting P&IDs and PFDs, including standard shapes for instruments, valves, pumps, heat exchangers, mixers, crushers, vessels, compressors, filters, motors and other connection forms. Here are some symbols on P&ID : So, those are some of the symbols that we will often see when reading piping & instrument diagrams. May be useful.
Temperatur Transmitter
As instrument engineers, we are already familiar with this one device, yes, the temperature transmitter. What is a temperature transmitter?
A temperature transmitter is a device used to monitor temperature, usually in a stream or enclosed space. The way it works is by sending a temperature measurement signal from the sensor to be sent to the temperature control or temperature indicator. The signal from the sensor is converted by the controller at the transmitter into a 4020 mA signal. This signal will be sent to the I/O or PLC for further processing.
There are 2 types of temperature sensors, including:
1. RTD
RTD or resistence temperatur detector works based on the resistance of the material that changes with temperature. An example of a device is the PT100. PT100 is an RTD made of platinum with a reference of 100 ohns = 0 degrees Celsius.
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2. TC
TC or thermocouple works based on 2 pieces of conductor wire of different materials whose ends are joined together. The first wire as a reference and the second wire as a temperature sensor. This difference causes a voltage difference depending on the magnitude of the temperature.
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The temperature sensor of this transmitter equipment is very prone to impact and high pressure, so it is necessary to install a protective device called a thermowell. This thermowell will be attached to the system or process (usually a pipe or tank) and will be in direct contact with the medium whose temperature will be detected.
Thermowell
This thermowell itself has several types based on the type of connection to the process, including: :
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1. Threaded
This type of thermowell uses threads to connect itself to the process. The use of this type is usually for processes with low pressure, but this type is very easy to install and maintain.
2. Flange
This type of thermowell uses a flange as a connector, this flange will then be connected to the flange that is in the process. Almost the same as the threaded type, this type is also easy to install and maintain, but this type is able to work with higher pressure.
3. Welded
This type of thermowell uses the welding method to connect itself to the process, usually the welding used is TIG welding. The advantage of this type is that it is able to withstand very high pressure from the process, but it is a little more difficult in the installation and maintenance process.
Even though they have different connection types for the process, for the thermowell connection with the temperature sensor, it uses the same type of connection, namely the thread type.
In addition to being divided based on the type of connection to the process, thermowells are also distinguished based on their contact with the flow that is in the process, including:
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1. Straight
This type has a cross section that is flat or the same size from one end to the other. However, this type has a few drawbacks, namely it is slow in responding to process temperatures.
2. Tappered
This type has a different cross-sectional area, the lower the cross-sectional area is getting smaller with the same linear ratio. This type has a good ability to respond to temperature readings in the process.
3. Stepped
Almost the same as the tapered type, the stepped type also has a different cross-sectional area from one end to the other, but the difference is that the different surfaces are step or uneven. This type has a very fast response in reading the temperature in the process.
After we have discussed the types of temperature sensors and also the types of connections to the process, now we will discuss the types of cable or wiring connections.
Below is a wiring table for the temperature transmitter.
Transmitter Temperature Wiring Type
1. 2 Communication Cable
This wiring only uses 2 cables, namely 1 positive cable to provide 24 VDC voltage or input power to the transmitter and 1 more cable for negative cable (command) or 4-20 mA signal sending cable. The way it works is that the PLC sends a voltage of 24 VDC to the transmitter and the transmitter returns a 4-20 mA signal to the PLC through the other channel.
This type has advantages such as low power consumption, easy to install, easy to maintain and cheaper. However, it has a disadvantage, namely the low signal reading accuracy.
2. 3 Communication Cable
This type uses 3 wires for connection, each for the positive wire for input power transmitter, negative and command for transmitter output to the PLC. Add this command cable to send a 4-20 mA signal back to the transmitter.
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The advantage is, of course, that the signal accuracy is better, but it costs more or is more expensive.
3. 4 Communication Cable
This type has 4 cables for connection, so the cable for the input power transmitter can use AC supply not only DC as by using 2 or 3 cables.
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The way it works is almost the same as a 3 cable connection, each of these cables is 2 cables for input power to the tramitter, 2 more cables for output to the PLC.
Thus a brief discussion of the temperature transmitter, may be useful.
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