Showing posts with label temperature. Show all posts
Showing posts with label temperature. Show all posts
Friday, June 6, 2014
Intelligent Temperature Monitoring and Control System using AVR Microcontroller
Controlling temperature has been a prime objective in various applications including refrigerators, air conditioners, air coolers, heaters, industrial temperature conditioning and so on. Temperature controllers vary in their complexities and algorithms. Some of these use simple control techniques like simple on-off control while others use complex Proportional Integral Derivative (PID) or fuzzy logic algorithms. In this project Shawon Shahryiar discusses about a simple control algorithm and utilize it intelligently unlike analogue controllers. Here are the features of this controller:
- Audio-visual setup for setting temperature limits.
- Fault detection and evasive action.
- Temperature monitoring and display.
- Audio-visual warning.
- System status.
- Settable time frame.
- Data retention with internal EEPROM memory.
Monday, September 30, 2013
Two Wire Temperature Sensor
Remote temperature measurements have to be linked by some sort of cable to the relevant test instrument. Normally, this is a three-core cable: one core for the signal and the other two for the supply lines. If the link is required to be a two-core cable, one of the supply lines and the signal line have to be combined. This is possible with, for instance, temperature sensors LM334 and LM335. However, these devices provide an output that is directly proportional to absolute temperature and this is not always a practical proposition. If an output signal that is directly proportional to the Celsius temperature scale is desired, the present circuit, which uses a Type LM45 sensor, offers a good solution.
The LM45 sensor is powered by an alternating voltage, while its output is a direct voltage. The supply to the sensor is provided by a sine-wave generator, based on A1 and A2 (see diagram). The alternating voltage is applied to the signal line in the two-core cable via coupling capacitor C6. The sensor contains a voltage-doubling rectifier formed by D1-D2-C1-C2. This network converts the applied alternating voltage into a direct voltage. Resistor R2 isolates the output from the load capacitance, while choke L1 couples the output signal of the sensor to the signal line in the cable.
Choke L1 and capacitor C2 protect the output against the alternating voltage present on the line. At the other end of the link, network R3-L2-C4 forms a low-pass section that prevents the alternating supply voltage from combining with the sensor output. Capacitor C5 prevents a direct current through R3, since this would attenuate the temperature-dependent voltage. The output load should have a high resistance, some 100 kΩ or even higher. The circuit draws a current of a few mA.
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The LM45 sensor is powered by an alternating voltage, while its output is a direct voltage. The supply to the sensor is provided by a sine-wave generator, based on A1 and A2 (see diagram). The alternating voltage is applied to the signal line in the two-core cable via coupling capacitor C6. The sensor contains a voltage-doubling rectifier formed by D1-D2-C1-C2. This network converts the applied alternating voltage into a direct voltage. Resistor R2 isolates the output from the load capacitance, while choke L1 couples the output signal of the sensor to the signal line in the cable.Choke L1 and capacitor C2 protect the output against the alternating voltage present on the line. At the other end of the link, network R3-L2-C4 forms a low-pass section that prevents the alternating supply voltage from combining with the sensor output. Capacitor C5 prevents a direct current through R3, since this would attenuate the temperature-dependent voltage. The output load should have a high resistance, some 100 kΩ or even higher. The circuit draws a current of a few mA.
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