Introduction to the LM335 Temperature Sensor
The LM335 is a precision, easily-calibrated, integrated circuit temperature sensor that operates as a 2-terminal zener diode. It provides a direct, linear output voltage proportional to the absolute temperature in Kelvin. The LM335 has a wide operating temperature range and low self-heating, making it suitable for many temperature sensing applications.
Key Features of the LM335
- Linear output: 10 mV/°K
- Wide operating temperature range: -40°C to +100°C
- Calibrated directly in Kelvin
- Low impedance output
- Easily calibrated
- Low cost
LM335 Configuration and Circuit Design
The LM335 is simple to use and requires minimal external components for operation. This section will cover the basic configuration and circuit design for the LM335 temperature sensor.
Basic LM335 Circuit
The most basic LM335 circuit consists of the sensor connected in series with a current-limiting resistor and a power supply. The output voltage is measured across the LM335.
+Vs
|
|
+-+
| |
| | R1
| |
+-+
|
+--- Vout
|
+-+-+
| |
| | LM335
| |
+-+-+
|
|
GND
The current-limiting resistor (R1) is chosen to provide a suitable current for the LM335, typically between 400 µA and 5 mA. The resistor value can be calculated using the following formula:
R1 = (Vs – Vout) / I
Where:
– Vs is the supply voltage
– Vout is the desired output voltage at a specific temperature
– I is the desired current through the LM335
Calibration and Accuracy
The LM335 is factory-calibrated to provide an output voltage of 2.98 V at 25°C (298.15 K). However, for better accuracy, it is recommended to calibrate the sensor for your specific application. Calibration can be done by measuring the output voltage at a known temperature and adjusting the resistor value accordingly.
The accuracy of the LM335 depends on several factors, including the calibration, the linearity of the sensor, and the self-heating effect. The typical accuracy of the LM335 is ±1°C over the rated temperature range.
LM335 Specifications
This section will cover the key specifications of the LM335 temperature sensor.
Electrical Characteristics
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| Calibration Voltage (25°C) | 2.95 | 2.98 | 3.01 | V |
| Calibration Error (25°C) | -2 | 0 | 2 | °C |
| Temperature Coefficient | – | -1.6 | – | mV/°C |
| Linearity | – | 0.5 | 2 | °C |
| Operating Temperature Range | -40 | – | 100 | °C |
| Operating Current | 400 | – | 5000 | µA |
| Self-Heating | – | 0.4 | 1 | °C/mW |
Physical Dimensions
The LM335 is available in various package types, including TO-92, TO-46, and SOT-23. The dimensions for the popular TO-92 package are:
- Height: 4.83 mm
- Width: 4.19 mm
- Depth: 4.19 mm
- Lead Pitch: 1.27 mm
LM335 Applications
The LM335 temperature sensor is used in a wide range of applications, including:
- Industrial process control
- Environmental monitoring
- HVAC systems
- Medical equipment
- Automotive temperature sensing
- Consumer appliances
Industrial Process Control
In industrial process control, the LM335 is used to monitor and control the temperature of various processes, such as chemical reactions, fermentation, and heat treatment. The sensor’s wide operating temperature range and low cost make it suitable for many industrial applications.
Environmental Monitoring
The LM335 is used in environmental monitoring systems to measure ambient temperature in buildings, greenhouses, and outdoor environments. The sensor’s linear output and ease of calibration make it a popular choice for these applications.
HVAC Systems
In heating, ventilation, and air conditioning (HVAC) systems, the LM335 is used to monitor and control the temperature of air and water. The sensor’s low self-heating and high accuracy ensure efficient and reliable operation of HVAC systems.
Medical Equipment
The LM335 is used in various medical equipment, such as incubators, blood analyzers, and patient monitors, to measure and control temperature. The sensor’s stability and reliability are critical in these applications.
Automotive Temperature Sensing
In automotive applications, the LM335 is used to monitor the temperature of various vehicle systems, such as the engine, transmission, and exhaust. The sensor’s wide operating temperature range and low cost make it suitable for automotive applications.
Consumer Appliances
The LM335 is used in consumer appliances, such as refrigerators, ovens, and air conditioners, to measure and control temperature. The sensor’s ease of use and low cost make it a popular choice for these applications.
Frequently Asked Questions (FAQ)
-
What is the LM335 temperature sensor?
The LM335 is a precision, easily-calibrated, integrated circuit temperature sensor that provides a linear output voltage proportional to the absolute temperature in Kelvin. -
What is the output voltage of the LM335 at 25°C?
The LM335 is factory-calibrated to provide an output voltage of 2.98 V at 25°C (298.15 K). -
How accurate is the LM335 temperature sensor?
The typical accuracy of the LM335 is ±1°C over the rated temperature range, depending on factors such as calibration, linearity, and self-heating. -
What is the operating temperature range of the LM335?
The LM335 has a wide operating temperature range of -40°C to +100°C. -
What are some common applications for the LM335 temperature sensor?
The LM335 is used in various applications, including industrial process control, environmental monitoring, HVAC systems, medical equipment, automotive temperature sensing, and consumer appliances.
Conclusion
The LM335 temperature sensor is a versatile, accurate, and cost-effective solution for a wide range of temperature sensing applications. Its linear output, wide operating temperature range, and ease of calibration make it a popular choice for industrial, medical, automotive, and consumer applications. By understanding the configuration, specifications, and applications of the LM335, designers can effectively integrate this sensor into their temperature sensing systems.
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