What is a Temperature Transmitter?
Let’s dive into the world of temperature transmitters! 🌡️
A temperature transmitter is a crucial electronic device used to accurately convert signals from various temperature sensors, such as thermocouples, RTDs (Resistance Temperature Detectors), or thermistors, into standardized instrumentation signals.
These signals provide valuable information about the temperature of the process being measured and controlled.
Temperature transmitters utilize common output signals like 4-20 mA or 0-10V DC, where specific current or voltage values represent corresponding temperature ranges.
Let’s take an example !!
Where the temperature transmitter uses a 4-20 mA signal – In this case, 4 mA could indicate 0°C, while 20 mA would correspond to 100°C.
The temperature signal, obtained from the temperature sensor, is then transmitted to a controller. The controller evaluates the current temperature and determines the necessary actions to be taken in the process, such as adjusting the temperature up or down.
These actions are carried out by relevant instruments under the guidance of the controller, ensuring optimal temperature control and regulation.
Working principle of a Temperature Transmitter
A temperature transmitter operates by translating the input from a temperature sensor into a proportional current signal, which is derived from a DC power supply.
The current signal represents the actual temperature and is transmitted as a variation in the power supply. For example, a thermocouple input transmitter draws 4 mA at the lowest temperature and proportionally increases the current as the temperature rises until it reaches 20 mA, corresponding to the maximum temperature sensed by the sensor.
This current range, such as 4-20 mA, is used to represent the temperature range, such as 0-100 ℃.
When using an RTD, a Wheatstone bridge is employed to generate a low voltage, which is then amplified to produce a 4-20 mA signal. In some cases, the analog signal may be converted to a digital signal for additional functionalities like calibration and scaling before being converted back to an analog signal. The conditioning circuitry of the transmitter can be designed to accommodate a wide range of resistance values to cater to different RTD types.
As temperature changes, the thermocouple voltage or RTD internal resistance fluctuates, causing the output current to vary between 4 and 20 mA. These variations are processed by internal circuits, converted into temperature data by a converter, and subsequently transmitted to the control room.
Temperature transmitters are available in different types and are categorized as either wireless or wired. The wired transmitters can be further classified into 2-wire and 4-wire configurations, offering different options for system integration and communication.
Why use temperature transmitters?
In situations where remote process temperature monitoring is required, the use of temperature transmitters becomes crucial. These transmitters play a vital role in amplifying and conditioning the small signals generated by temperature sensing devices like thermocouples and RTDs.
By converting the sensor signals into usable levels, temperature transmitters enable the transmission of temperature data through standard copper wire.
This transmitted signal can then be utilized to drive various equipment such as meters, dataloggers, chart recorders, computers, or controllers, allowing for accurate and reliable temperature measurement and control.
2-Wire Temperature Transmitter
Temperature transmitters are typically designed as two-wire devices, combining the functions of power supply and signal transmission within the same pair of wires.
4-Wire Temperature Transmitter
The 4-wire temperature transmitter utilizes two distinct circuits. Two wires are dedicated to connecting to the power supply, while the other two wires are used for establishing a connection with the controller. The power supply for the transmitter can vary between AC or DC, depending on the specific manufacturer and model of the device.
Types of temperature transmitters based on shapes and sizes
Temperature transmitters are available in a diverse range of shapes and sizes, offering flexibility to suit various applications and environments.
Temperature transmitters can be classified into various types based on their shapes and sizes. Here are some common types:
Product Images Credit: Electronet, Vivace, E&H, ABB
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Head-mounted Temperature Transmitter: These transmitters are compact and designed to be installed directly on the temperature sensor head. They are commonly used in industrial processes and offer easy integration with existing sensor assemblies.
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Din Rail Temperature Transmitter: These transmitters are designed to be mounted on a DIN rail, commonly found in control panels or electrical cabinets. They provide a convenient and organized solution for temperature measurement and control in industrial environments.
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Field-mounted Temperature Transmitter: Field-mounted transmitters are designed for installation in the field, away from control rooms or central control systems. They are rugged and resistant to harsh environmental conditions, making them suitable for outdoor or remote temperature monitoring applications.
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Wall-mounted Temperature Transmitter: These transmitters are designed for wall mounting and are commonly used in building automation systems, HVAC (Heating, Ventilation, and Air Conditioning) applications, and indoor temperature monitoring.
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Wireless Temperature Transmitter: Wireless transmitters eliminate the need for wired connections by using wireless communication protocols such as Wi-Fi or Bluetooth. They offer flexibility in installation and are suitable for applications where wired connections are impractical or not feasible.
