In this article, you will learn the transmitter used in the process industry. There is not any limitation on the use of the transmitter in the processes but, you have to choose based on your application.
A word transmitter always lures you when you are an instrumentation engineer. As an instrument engineer, you always know what the transmitter is and what it can do.
Let's understand what a definition of the transmitter says,
The transmitter is a device which senses a process variable, convert it into a standard signal (4-20 mA) and transmit that signal to a controller. Simply the transmitter converts the signal into 4 to 20 mA current signal.
It is used to create a standard signal (4-20 mA) proportional to a process variable (level, pressure, temperature, flow, etc.) and transmit that signal to the controller to control the manipulated variable known as final control element or control valve.
Another thing transmitter does is that it maintain that 4 to 20 mA output proportional to the signal which is coming from the sensor. For example, applied pressure to the transmitter irrespective of applied power (24 VDC) till it goes down well below require power (approx. 12 VDC but, in the longer cable run it should be 18VDC due to voltage drop) to turn on the transmitter.
The main functions of the transmitter are:
- Measure a process variable.
- To convert the process variable into a pneumatic or electronic signal. (3-15 psi or 4-20 mA)
- Transmitting these signal to a monitor or a controller.
- To maintain 4-20 mA current signal irrespective of lack of power (18-24 VDC)
The output range of the transmitter is standardized to bring uniformity in the construction of secondary instruments as well as to facilitate them for test and calibration purpose.
(Source : Endress + hauser)
CLASSIFICATION OF THE TRANSMITTER :
Click on the below link to know more about pneumatic and electronics transmitter.
1. Pneumatic transmitter (3 to 15 psi output)
2. Electronic transmitter (SMART transmitter - 4 to 20 mA output)
3. Hybrid transmitter (Analog + SMART)
Analog transmitter does not contain an inbuilt microprocessor. Due to this, you can not connect HART to such ANALOG transmitter.
For the calibration, you have to calculate a range based on your application and have to adjust multiple time to have a result. so basically, you have to calibrate zero and span and for the other points (8 mA, 12 mA, 16 mA), you have to calculate it.
The SMART transmitter as per name is a smart device comes with an inbuilt microprocessor provide ease of integration with HART allows the easy calibration.
With this, you can check a loop by simply connecting with the HART. Diagnostic become so easy and troubleshooting, too.
- Apart from the ANALOG and SMART transmitter you may have seen a hybrid transmitter which is a combination of the both ANALOG and SMART transmitter.
The above-mentioned concept of the transmitter constitutes the basic in all the measurement techniques.
In the upcoming article, I will explain each type of transmitter in the detail and also cover its calibration procedure.
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