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⌚Timestamps:
00:00 - Intro
01:06 - What is a temperature transmitter?
01:49 - 2-Wire/4-Wire Transmitter
02:19 - Most common temperature sensors
03:13 - HART transmitter
03:51 - Calibration
04:29 - Thermocouple/RTD calibration
05:10 - Old/new style calibration
06:43 - Wireless transmitter
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In this video, we're going to introduce you to a very common device used in process control today, the Temperature Transmitter.
We’ll discuss the sensors used with them, and show you how they are connected in a typical control loop. We’ll also give you an insight into how they are calibrated.
Temperature Transmitters are available in all different shapes and sizes depending on the application and environment they are expected to operate. To name a few, there are:
- DIN rail mounted,
- Field mounted,
- Hockey puck style.
A Temperature Transmitter is a device that converts the signal produced by a temperature sensor into a standard instrumentation signal representing a process variable temperature being measured and controlled.
The most common transmitter instrumentation output signal is 4 to 20 mA.
The signal from the Temperature Transmitter is sent to a Controller that determines what action is required and generates an appropriate output signal.
Controllers are either a PLC or a DCS in process control today.
The Heating/Cooling source exerts a direct influence on the process as directed by the controller.
Most Temperature Transmitters are 2-wire types having only two wires. These two wires provide power for the transmitter and are also the signal lines!
A 4-wire transmitter has two wires connected to a power supply and two signal wires connected to the PLC. The power supply can be AC or DC depending on the vendor and model.
The two most common temperature sensors used in process control are the thermocouple and the Resistance Temperature Detector (RTD).
The thermocouple produces a change in voltage with a temperature change. Thermocouples have only two wires.
An RTD produces a change in resistance with a temperature change. Unlike a thermocouple that has only two leads, an RTD can have two, three, or four leads.
It’s common to see Temperature Transmitters that are capable of working with either an RTD or a thermocouple.
The SMART transmitter is an intelligent transmitter that has an analog output of 4 to 20 mA and also provides digital communication signal information such as Instrument Tag Names, Calibration Data, and Sensor Diagnostics.
These SMART transmitters use HART protocol or FOUNDATION FIELDBUS or PROFIBUS.
A Temperature Transmitter needs to be adjusted or calibrated so that the current output of 4 to 20 mA represents the temperature range of the process variable being measured.
In every calibration scenario, the sensor is replaced by a device that can simulate the output of the sensor over the entire process variable temperature range.
- For a thermocouple, the sensor is replaced by a device that produces a range of millivolts.
- For an RTD, the sensor is replaced by a device that produces a range of resistances. Historically the device that produced a range of resistances was a decade box.
Signal Reference Calibrators can output a variety of electrical signals that can simulate RTDs and Thermocouples making it much easier to calibrate Temperature Transmitters.
Older style Temperature Transmitters have multi-turn potentiometer adjustments called Zero and Span. The Zero pot is adjusted to produce 4 mA when the simulated temperature is 0%, and the Span pot is adjusted to produce 20 mA when the simulated temperature is 100%.
Newer style Temperature Transmitters are programmed or calibrated using the software. The Transmitter is connected to a computer via a serial USB connection.
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#RealPars #TemperatureTransmitter #Instrumentation
3 июл 2024