Inputs of Temperature Transmitter
Temperature transmitters can accept different types of inputs depending on the temperature sensor used. Here are some common types of inputs supported by temperature transmitters:
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Thermocouple (TC): Thermocouples are temperature sensors that generate a voltage signal based on the temperature difference between two different metals. Temperature transmitters with thermocouple inputs can accommodate different types of thermocouples such as Type K, Type J, Type T, etc.
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Resistance Temperature Detector (RTD): RTDs are temperature sensors that change resistance with temperature. Temperature transmitters with RTD inputs can support various RTD types like PT100, PT1000, etc.
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Thermistor: Thermistors are temperature-sensitive resistors that change resistance with temperature. Temperature transmitters with thermistor inputs can work with different types of thermistors such as NTC (Negative Temperature Coefficient) or PTC (Positive Temperature Coefficient).
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Voltage: Some temperature transmitters can directly accept voltage inputs, such as 0-10V DC or 0-5V DC, generated by temperature sensors that provide voltage output signals.
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Current: Certain temperature transmitters can handle current inputs, typically 4-20mA or 0-20mA, which are commonly used in industrial applications for temperature measurement.
It’s important to choose a temperature transmitter that supports the specific input type required by the temperature sensor being used.
This ensures accurate and reliable temperature measurement and compatibility between the transmitter and sensor.
Outputs of Temperature Transmitter
Temperature transmitters provide various types of outputs to interface with different types of control systems, instruments, and devices. Here are some common types of outputs supported by temperature transmitters:
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Analog Current (mA): The most common output type is analog current, typically 4-20mA or 0-20mA. This current signal represents the temperature measurement, with 4mA usually corresponding to the lowest temperature and 20mA corresponding to the highest temperature.
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Analog Voltage (V): Some temperature transmitters offer analog voltage outputs, such as 0-10V DC or 0-5V DC. The voltage signal represents the temperature measurement within the specified range.
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Resistance: Certain temperature transmitters provide a resistance output, typically in the form of a change in resistance based on the measured temperature. This type of output may be suitable for specific applications or systems that require resistance-based signals.
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Digital (Fieldbus): With advancements in digital communication protocols, temperature transmitters now support digital outputs such as various Fieldbus protocols (e.g., Foundation Fieldbus, Profibus, Modbus). These protocols enable seamless integration with digital control systems and devices.
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Wireless: Modern temperature transmitters also offer wireless communication options, allowing temperature data to be transmitted wirelessly to compatible receivers or systems. Wireless protocols like Bluetooth, Wi-Fi, or Zigbee may be utilized for this purpose.
The choice of output type depends on the compatibility with the receiving device, the communication protocol used in the system, and the specific requirements of the application.
Advantages of using temperature transmitters
Using temperature transmitters instead of direct-wired connections offers several advantages, including:
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Improved Noise Immunity: Temperature transmitters are designed to provide better electrical noise rejection, ensuring accurate and reliable temperature measurements. They are built with signal conditioning capabilities that help minimize the impact of external electrical interference, resulting in more stable and accurate temperature readings.
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Extended Distance Capability: Temperature transmitters allow for longer distance transmission of temperature signals without significant signal degradation. This eliminates the need for expensive extension wires, as the transmitter can amplify and transmit the signal over longer distances, reducing installation and maintenance costs.
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Local Indication and Control: Many temperature transmitters come equipped with local indication and control capabilities. They feature built-in displays or indicators that allow users to monitor temperature readings directly at the transmitter location. Additionally, some transmitters offer local control functions, enabling adjustment of temperature setpoints or other parameters directly at the transmitter, simplifying on-site operation and troubleshooting.
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Advanced Diagnostics: Temperature transmitters often incorporate advanced diagnostic features that provide valuable information about the health and performance of the temperature measurement system. These diagnostics can detect sensor faults, wiring issues, and other anomalies, enabling proactive maintenance and troubleshooting to ensure accurate temperature measurements.
Summary
Temperature transmitters play a crucial role in modern industrial processes where accurate temperature measurement and control are essential.
These compact devices offer numerous advantages over direct-wired connections, including improved noise immunity, extended transmission distances, local indication and control capabilities, and advanced diagnostics.
By using temperature transmitters, users can reduce electrical noise and signal degradation, lower the cost of using extension wires, and gain the ability to monitor and control temperature locally.
The advanced diagnostic features of temperature transmitters enable proactive maintenance and troubleshooting, ensuring reliable and efficient temperature measurements.
With their versatility and reliability, temperature transmitters have become indispensable tools in a wide range of industries, contributing to enhanced process control, improved productivity, and overall operational efficiency.
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