Temperature Sensors vs Temperature Transmitters

Working with temperature sensors and temperature transmitters can be complex, but with the right knowledge, they become highly effective tools for precise temperature measurement. To use them efficiently, it's essential to understand not only their differences but also how they work together to monitor and transmit temperature changes accurately.  

Below, we'll break down the distinction between temperature sensors and temperature transmitters, as well as how they interact to ensure reliable temperature measurement in various applications.

Temperature Sensor  

A temperature sensor is a device that measures temperature and converts it into an electrical signal. It typically consists of two metals that generate electrical voltage or resistance when they detect a change in temperature. This electrical response enables precise temperature measurement and monitoring. To learn more about how a temperature sensor functions, click here.

Temperature sensors are crucial in maintaining specific temperatures within various equipment, from pharmaceutical production to brewing beer. In these industries, the accuracy and responsiveness of temperature control systems are essential to ensuring the final product meets the desired standards.

Temperature sensors come in various types, each designed for different methods of temperature management. The most common types include...

Types of Temperature Sensors  

Resistance Temperature Detector (RTD)  

An RTD (Resistance Temperature Detector) measures temperature based on the resistance of the RTD element, which changes with temperature. The sensor is typically made from materials like platinum, nickel, or copper, with platinum being the most accurate, though it tends to be more expensive.

Thermocouple  

A thermocouple consists of two wires made from different metals, joined at two points. The voltage generated between these two wires corresponds to the temperature difference. While thermocouples may not offer the same accuracy as RTDs, they boast a wider temperature range (from -200 °C to 1750 °C) and are generally more cost-effective.

Negative Temperature Coefficient (NTC) Thermistor  

An NTC thermistor exhibits a significant, predictable change in resistance in response to temperature variations. This allows for fast and accurate temperature readings. However, due to the non-linear nature of this change, linearization is often required, which involves some mathematical processing.

In simple terms, a temperature sensor detects the temperature of solids, liquids, or gases, providing accurate readings for various applications.

Temperature Transmitters

The temperature transmitter is the device, which connects to the temperature sensor to transmit a signal for monitoring and controlling purposes.

The temperature sensor is generally an RTD, Thermistor or Thermocouple sensor (as mentioned above), which will interface with a DCS, PLC, data logger or hardware display.

A temperature transmitter is an essential device used to isolate, filter out EMC noise, amplify, and convert a temperature sensor's signal into a 4-20mA or 0-10V DC output.  

How a Temperature Transmitter Works  

The 4-20mA transmitters are the most commonly used in manufacturing since most industrial equipment is designed to communicate within this range. Inside the device, the temperature can be scaled to match specific application requirements.  

- 4mA represents -17.7°C (0°F)  

- 20mA represents 37.7°C (100°F)  

The transmitter operates by drawing current from a remote DC power supply, connected to the sensor input. The actual temperature signal is transmitted as a change in power supply, requiring only two copper wires for connection.  

In simple terms, a temperature transmitter acts as an intermediary between the temperature sensor and the control device, ensuring accurate, noise-free, and amplified signal transmission.  

Advantages of Using a Temperature Transmitter  

✔ No need for AC power in remote locations when using a two-wire transmitter  

✔ Resistant to electrical noise, ensuring reliable signal transmission  

✔ Cost-effective, as the required wiring is inexpensive and easy to install

Differences Between a Temperature Sensor and a Temperature Transmitter  

While both a temperature sensor and a temperature transmitter play crucial roles in temperature measurement, their functions are distinct yet complementary.  

- A temperature sensor is responsible for detecting physical temperature changes and converting them into an electrical signal, typically in the form of voltage or resistance.  

- A temperature transmitter is connected to the sensor and serves as an intermediary, converting the sensor's raw signal into a standardized output (such as 4-20mA or 0-10V DC) for monitoring, logging, and control.  

Though they are separate components, they work together to ensure accurate, reliable, and consistent temperature measurement, which is essential for maintaining controlled environments in various industrial and commercial applications.